Uptake and transport in plants updated 2020

1 ADVANCED LEVEL TRANSPORT NOTES 2019 (modelled by king SOYEKWO ROGERS 07012119966
UPTAKE AND TRANSPORT IN PLANTS
Water and mineral salts are necessary for
photosynthesis reactions and other metabolic
processes; hence they must be absorbed in
sufficient quantities by using the root system
and transportingthemthroughthexylem to the
mesophyll cells of leaves where photosynthesis
takes place.
Water however can be lost from the mesophyll
cells into sub-stomatal air chambers and then
eventually lost into the atmosphere of water
vapourthroughtinypores called “stomata”by a
process known as transpiration.
TRANSPIRATION
This is the process of water loss inform of water
vapourto the atmospherefrom the plantmainly
through the stomata pores.
Types of transpiration
There are three types of transpiration which
include the following;
i. Stomatal transpiration
ii. Cuticular transpiration
iii. Lenticular transpiration
Stomatal transpiration
This is the loss of water vapour to the
atmosphere through the stomatal pores of the
leaves.
This contributes90% of the totalwater lossfrom
a leafy shoot. This is because leaves contain a
large number of stomata for gaseous exchange
where this water vapour can pass and also
there’s little resistance to the movement of
water vapour through the stomatal pores. In
addition, leaves also have a large surface area
over which water vapour can evaporate rapidly
to the atmosphere.
Cuticular transpiration
This is the loss of water vapour to the
atmosphere directly through the epidermis
coated with a cuticle layer.
It contributes 5% to the totalwater lossfrom the
leafy shoot. This is because the cuticle is hard,
waxy and less permeable to most diffusing
molecules including water vapour molecules.
Lenticular transpiration
This is the loss of water vapour through a mass
of loosely packed cells known as lenticels found
scattered on the stems.
It also contributes 5% of the total water loss to
theatmospherein a leafy shoot.It is because the
lenticels are usually few in number and not
directly exposed to environmental conditions.
Lenticular transpiration is the main source of
water loss from deciduous plants after shading
off theirleaves.Because there aremore stomata
on the leaves than elsewhere in the shoot
system, it is evidence that most of the water
vapour is lost from the leaves.
In order to establish that transpiration occurs
mostly in the leaves, an experiment using
absorptive paper, dipped Cobalt II Chloride
solution or Cobalt II thiocynate solution is
carried out. The paper is covered on the surface
of both sides of the leaves and then clamped
with glass slides. After some time, the blue
cobalt thiocynate paper changes to pink,
indicating the evaporation of water molecules
from the leaf by transpiration. The rate of
change from blue to pink is higher at the lower
epidermis than the upper epidermis. This is
because structurally there are more stomata on
the lower epidermis to prevent excessive loss of
water by transpiration due to direct solar
radiation.
Measuring the rate of transpiration

The rate of transpiration can be measured by
either determining the rate of transpiration at
which the plant loses mass due to water loss or
the rate atwhich the planttakesin water (water
uptake), using an instrument called a
potometer.
Determining the rate of transpiration using
a) the weighing method
The rate of mass loss by the plant can be
determined by using the potted plant placed on
an automatic weighing balance whereby the
change in mass is noted over a given period of
time. Using this method, it is assumed that the
mass loss is only due to water loss by
transpiration. However, the whole pot must be
enclosed in a polythene bag to prevent water
from evaporating from the soil. In addition, the
soil must be well watered before the beginning
of the experiment so that the plant has enough
water throughout the experiment. The rate of
transpirationis then expressed in terms of mass
lost per unit time
a) the potometer
The potometer is used to measure the rate of
water uptake by the shoot of the leafy plant.
However, since most of the water taken up is
lost by transpiration, it is assumed that water
uptake ≈ water loss. The leafy shoot is cut under
water to prevent the air bubbles from entering
and blocking the xylem vessels. The cut leafy
shootis immediately fixed in the sealed vesselof
connected to the capillary tube. The rate of
water uptake is then measured by introducing
an air bubble at the end of the graduated
capillary tube and the distance moved by the air
bubble per unit time is noted.
To drive the air bubble back to the original
position, water is introduced into the capillary
tube from the reservoir by opening the tap on
the reservoir.
The leafy area is also established by tracing the
outline of the leaves on a squared graph paper
and then counting the number of complete and
incomplete squares enclosed in the outline
The rate of transpiration is therefore expressed
in terms of the volume of water taken up by the
leafy shoot per unit time per unit leaf area. The
structure of a potometer is shown in the
diagram below.
Precautions taken when using a potometer
1. The leafy shoot used should have a
significant water loss by having very many
leaves
2. The stem of the leaf shoot must be cut
underwaterto preventair fromentering and
blocking the xylem vessels
3. The setup must have plenty of water
4. Ensure that only one bubble is present in
the capillary tube
5. A well graduatedscale must be used e.g.
a ruler, so that clear readings are taken

6. The air bubble should always be reset to
zero mark before the potometer is used
again under different conditions
7. The water reservoir should be filled with
water whensettingtheair bubbleatthe zero
mark
8. The cut leafy shoot must be in contact
with water in the sealed vessel
How to use a potometer
The leafy shootis cut underwater to preventair
bubbles from entering and blocking the xylem
vessels. The cut leafy shoot is immediately fixed
in the sealed vessel of water connected to a
capillary tube. Allow time (5 minutes) for the
apparatus to equilibrate. The rate of water
uptakeis measuredbyintroducingtheair bubble
at the end of the graduated capillary tube and
the distance moved by the air bubble per unit
time is noted. To drive theair bubbleback to the
original point, water is introduced into the
capillary tube from the reservoir by opening the
tap. The leafy areais thenestablishedby tracing
the outline of the leaves on squared papers and
then counting the number of complete and
incomplete squares in the outline of the leaves.
The rate of transpiration is therefore expressed
in terms of the volume of water taken up by the
leafy shoot per unit time per leafy area.
NOTE; since most of the water taken up by the
potometer is lost by transpiration, it is assumed
that water uptake = water loss.
Advantages of transpiration
1. It allows the uptake of water from the
roots to leaves in form of a transpiration
stream. This is due to a transpiration pull
created in the leaves. This ensures proper
distribution of water throughout the plant
to keep it alive.
2. It facilitates the uptake of the absorbed
mineral salts within the xylem vessels from
roots to leaves
3. It brings about the cooling of the plant
since as water evaporates to the
atmosphere, excessive heat is also lost as
heat of vaporization, which resultsinto the
cooling of the plant
4. It brings about mechanical support in
non- woody or herbaceous plants, due to
water uptake which provides turgidity to
the parenchyma cells of the stem and
leaves
5. It is important for cloud formation via
evapotranspiration hence resulting into
rainfall
Disadvantages of transpiration
i. It causes wilting of plants in case of
excessive transpiration
ii.It may eventually cause death of the
plant, when the plant loses water
excessively due to excessive transpiration
NOTE: wilting is the lossof water from the plant
cells. Evaporation occurs at rate greater than
that at which water is absorbed, resulting into
reductionin turgorpressureanddroppingof the
plant. It always takes place in hot and dry areas.
Wilting also results into the closure of the
stomata which cuts off gaseous exchange and
therefore may cause death if it persists.
FACTORS AFFECTING TRANSPIRATION
The potometer may be used to investigate the
effect of environmental factors on the rate of
transpiration i.e. it can be moved to a windy
place or a place which is dark. Transpiration is
affected by both environmental and non-
environmental factors.
ENVIRONMENTAL FACTORS

1. Humidity
The humidity of the atmosphere affects the
gradient of water vapour between the sub-
stomatal air chamber and the atmosphere
aroundtheleaf i.e. it affects the rateof diffusion
of water vapour. Low humidity (low water
vapour pressure) outside the leaf increases the
rate of transpiration because it makes the
diffusion gradient of water vapour from the
moist sub-stomatal air chamber to external
atmosphere steeper.
When humidity is high in the atmosphere, the
diffusion gradient or the water vapour pressure
gradient is greatly reduced between the sub-
stomatalairchamber andthe atmospherewhich
resultsintoreductioninthe rateof transpiration.
In areas where humidity is too high, plantsloose
liquid water from their leaves via
structures/glandsontheirleafmarginsknown as
hydathodes, a process known as guttation.
2. Temperature
Increase in temperature increases the rate of
water loss by the leaves via transpiration. A
decrease in temperature lowers the rate of
water loss by the plant leaves via transpiration.
This is because increase in temperature
increases the kinetic energy and movement of
water molecules hence the water molecules
evaporate rapidly to the sub-stomatalchambers
and eventually to the atmosphere via the
stomata. Increase in temperature also lowers
humidity outside the leaf which further
increases the rate of transpiration. In extremely
hot conditions, the stomata of some plants
close, an adaptation to prevent water loss by
transpiration.
3. Air movements
In still air (no wind), layers of highly saturated
vapour build up around the stomatal pores of
the leaf and reducesdiffusion gradient between
the stomatal air chamber and the external
atmosphere, thereby reducing the rate of
diffusion of water vapour from the leaf. The
layers of highly saturated water vapour which
build up around the stomatal pores of the leaf
are called diffusion shells. Windy conditions
result in increased transpiration rates because
the wind sweeps away the diffusion shells
around the leaf, thereby maintaining a steep
diffusion gradient which keeps the rate of
transpiration high.
4. Atmospheric pressure

Water vapour and the atmospheric pressure
decreases with increasing altitude. The lower
the atmosphericpressurethe greatertherate of
evaporation of water from the sub-stomatal air
chamber. This implies that plants growing on a
mountain have a higher rate of transpiration
than those growing in low land areas. However,
when the atmospheric pressure is high
e.g. in the lowland areas, the evaporation of
water vapourfromthesub-stomatalairchamber
to the atmosphere decreases, thereby
increasing the rate of transpiration.
5. Water availability
For water vapour to diffuse out of the sub-
stomatal air chamber to the atmosphere, the
mesophyll cells must be thoroughly wet.
Shortage of water in the soil or any mechanism
which hinders the uptake of water by the plant
leads towilting of the planthence the closureof
the stomata.
When water is supplied in large amounts, too
much water evaporates to the atmosphere and
therefore a high rate of transpiration. However,
when the water supply to the mesophyll cells is
low, less water evaporates from the sub-
stomatalto the atmosphere,hence a low rate of
evaporation.
6. Light intensity
It affects transpirationindirectly by affecting the
closure and opening of the stomata, which
usually opens in bright sunlight to allow
evaporation of water to the atmosphere.
Therefore sunlight increases the rate of
transpiration. At night and in darkness, the
stomata close and therefore there is no
evaporation of water from the sub-stomatal air
spaces to the atmosphere. This greatly lowers
the rate of transpiration in the plant.
NON-ENVIRONMENTAL FACTORS
1. Leaf area
The larger the leaf surface area on the plant, the
higher the rate of water loss by transpiration.In
addition, broad leaves provide a large surface
area over which water vapour diffuses to the
atmosphere as compared to the narrow leaves.
2. Cuticle
The thinner the cuticle, the higher the rate of
water loss by transpiration and the thicker the
cuticle, the lower the rate of water lossfrom the
plantto the atmosphereby transpiration.This is
because this offers a significant resistance
towards the diffusion of water vapour from the
plant to the atmosphere.
3. Number of stomata
The larger the number of stomata on the plant,
thehigherrate of waterlossby transpirationand
the lower the numberof stomata, the lower the
rate of transpiration.
However, a very large number of stomata so
close to each other may instead reduce the rate
of transpiration especially in still air due to the
accumulationof water vapouraroundthewhole
stomata pore.
Guttation
Guttation is the loss of liquid water from plant
leaves through hydathodes due to excessive
humidity in the atmosphere. Hydathodes are
pores in the epidermis of leaves that exudes
drops of water. They are abundant in leaves of
submerged plants like water hyacinth, water
lettuce and herbaceous plants.
WATER UPTAKE BY THE ROOTS
M Internal structure of the root
The root consists of various tissues which occur
in concentric layers. The cells at the surface of
the young root forming the piliferous layer are

so called because it is by the root hairs. As the
roots get older, they increase in girth (thickness
or diameter), the piliferous layer (breaks)
raptures and peels off leaving the outer most
layer of cells known as epiblem, to become the
functional o uter layer.
Next totheepiblem is thethicker layerof loosely
packed parenchyma cells, known as cortex.
Adjacent to the cortex is a layer of cells known
as endodermis.
The endodermal cells have their radial and
horizontal wallscoated with a corky band called
casparian strip. This strip is made up of a
substance cal led suberin. The Casparian strip
is impermeable to water and solutes due to the
suberin that it contains and therefore prevents
water and solutesto pass throughthe cell walls
to the endodermis. The endodermis also
contains starch grains.
Next to the endodermis is another layer of cells
known as pericycle from which lateral roots
develop. The pericycle, that is made up of
parenchyma cells which encloses the vascular
bundles(xylem and phloem) in the centre of the
root.
DIAGRAM OF THE TRANSVERSE SECTION OF
THE ROOT
Longitudinal section through a root
Mechanism of water uptake by the roots
For water to be transported up to the leaves
throughthe stem, it must be absorbed from the
soil by the tiny root hairs. Root hairs penetrate
the soil particles and absorb water from the
airspaces
Root hairs are numerous in number, lack cuticle
and hence increase the surface area for
absorption of water. Water absorption into the
root hairs occurs by osmosis. This is due to the
water potential of the cell sap of the root hairs
being lower thanthat of the soil solution (water
content). The lower water potential of the root
cells is due to presence of sugars and other
metabolites in the cell sap and cytoplasm of the
root cells.
When the root hair absorbs water, its water
potential increases and becomes higher than
that of the adjacent cells of the root. This
facilitates the flow of water from the root hairs
to the endodermalcells across a water potential
gradient.
Water flows by osmosis form the root hairs to
the endodermal cells using three pathways,
namely;
a) Apoplast (cell wall) pathway
b) Symplast (cytoplasm) pathway
c) Vacuolar pathway
Apoplast pathway
a)
b)
c)

This is the pathway in which water moves
throughthe spaces between the cellulose fibres
in the cell wall of one cell to the cell wall of the
adjacent cells.
However, this movement does not occur within
the endodermal cells because they possess the
impermeable casparian strip which prevents
water and solutesflow throughthe cell walls of
the endodermalcells.This means thatwater and
solutes flow through the cell walls of the
endodermal cells via the Symplast and the
vacuolar pathways only.
The significance of this Casparian strip is to bring
about active pumping of salts (ions) by the
endodermalcells,from thecortex intothe xylem
vessels of the roots, which creates a high solute
concentration in the xylem, thereby greatly
loweringthe waterpotentialin the xylem thanin
the endodermis. This makes the water potential
of the xylem vessels more negative (very low)
and results into rapid osmotic flow of water
from the endodermalcells to the xylem vessels,
due to the steep water potential gradient
between the endodermal cells and the xylem
vessels.
The Casparian strip facilitates the pushing of
water upwards through the xylem vessels by
root pressure up to the leaves due to its active
pumping of the salts. In addition, this active
pumping of the salts into the xylem vessels
preventsleakage of salts(ions) out of the xylem
vesselssoas to maintaina low water potentialin
this vessel.
Qn Explain theroleofCasparian stripin transport
of materials in plants (10 marks)
A diagram showing the structure of the Casparian
strip.
A graphshowingwater uptake at different partsofa
bean root
Explain the changes in rate of water uptake in the
graph above.
Symplast pathway
This is the movement of water through the
cytoplasm of one cell to the cytoplasm of the
adjacent cell via plasmodesmata. Cell contents are
connected to one another by the plasmodesmata
through which cytoplasmic strands run from cell to
cell.
Water leaving the pericycle cells to enter the xylem
causes the water potential of these cells to become
more negative (more dilute). This facilitates the flow
of water by osmosis from the adjacent cells into
these cells. In this way the water potential gradient
from the root hairs to the xylem is established and
maintained across the root. This pathway offers a

significant resistance to the flow of water unlike the
apoplast pathway.
Vacuolar pathway
This is the movement of water from the sap vacuole
of one cell to the sap vacuole of the adjacent cell
following a water potential gradient.
This is achieved by maintaining a steep water
potential gradient. However, this also offers a
reasonable level of resistance towards water flow in
comparison to the Symplast pathway.
Note; the apoplast is the most appropriate pathway
in plants because it provides less resistance to water
flow in the plant.
Diagram showing the three pathways of water in
the root
To ensure maximum absorption of water, the
root hairs have the following adaptations
a) They are numerous in number so as to
provide a large surface area for the
maximum absorption of water by osmosis.
b) They are slender and flexible for easy
penetration between the soil particles so as
to absorb water.
c) The lack a cuticle and this enhances the
passive osmotic absorptionof water without
any resistance
d) They have a thin and permeable membrane
which allows the absorption of water by
osmosis.
e) They have a water potential lower than that
of the soil solution which facilitates a net
osmotic flow of water from the soil
Movement of water into the vascular tissue of
the roots.
Water passes through the parenchyma cells of
the roots into the vascular tissue of the roots
due to the following forces:
a) Transpirational pull.
This is exerted due to the lower water
potential that develops in the cells of the
leaves as a result of transpiration. This force
pulls water or exerts a sunction
force/pressure on the water on the narrow
xylem vessels and tracheids which pulls
water in a single continuous stream.
b) Root pressure:
Root pressureis the force developed by cells
of the roots which forces water from the
endodermal cells into the xylem vessels of
the root and constantly forces water
upwards through the stem to leaves. This
process is active and involves utilization of
many ATP molecule. Root pressureoccurs as
a result of endodermal cells actively
secreting salts into the xylem sap from their
cytoplasm, which greatly lowers the water
potential in the xylem.
The endodermal cells have their cell walls
coated with suberin in form of casparian
strips, hence impermeable towards water
movement through the cell walls.
In some plants, root pressure maybe large
enough to force liquid water through pores
called hydathodes of the leaves in a process
called guttation
Evidence to support the mechanism of water
uptake from the endodermis into the xylem
vessel as an active process
a) There are numerous starch grains in
endodermal cells which could act as an
energy source for active transport.
b) Lowering the temperature reduces the rate
of water exudation (given out) from the cut

stem as it prevents root pressure, an active
process.
c) Treating the roots with metabolic poisons
e.g. potassium cyanide also prevents water
from being exuded from the cut stems. This
is because the poisons kill the cells thereby
preventing aerobic respiration, a source of
ATP molecules.
d) Depriving roots of oxygen prevents water
from being exuded from the cut stems. This
showsthatwaterwasbeing pushedupwards
in the cut stem by root pressure, an active
pressure.
The following is the evidence to show that
water moves by pressure in a plant.
When the stem of a plantis cut water continues
to exude from the xylem vessels of the plant
stem. The continuous exudation of water from
the xylem vessels of the cut stem is due to root
pressure because the leafy shoot is cut off,
meaning that water not only moves upwards by
transpiration pull, but also due to pressure and
other forces.
Rootpressure canbe measured usinga mercury
manometer whose diagram is shown below
Though it is true that water moves from the
roots through the stem to the leaves by
transpiration pull, root pressure partly
contributes towards the movement of water
from the parenchyma cells to the xylem of the
root,to the stem andeventuallyupto the leaves
THE UPTAKE OF WATER FROM THE ROOTS TO
THE LEAVES
The movement of water from the roots to the
leaves is by combination of different forces
which include the following;
A. Root pressure
B. Transpiration pull (cohesion force)
C. Capillarity
1. Root pressure
This enables movement of water from the
parenchymacells of themain rootintothe xylem
tissue due to the active pumping of cells from
endodermal cells into the xylem tissue.
Root pressure also ensures upward movement
of water throughthexylemtissuestothe leaves.
2. Transpiration pull (cohesive force/cohesion-
tension theory of water uptake)
This explains the continuous flow of water
upwardsthroughthexylemof the planti.e. from
the root xylem to the stem xylem and finally to
the leaf xylem.
Water is lost from the plant leaves by
transpirationwhich creates a tension within the
leaf xylem vessels that pulls water in the xylem
tubes upwards in a single unbroken column or
string held together by the cohesive forces of
attraction between water molecules.
According to the cohesion-tension theory,
evaporationof waterfrom the mesophyllcellsof
the leaf to the sub-stomatal air chamber and
eventuallytothe atmospherevia the stomataby
transpiration, is responsible for the rising of
water from the roots to the leaves. This is

because the evaporated water molecules get
replaced by neighbouring water molecules
which in turn attract their other neighbouring
water molecules and this attraction continues
until the root is reached.
Evaporation of water resultsin a reduced water
potential in the cells next to the leaf xylem.
Water therefore enters these mesophyll cells by
osmosis from the xylem sap which has the
higher water potential. Once in the mesophyll
cells water moves using the three pathways
namely; apoplast, Symplast and vacuolar
pathways from one cell to another by osmosis
across a water gradient.
When water leaves the leaf xylem to the
mesophyll cells by osmosis, a tension is
developed within the xylem tubes of water
which is transmitted to the roots by cohesive
forces of water molecules.The tension develops
in the xylem vessels and builds up to a force
capable of pulling the whole column of water
molecules upwards by means of mass flow and
water enters the base of these columns from
neighboring root cells. Because such a force is
due to water loss by osmosis by transpiration,it
is referred to as transpiration pull.
3. Capillarity
Since the water rises upwards through narrow
leaves, it is also facilitated by capillarity through
the stem.
This is because thexylem vesselsare too narrow
and the flow of water is maintained without
breaking by both the cohesive and adhesive
forces.
The role of transpiration in the movement of
water through the whole plant
 Water evaporates from the cellulose cell
walls of the spongy and palisade mesophyll
into the sub- stomatal air spaces of the
leaves.The water vapor is lost to the external
environment through the open stomata.
 Turgor pressure of the mesophyll cells falls
and water enters the mesophyll cells from
xylem vessels and tracheids of the leaves by
osmosis.
 This causes water to be drawn rapidly from
the xylem tissue of the stem into the xylem
tissue of the leaves.
 A tension develops in the xylem tracheids
and tissues of the stems.
 The cohesion and adhesion forces in the
narrow xylemvessels and tracheids increase.
 Increase in cohesion forces prevents long
water column from breaking in between
while adhesion forces prevent the mass of
water from falling back and instead a mass
flow of water occurs in a long continuous
column. This is called cohension-tension
theory.
 Watercontinues to flow in the xylemvessels
and tracheidsof the roots andstems to those
of the leaves due to transpiration until turgor
pressure inthe roots falls below atmospheric
pressure. The water begins to move by
osmosis from the soil into the root xylem
tissue across parenchyma cells via three
pathways: symplast, vacuolar and apoplast
until it reaches the endodermis where the
apoplast pathway is prevented by the
casparian strips.
 All the water is now diverted to the symplast
and vacuolar pathway. Root pressure
develops which forces the water into the
root xylem and tracheids.
 The endodermis also secretes salts into the
root xylem vessels, which lowers the water
potentials of the xylem of the root. Water is
then drawn into the root xylem by osmosis
from the surrounding cells.
An illustration to show how transpiration pull is
created.

Qn. a). Describe the role of transpiration in the
movement of water up a plant (10 marks)
Explain the role of transpiration in the movement
of water up a tall plant (10 marks)
The diagram below shows the upward
movement of water from the soil up to the
leaves.
NOTE
1. The continuous mass flow of water through
the xylem vesselsfrom the rootsto the leaves in
a stream without breaking, due to the
transpiration pull is called the transpiration
string
2. Adhesion is the force of attraction between
molecules of different substances while
cohesion is the force of attraction between
molecules of the same substance.
Question: An experiment to determine the
relationshipbetween rateofabsorption ofwater
and rate of transpiration in sunflower at
different times of the day was carried out. The
graph below shows the results of the findings:
Summary of movement of water in a plant.
TYPICAL EXAMINATION QUESTION
1. In an investigation on transpiration,
twelve twigs of approximately the same
age, leaf surface area and from the same
plant species were used in an
experiment. The twigs were divided into
three groups of four and each group
treated simultaneously as follows:
Group 1: Twigs completely covered with
transparent polythene bags
Group 2: Twigs fanned with electric fans

Group 3: Twigs placed in still air in the open.
The table below gives a summary of the
results of the mean values in cm3 of four
readingstakenin each grouprepresentedon
the table as A, B and C.
Time of day
(hours)
Mean
readings (cm3)
A B C
08.00 2.0 2.0 2.0
09.00 3.0 2.4 2.5
10.00 4.2 2.6 3.4
11.00 5.4 2.7 4.4
12.00 7.1 2.8 5.5
13.00 9.6 2.9 7.0
14.00 13.1 2.9 9.5
15.00 16.6 2.9 11.5
16.00 18.1 2.9 13.0
17.00 19.0 3.0 13.6
18.00 19.5 3.1 13.9
a) Calculate the mean cumulative volume
of waterlost ineach hourby the twigsof
group A and B and record them in an
appropriate table. (4marks)
Table of mean cumulative volume of water lost
in each hour by the twigs of group A and B
Time of the day (hours)
Cumulative
volume of water
lost/hour/cm3
A B
08:00 2.0 2.0
09:00 5.0 4.4
10:00 9.2 7.0
11:00 14.6 9.7
12:00 21.7 12.5
13:00 31.3 15.4
14:00 44.4 18.3
15:00 61.0 21.2
16:00 79.1 24.1
17:00 98.1 27.1
18:00 117.6 30.2
b) Using suitable scales and the same axes,
draw curves to show the relationship
between:
i) The mean cumulative volume of
water lost by the twigs of group
A and B with time.
ii) The mean volume of water lost
per hour by the twigs of group C
with time. (9 marks)
c) From the curves drawn, identify the
experimental condition to which each
group of twigs A, B and C were placed.
(3 marks)
A-Twigs fanned with electric fires
B-Twigs completely covered with transparent
polythene bags
C- Twigs placed in still air in the open.
d) With respect to twigs of A and B, give
reasons for the observed differences in
the two curves drawn.
(7marks)
Themeancumulativevolumeofwater lost perhour by
twigsofgroupAincreases rapidly; withincrease in day
time while the mean cumulative volume of water lost
per hour of groupB increases gradually; with increase
in day time.
This is because the electric fan creates air currents or
movements; which rapidly sweep; away the water
vapour diffusing from the intercellular spaces; via the
stomata; which increases the water vapour gradient;

by removing the vapour; and creating space for more
vSapour to occupy. This increased water
vapour/diffusiongradient resultsin therapid diffusion
ofwater vapour; fromtheintercellular space totheair
surrounding the twigs.
IntwigsofgroupB,theincrease isgradual becausethe
twigs are completely covered with a polythene bag
and the diffusing water; accumulates and saturates
the immediate air surrounding of the twigs hence
reducing; the vapour/diffusion gradient which results
in a verygradual increase; in waterdiffusionin form of
vapour from the twigs’ intercellular space to the
immediate air surrounding.
@ 0.5 marks, max7 marks
e) Explain why the rate of water loss
throughout the day varies as shown in
curve C above. (9 marks)
From08:00hoursto13:00hours;therateofwaterloss
increases gradually; due to slow increase in
temperature; light intensity and a very slow decrease
in humidity; from morning hours to around midday.
Under such a slowchange in theaboveconditions,the
rate of evaporation; and water vapour diffusion
increases slowly;stomatadiameterwidensslowly;and
the water vapour diffusion gradient between the
intercellular spaces and the surrounding air increases
slowly; hence the gradual increase in the rate of
transpiration.
From 13:00 hours to 15:00 hours; in the immediate
afternoon, the rate of water loss increases; at a
relatively fast rate since humidity is already low; and
with the relatively high temperatures; humidity
decreases;at a relatively fast ratehenceincreasing the
rate of water vapour diffusion to the surrounding
which is further increased by the increased diameter;
of the stomata.
Furtherincrease in day time from 15:00hours to18:00
hours; results in a slow/gradual increase; in the mean
volume of water lost by the twigs. Such a day time
rangeis associatedwithreductionin light intensity;air
temperature and consequently increase in humidity;
which coupled with a gradual reduction in stomata
diameter;slows therateof transpiration;andthehigh
humidity creates a relatively low water vapour
diffusion gradient which reduces the rate of
transpiration. @ 0.5 marks, max 9 marks
f) Why were twigs of the same age, leaf
surface and same plant species used in
the investigation? (3 marks)
Twigs of the same age, leafsurface areaand plant
species were used to obtain consistent accurate
results; becausedifferent ages of leavestranspire
at different rates; that is very young and very old
leaves transpire at a lower rate; compared to the
middle aged leaves and the observed differences
would not be attributed by environmental
conditions associated with the day’s time range
only.
If different surface areas of leaveswere used, the
leaves would transpire at different rates since
leaves with larger surface area avail a wide
platform; over which heat is absorbed and over
which transpiration can occur;
Sameplant speciestranspireat the same rate but
different plantspeciestranspireat different rates

due to differences in stomatal density; stomatal
distribution and leaf shoot ratio; Aquatic species
with high transpiration ratesandxerophytes with
low transpiration rates.
g) It is observed that a tree canopy withan
area of 20m2 loses greater amount of
water in a given length of time than a
water body with the same surface area.
Suggest an explanation for this
observation (5 marks)
Tree canopy loses greateramounts of water than
a water body of the same surface area due to a
number of factors; which include which increase
speed of water movement from the soil to the
leaves and out of the plant; which include
 The root pressure pushes water up the
plant to the leaves;
 Transpiration pull; pulls water molecules
to higher parts of the tree in the
transpiration stream;
 The vessels through which eater is raised
that is the xylem vessels; are very narrow
hence increasing the capillarityforce;with
which water is transported to structures
where it is lost from.
 Strong cohesive forces of attraction; hold
water molecules together; so that they
move up the plant in a continuous
unbroken stream to structures where it is
lost from.
 Adhesive forces; of attraction stick the
water molecules to the xylem vessels
walls;enablingwatertoeasilymoveupthe
xylem vessel in an unbroken column; to
structures where it is lost from,
TOTAL = 40 MARKS
UPTAKE AND TRANSLOCATION OF MINERAL
IONS
Translocation is the movement of mineral salts
and chemical compounds within a plant.
There are two main processes of translocation
which include;
a. The uptake of soluble minerals from
the soil and their passage upwards from
the roots to the various organs via the
xylem tubes.
b. The transfer of organic compounds
synthesized by the leaves both upwards
and downwardsto variousorgansvia the
phloem tubes
Mechanism of mineral ion uptake
Mineralssuch asnitrates, phosphates,sulphates
etc. may be absorbedeitheractively orpassively.
1. Active absorption of minerals
Most minerals are absorbed from the soil
solution having the less mineral concentration
into the root hairs with the higher mineral
concentration, selectively by using active
transport which uses a lot of energy.
The rateof active absorptionof mineralsinto the
root hairs depends on the rate of root
respiration. Factors such as oxygen supply and
temperature will affect the rate of ion uptake.
The addition of respiratory poison hasshownto
inhibit uptake of mineral ions.
2. Passive absorption
If theconcentrationof amineral in a soilsolution
is greater than its concentration in the root hair
cell, the mineral may enter the root hair cell by
diffusion.
Mass flow or diffusion occurs once the minerals
are absorbedby theroothairs sothatthey move
along cell walls (apoplast pathway). In mass
flow, the mineral ions are carried along in
solution by water being pulled upwards in the

plant in the transpiration stream, due to the
transpirationpulli.e. the mineral ions dissolve in
water andmove within thewater columnsbeing
pulled upwards.
The mineral ions can also move from one cell of
the root to another against the concentration
gradient by using energy inform of ATP.
The mineral ions can also move through the
Symplast pathway i.e. from one cell cytoplasm
to another.
When the minerals reach the endodermis of the
root, the Casparian strip prevents their further
movement along the cell walls (apoplast
pathway). Instead the mineral ions enter the
cytoplasm of the cell (Symplastpathway) where
they are mainly pumped by active transportinto
the xylem tissues and also by diffusion to the
xylem.
Once in the xylem, the minerals are carried up
the plant by means of mass flow of the
transpiration stream. From the xylem tissues,
mineralsreach theplaces wherethey are utilized
called sinks by diffusion and active transporti.e.
the minerals move laterally (sideways) through
pits in the xylem tissue to the sinks by diffusion
and active transport.
Evidence to show that most mineral ions are
absorbed actively by the root hairs
a) Increase in temperature around the plant
increases therate of mineral ion uptakefrom
the soil as it increases respiration that can
provide energy for active transport
b) Treating the root with respiratory inhibitors
such as potassium cyanide prevents active
mineral ion uptake leaving only absorption
by diffusion. This is because the rate of
mineral ion uptake greatly reduces when
potassium cyanide is applied to the plant.
c) Depriving the root hairs of oxygen prevents
active uptake of mineralsby the rootsand as
Evidence for supportingthe role of the xylem in
transporting minerals
1. The presence of mineral ions in the xylem
sap i.e. many mineral ions have been
found to be present in the xylem sap.
2. There’s a similarity between the rate of
mineral ion transport and the rate of
transpiration i.e. if there’s no
transpiration,thenthere’s no mineral ion
transport and if transpiration increases,
the rate of mineral ion transport also
increases.
3. There’s evidence that other solutes e.g.
the dye, eosin, when applied to the plant
roots, it is carried in the xylem vessels
4. By using radioactive tracers e.g.
phosphorous-32. When a plant is grown
into a culture solution containing
radioactive phosphorous-32,
phosphorous -32 is found to have
reached all the xylem vesselsbut not the
phloem tubes.
5. The interpretation of these elements is
that where lateral transfer of minerals
cantake placea resultveryfew ions enter
the plant by diffusion.

NOTE; Some plantsabsorbmineralsaltsby using
mutualisticassociationsbetween their rootsand
other organisms e.g. the association between
the fungus and the higher plant roots called
mycorrrhiza.
TYPICAL EXAM QUESTIONS
The relationship between potassium ion
concentration in the roots and sugar
consumption at different oxygen concentration
was investigated. The figure 1 below shows the
concentration of potassium ions (Mgcm-3) and
the rate of sugarconsumption (Mghr-1)byroots
of fleshly uprooted plant when inserted in a
bathing fluid at different oxygen concentration.
(a) Compare the effects of oxygen
concentration on potassium ion
concentration in the roots and rate of
sugar consumption. (07 marks)
Similarities.
Both potassium ion concentrations and sugar
consumption in roots,
- Increased up to the maximum;
- Increased rapidly upto 10% oxygen
concentration and then gradually upto
50% oxygen concentration;
- Reached their maximums levels;
- Remained constant from 55 upto 60%
oxygen consumption;
- Where at their lowest valuesat 0% oxygen
consumption;
- Have the same value at 5% oxygen
consumption @ 1 mark,
max = 03 marks.
Differences,
- Rate of sugar consumption is higher while
potassium ion concentration is lower from
0 upto 5% oxygen consumption;
- Potassium ion concentration is higher
while rate of sugar consumption is lower
from 5 upto 60% oxygen consumption;
- Potassium ion concentration increased
more rapidly while rate of sugar
consumption increased rapidly from 0
upto 10% oxygen consumption;
- Potassium ion concentration increased
more gradually while rate of sugar
consumption remained constant from 50
upto 55% oxygen consumption;
- Maximum potassium ion concentration
reached is higher than maximum reached
by rate of sugar consumption;
- Rate of potassium ion concentration
reached peak at relatively lower
percentageof oxygen consumption of 50%
while potassium ion concentration
reached peak at relatively higher
percentageof oxygen consumption of 55%
; @
1 mark, max = 04 marks.
(b) Explain the,

(i) Presence of potassium ion
concentration in the roots without
oxygen. (05 marks)
(ii) Relationship between potassium ion
concentration and oxygen
consumption.
(12 marks)
(iii) Effect of increasing percentage of
oxygen consumed on rate of sugar
consumption.
(08 marks)
b (i)
Some little potassium ions were passively
absorbedfrom the solution by diffusion and mass
flow; due to potassium ions concentration
gradient that existed; anaerobic respiration
occurred; producing small amounts of energy in
form of ATP; which was used for small active
uptake of small amounts of potassium ions; root
hair cells contained some small amounts of
potassium ions before being uprooted
@ 1 mark, max = 05 marks
b (ii)
Initially/at0%oxygen consumption; concentration
of potassium ions is low; because uptake of small
amounts of potassium ions into the root hair cells
is only passively by diffusion/Anaerobic
respiration produced small amount of energy
inform of ATP which wasused for activetransport
of small amounts of potassium ions ;
As oxygen consumption increases from 0 upto
10%, potassium ion concentration increased
rapidly ; because of rapid aerobic respiration ;
producing largeamounts of energy inform of ATP
molecules; resulting into activetransportof large
amounts of potassium into root hair cells ; some
potassium ions diffused into the root hair cells ;
As oxygen consumption increases from 10 upto
55%, potassium ion concentration increased
gradually ; respiratory substrate sugars is getting
depleted ; resulting into slow aerobic respiration
; small amount of energy inform of ATP molecules
is produced ;
As oxygen consumption increased from 55 upto
60 percent, potassium ion concentration
remained constant ; no ATP produced from
aerobic respiration and no active uptake of
potassium ions into the root cells ; @ 1 mark ,
max = 12 marks
b (iii)
Increase of percentage of oxygen consumption
from 0 upto 10% causes rate of sugar consumption
to increase rapidly ; This is because oxygen is a
metabolite for aerobic respiration ; increase in
percentage consumption of oxygen increases
oxidative breakdown of sugars/metabolism of
sugars to generate energy inform of ATP ;
Increase of percentage of oxygen consumption
from 10 upto 50% caused rate of sugar
consumption to increase gradually upto the
maximum ; sugar as a respiratory substrate is
getting depleted ;enzyme responsible for aerobic
respiration is getting denatured ; by low pH (high
hydrogen ions levels in solution) and oxygen
poisoning ; oxidative breakdown of sugars are
lowered ;

Increasing percentage of oxygen consumption
from 50 upto 60% caused rate of sugar
consumption to remain constant ; no further
breakdown of sugars to generate energy ; since
enzymes are completely denatured ; sugars may
be completely depleted.
@ 1 mark , max = 08 marks
(c) Predict change in concentration of
potassium ions in the roots and rate of
sugar consumption if the experiment
was to continuefor some time up to 90%
oxygen consumption. Suggest reasons
for your answer.
(05 marks)
Potassium ion concentration in the root cells will
decrease until the concentration remains
constant at verylow values; becausethere are no
more energy for activeuptakeof potassium ions ;
yet potassium ions in the root hair cells are
transported away through the xylem vessels and
tracheids to other regions of the plant where the
ions will be utilized for protein synthesis/building
up new plant tissues ; concentration of the
potassium ions remainconstant when the ions are
depletedinthebathingsolution or no more active
uptake of the ions into the root cells ;
Rate of sugar consumption will remain constant ;
sugar molecules in the solution is
depleted/enzymes for aerobic respiration are
denatured and no further metabolism of sugar
taking place ; @ 1 mark , max = 05 marks
(d) State other three factors other than
oxygen concentration that could affect
the rate of potassium ion uptake by
roots. (03 marks)
- Low or high temperaturesbelowor above
the optimum ;
- Concentration of potassium ions in the
solution ;
- Surface area of the root hairs ;
- Presence of inhibitors/metabolic poisons ;
- pH levels @ 1 mark ,
max = 03 marks
TRASLOCATION OF ORGANIC MOLECULES
(food molecules in the phloem)
The organic materials produced as a result of
photosynthesis;needto be transportedtoother
regions of the plant where they are used for
growthorstorage.Thismovementtakesplace in
the phloem tissue particularlyin the sieve tubes.
Evidence to support that organic molecules of
photosynthesis are transported in the phloem
a) When the phloem is cut, the sap which
exudes out of it is rich in organic food
materialsespecially sucroseandamino acids.
b) The sugar content of the phloem varies in
relation to environmental conditions. When
the conditions favor photosynthesis, the
concentration of the sugar in the phloem
increases and when they not favor
photosynthesis and concentration of the
sugar in the phloem reduces.
c) Removal of a complete ring of phloem
around the phloem causes an accumulation
of sugar around the ring, which results into
the swelling of the stem above the ring. This
indicates that the downward movement of
the sugars has been interrupted and results
into the part below the ring failing to grow
and may dry out. This is called the ringing
experiment.
TOTAL = 40 MARKS

d) The use of radioactive tracers. If radioactive
carbon dioxide-14 is given to plants as a
photosynthetic substrate, the sugars later
found in the phloem contain carbon-14.
When the phloem and the xylem are
separated by waxed paper, the carbon-14 is
found to be almost entirely in the phloem.
e) Aphidshaveneedle like probosciswith which
they penetrate the phloem so as to suck the
sugars. If a feeding aphid is anaesthetized
using carbon dioxide or any other chemical
e.g. chloroform and then its mouthparts cut
from the main body, some tiny tubes called
the proboscis remain fixed within the
phloem sieve tubes from which samples of
the phloem content exudes.
f) When the contents of the phloem are
analyzed, they are confirmed to be
containing carbohydrates, amino acids,
vitamins e.t.c. which further confirms that
the phloem transports manufactured foods.
g) When smallsectionsof the pierced stemsare
cut following the proboscis penetration, the
tips of the proboscis are found within the
phloem sieve tubes.
Ringing experiments
MECHANISM OF TRANSLOCATION IN THE
PHLOEM
It was found out that organic materials do not
move through the phloem sieve tubes by
diffusion because the rate of flow of these
materialsis too fastfor diffusion tobe the cause.
The mechanism of translocation of food in the
phloem is explained by the following theories or
hypothesis.
1.The massflow orpressureflowhypothesis (i.e.
Munch’s hypothesis)
2. Electro-osmosis
3. Cytoplasmic streaming
Mass flow or pressure flow
hypothesis/munch`s hypothesis
Mass flow is the movement of large quantities of
water and solutes in the same directions.
According to this theory, photosynthesis forms
solublecarbohydrates like sucrose in the leaves.
The photosynthesizing cellsin the leaf therefore
have their water potential lowered due to the
accumulation of this sucrose.
Sucrose is actively pumped into the phloem
sieve tubes of the leaf. As a result, water which
has been transported up to the stem xylem
enters these sieve tubes by osmosis due to the
accumulationof sucrose.This causes anincrease
in the pressure potential of the leaf cells
includingthe leaf sieve tubeelementsmore than
thatin thecells in the sink i.e. the mesophyllcells
where the sugarsaremanufacturedare referred
to as the source while the other parts of the
plantsuchas the roots where food is utilized are
referred to as the sink.
The food solution in the sieve tubes thenmoves
from a region of higher-pressurepotentialin the
leaves to that of lower pressurepotential in the
sink such as roots following a hydrostatic

pressuregradient.Attheotherpartsof theplant
which form the sink e.g. the roots, sucrose is
either being utilized as a respiratorysubstrateor
it is being converted into insoluble starch for
storage, after being actively removed from the
sieve tubes and channeled into the tissues
where they are required. The soluble content of
thesink cellstherefore is lowandthis givesthem
a higherwaterpotentialand consequentlylower
pressure potential exists between the source
(leaves) and the sink such as roots and other
tissues
The sink andthesource arelinked by the phloem
sieve tubes and as a result the solution flows
from theleaves toothertissues(sinks)alongthe
sieve tube elements.
A diagram showing movement of the products
of photosynthesis by mass flow
Evidence supporting the mass flow theory
1. When the phloem is cut, the sap exudes
out of it by mass flow
2. There’srapid andconfirmed exudationof
the phloem’s sap from the cut mouth parts
of the aphids which shows that the content
of the sieve tubes moves out at high
pressure.
3. Most researchers have observed mass
flow in microscopic sections of the sieve
tube elements.
4. There’s some evidence of concentration
gradient of sucrose and other materials
with high concentration in the leaves and
lower concentration in the roots.
5. Any process that can reduce the rate of
photosynthesis indirectly reduces the rate
of translocation of food.
6. Certain viruses are removed from the
phloem in the phloem translocationstream
indicating that mass flow rather than

diffusion, since the virus is incapable of
locomotion.
Criticism of mass flow
1. By this method all organic solutes would be
expected to move in the same direction and at
the same speed. It was however observed that
the organic solutes move in different directions
and at different speeds.
2. The phloem has a relatively high rate of
oxygen consumptionwhich this theory does not
explain.
3. When a metabolic poison such as potassium
cyanide enters the phloem, the rate of
translocation is greatly reduced, implying that
translocation is not a passive process, but an
active one.
4. The mass flow hypothesis does not mention
any translocation of solutes with influence of
transfer cells and Indole Acetic Acid (IAA)
hormone that loads the sugars or solutes into
the sieve tubes and also unload it into the cells
of the sink.
5. The sieve plates offer a resistance which is
greater than what could be overcome by the
pressure potential of the phloem sap. This
implies thatthe pressurewould sweep away the
sieve plates during this transport.
6. Higher pressure potential is required to
squeeze the sap through the partially blocked
poresin the sieve platesthanthepressurewhich
has been found in the sieve tubes
NOTE: the mass flow theory is considered to be
the most probable theory in conjunction with
electro-osmosis.
Electro-Osmosis
This is the passage of water across a charged
membrane.
This membrane is charged because positively
charged ions e.g. K+ , actively pumped by the
companion cells across the sieve plate into the
sieve tubeelement usingenergy from ATPof the
companion cells.
Potassium ions accumulate on the upper side of
the sieve plate thereby making it positively
charged.Negatively chargedions accumulateon
the lower sides of the sieve plate thereby
making it negatively charged. The positive
potential above the sieve plate is further
increased by hydrogen ions, actively pumped
from the wall to the upper sieve tube element
into its cytoplasm.
Organic solutes such as sucrose are transported
across the sieve plates due to an electrical
potential difference between the upper and the
lower side of the sieve plate whereby the lower
side is more negative than the upper side i.e.
solutesmovefrom the uppersieve tubeelement
which is positively charged to the lower sieve
element which is negatively charged.
The electrical potential difference is maintained
across the plate by active pumping of positive
ions, mainly potassium ions, in an upward
direction. The energy used is produced by the
companion cells.
The movement of K+ ions through the pores of
the sieve plates rapidly draws molecules of
water and dissolved solutes through the sieve
pores, to enter the lower cell.
Evidence to support the electro-osmosis theory
1. K+ ions stimulate the loading of the phloem in
the leaves with sugars during photosynthesis.
2. Numerous mitochondria produce a lot of
energy for translocation, an indicator that
translocation is an active process. If however,
the phloem tissues are treated with a metabolic
poison, the rate of translocation reduces.

Cytoplasmic streaming
This suggests that the protoplasm circulates
using energy from sieve tubes elements or
companion cells through the sieve tube
elements from cell to cell via the sieve pores of
the sieve plates.
Asthe protoplasmcirculates,itcarries thewhole
range of the transported organic materials with
it. The solutes are moved in both directions
along the trans-cellular strands by peristaltic
waves of contraction, suchthat they move from
one sieve tube element to another usingenergy
in from of ATP. The proteins in the strands
contract in a wave form, pushing the solutes
from one sieve tube element to another, using
energy in form of ATP.
Diagram showing Cytoplasmic streaming
Criticism of the Cytoplasmic Streaming Theory
 Cytoplasmic streaming has not been
reported in mature sieve tube elements
but only in young sieve tubes.
 The rate at which the protoplasm
streams is far slower than the rate of
translocation
Transcellular strands/cytoplasmic strands
These are thought to be strands of protein which are
continuous from one sieve tube to the next passing
through the sieve plates. Theyare tubules and hence
enable the transport oforganic solutes in the phloem
being facilitated by peristalitic waves pressing along
them, using energy in form of ATP manufactured by
the companion cells and within the strands.
Evidence to support the transcellular strand
theory.
 The presence of transcellular strands in
the phloem.
 Mitochondria were observed in the
strands.
Surface spreading theory.

The mechanism suggests that solute molecules
might spread over the interface between the
different cytoplasmic materials just as oil
spreads at a water-air interface.
The molecular film, so formed, would be kept
moving by molecules being added at one end
and removed at the other end.
Loading and unloading sieve tubes
This explains the way in which sugars and other
productsof photosynthesisare carried from the
mesophyll into the sieve tubes in the leaves and
then removed from the sieve tubes in the roots
and other parts of the plant.
In some flowering plants e.g dicots, the sieve
tubes are surrounded by companion cells and
specialized parenchyma cells called transfer
cells.
The transfercellshaveirregularintuckingsof the
primary cell walls and plasma membranes. The
intuckings increase the surface area and bring
the plasma membrane close to the cytoplasm.
Transfer cells are responsible for moving the
products of photosynthesis e.g sugars from the
mesophyll cells into the sieve tubes. They also
carry water and salts from the xylem vessels to
the mesophyll cells and also to the sieve tubes.
In roots, storage organs and other growing
parts,transfercellsare responsiblefor removing
solutes (sugars and amino acids) from the sieve
tubes and move them to cells that need them.
Transfer cells are also found in metabolically
active parts of the plants and water secreting
glands ( hydathodes), secretory tissues inside
nectarines, in salt secreting glands, leaves of
halophytes ( salt brush).
Mechanism of transport of sucrose in plants.
 Sucrose is synthesized in the mesophyll
cells of the chloroplasts during the
process of photosynthesis.
 The sucrose solution is then actively
transported into the sieve tubes.
 The concentration of solutes in the sieve
tubes increases and water potential
decreases.
 Water is drawn from the xylem trachieds
and vessels into the sieve tubes of the
leaves by osmosis.
 Turgor pressure increases more than in
the roots and other parts of the plant
 In the roots andother partsof the plant,
sugars are transported out of the sieve
tubes, hence the turgor pressure
reduces.
 Sucrose is then transported from the
sieve tubes of the leaves where turgor
pressure is high to the sieve tubes of the
roots where turgor pressure is low.
Transport of sucrose from palisade
mesophyll to the sieve tubes of the
leaves
(The chemiosmotic theory of transport of
sucrose)
1) Sugars are transported from the mesophyll
cells to the transfer cells by the symplast
pathway and apoplast pathway.
2) Hydrogen ions from photolysis of water are
actively transported into the surrounding
transfer cells from the companion cells
(proton gradient is established).
3) The hydrogen ions then diffuse back to the
companion cells along the proton gradient
via the carrier proteins.
4) In the process of diffusion, the
protons/hydrogen ions carry along
themselves sucrose molecules into the
companion cells.

5) The solute concentration in the companion
cells increases and water is drawn into the
companion cells rapidly by osmosis.
6) A high hydrostatic pressure develops inside
the companion cells causing a mass flow of
sucrose solution into the sieve tubes through
the plasmodesmata. Sucrose is also actively
pumped from the cytoplasm of the companion
cells into the sieve tubes using energy in form of
ATP synthesized in the mitochondria of the
companion cells.
Qn a) Explain how sucrose is transported from;
i) The mesophyll cells to the
companion cells
ii) The mesophyll cells to sieve tubes
of the leaves
XYLEM TISSUE
Structure
 Consists of xylem vessels, xylem
tracheids, xylem fibres and pits. The
primary xylem consists of walls with
thickening which includes annular, spiral
and reticulate.
 The xylem and tracheids have walls
lignified, hollow and made of dead cells.
 The xylem pits lack lignin deposits
but have only primary cell walls. The pits
are for passage of water in to and out of
the lumen.
 The pits are boardered e.g in
conifers, the boardered pits have a plug
called torus/ valve which regulate the
passage of water.
 Xylem tracheids have tapering,
elongated tubes with sloping end walls
containing cellulose lined pits that allow
passage of water from cell to cell along
the narrow tubes.
 Xylem fibres are dead at maturity
and provide support and strength. They
are short,narrow and have much thicker
walls and overlapping end walls. The
thick and narrow lumens make them
suitable for additional mechanical
support to xylem. They do not conduct
water flow.
Development of xylem.
 The xylem is formed from meristematic cells
of the procambium.
 The cells of the procambium to the inside
divide mitotically to form a chain of
elongated cylindrical cells,placed endto end.
 During differentiation/ development, the
cellulose cell walls become deposited with
lignin and they become impermeable to
water and mineral salts and other solutes.
 The horizontal end walls completely break
down and one cell is then open to the next
cell.
 The protoplasmic contents (nucleus and
other organelles) also die off to form anopen
long lignified hollow tube called the xylem
vessel.
 The xylem vessel is perforated by numerous
pits on the wall.
 As the vessel continues to develop,
mechanical strength increase as a result of
spiral, annual, and reticulate thickening that
are laid down immediately inside the walls.
This prevent walls from curving in after loss
of protoplasm.
 Lignification/ thickening of xylem cell
 Lignification is the process of making cell
walls strong in plants by deposition of lignin.
It makes cell walls very strong. The lignin is
laid down in variety of patterns which are
shown below:

Difference between xylem vessels and xylem
tracheids
Xylem vessels Tracheids
 Is tubular/
cylindrical in
shape
 Are polygonal
in shape
 has wider
lumen
 Has narrow
lumen
 Has horizontal
end walls
 Has tapering
end walls
 Are relatively
larger
 are relatively
smaller
 Has thicker
walls
 Has relatively
thin walls
PHLOEM TISSUE
Structure
 The transportationof organic solutes usually
from leaves to other parts of the flowering
plant occurs in phloem tissue;
 Phloem is made up of sieve tube elements,
companion cells; phloem parenchyma and
phloem fibres.
Sieve tube elements
 Are long tube-like structures; arranged
longitudinally; and are associated with the
companion cells;
 Their end walls are perforated in a sieve-like
manner to form the sieve plates;
 A mature sieve element possesses a
peripheral cytoplasm and a largevacuole but
lacks a nucleus;
Companion cells
 Are specialized parenchymatous cells, which
are closely associated with sieve tube
elements;
 The sieve tubeelements and companion cells
are connected by pit fields present between
their common longitudinal walls; they have
all cell organelles including mitochondria,
nucleus, cell vacuoles, they are metabolically
active and all energy needed for
translocationin the sieve elements is derived
from here.
Phloem parenchyma
 Is made up of elongated;tapering; cylindrical
cells; which have dense cytoplasm and
nucleus;
 The cellwallis composed of cellulose;andhas
pits through which plasmodesmatal
connections exist between the cells;
Phloem fibres (bast fibres)
 Are made up of sclerenchymatous cells;
 These are muchelongated;unbranched;andhave
tapered apices;
 The cell wall of phloem fibres is quite thick;
 At maturity, the fibres lose their protoplasm and
die;
THE STRUCTURE OF THE STOMA
Each stoma consists of a pair of guard cells between
which a pore is formed when the stoma is open.
The endwalls of the guard cellsare unevenlythickened
whereby the inner walls are thick and inelastic, while
the outer walls are thin and elastic
The guard cells are nucleated and several small
chloroplasts are oftenpresent in the dense cytoplasm,
together with nucleus, sap vacuoles
STOMATAL CLOSURE AND OPENING
For most terrestrial plants, the stomata open
duringday and closes at night with exception of
xerophytes whose stomata closes during day
and open during night.
Stomatal closure and opening depends on
changes in turgor pressure of the guard cells.
When water osmotically enters into the guard
cells, the outer thin elastic walls expand
outwards and the thick inelastic inner walls
make the cells to bend. The inner walls of both

cells draw apart from each other and the pores
open.
The following theories have been advanced to
explain the process of opening and closure of
stomata:
a) The photosynthesis in the guard cells
b) The starch- sugar conversion/ pH theory
c) The potassium ion theory/ mineral ion
theory
Photosynthesis by the guard cells.
 According to this theory, during day, guard
cells carry out photosynthesis due to
presence of sunlight and sugars are
manufactured.
 The sugars lower the water potential of the
guard cells. The guard cells take up water by
osmosis and become turgid.
 The thin outer elastic walls are stretched
while the inner thick inelastic walls curve and
the stomata opens.
 At night, there is no light intensity and hence
no photosynthesis occurs in the guard cells,
no sugars are formed. More sugars are
utilized for respiration. The water potential
of the guard cells raises and water is lost into
the surrounding epidermal cells. The guard
cells become flaccid. The thick inner inelastic
walls straighten and the stomata closes.
The starch – sugar inter-conversion
 Suggests that stomata opens during day and
closes at night. During day, photosynthesis
occurs in the chloroplasts of the guard cells and
carbon dioxide is rapidly used up. This decreases
the acid concentration in the guard cells and
hence increases the pH
 In alkaline/ high pH, starch phosphorylase
enzyme converts starch into glucose which is
soluble.
 Accumulation of glucose decrease the water
potential of the guard cells and hence water
enters the guard cells from the surrounding
epidermal cells.
 The guard cells become turgid and the thin
elastic outer walls stretch outwards while the
thick inner inelastic walls curve and stomata
opens.
 During night, photosynthesis stops due to
absence of light. And carbon dioxide
accumulates in the intercellular air spaces of the
leaf. Carbon dioxide reacts with water in
presence of an enzyme carbonic anhydrase to
form weak carbonic acid. This lowers the pH in
the guard cells.
 In acidic pH, the enzyme starch phosphorylase
catalyzes the conversion of glucose/sugars back
into starch. This raises the water potential of the
guard cells. And water moves out of the guard
cells into the nearby epidermal cells by osmosis.
 The guard cells lose their turgidity and the inner
thick walls straighten and the stomata closes.
Alkaline pH
 Starch glucose/sugars
 Acidic pH
1. Mineral ion theory/ K+ theory
 Thistheory suggests that the stomata opens due
to changes in water potential of the guard cells
as a result of active transport of ions particularly
potassium ionsfrom neighboring epidermalcells.
 During day, the stoma opens because of active
pumping of potassium ions into the guard cells,
since sunlight activates ATPase enzymes and
leads to production of large amounts of ATP in
photophosphorylation.
 The hydrolysis of the ATPso formed provides the
necessary energy for active of potassium ions.
 Water potential of the guard cells
decreases/osmotic pressure increases due to
increased K+
ion concentration in the guard cells
and water moves into the guard cells byosmosis.
The thinner elastic walls stretch outwards and
the inner inelastic walls curve and stomata
opens.
 In darkness, potassium ions diffuse out of the
guard cells into the epidermal cells. The
concentration of the ions in the epidermal cells
increases and water is drawn rapidly into the
epidermal cells.
 Turgidity of the guard cells reducesand the thick
inelastic walls straighten. Stomata closes.

 At night, the stomata closes due to less or no
sunlight to activate ATPase enzymes and hence
no ATP is formed due to absence of
photophosphorylation. The potassium ion
concentration reducesdue to their diffusion out
of the guard cells into the neighboring epidermal
cells.
 This causes osmotic efflux of water from the
guard cellsto the epidermalcells, hence reducing
their turgidity, closing the stoma.
An illustration of the K+ concentration theory
It has however been observed that there are some
factors which make or induce the closure and
opening of the stomata, these include;
a Abscissic acid hormone(ABA) can make the
stomata to close.
b Insome plants, increase in the environmental
temperature above 250
c promotes the
closure of the stomata.
c Blue wavelength of light in the
electromagnetic spectrum induces opening
of the stomata.
d During water stress, like due to excessive
transpiration, stomata tends to close in
response to water deficit, irrespective of the
changes in light or carbon dioxide
concentration.
Question: Explainhow changesin turgidity occurto
cause opening of the stoma
Approach;
 High turgidity of the guard cells cause the
stoma to open. This arises when
photosynthesis occurs in the chloroplasts of
the guard cells to form sugars.
 More starch are converted into sugars due to
high pH.
 More ATP are formed where hydrolysis of
theseATPprovides energyfor active pumping
ofpotassiumionsintotheguardcells fromthe
surrounding epidermal cells.
 The water potential of the guard cells
lowers/osmotic pressure increases/solute
potential increases.
 This cause water ,olecules to be drawn from
thesurrounding epidermal cells intotheguard
cells rapidly by osmosis.
 Theguardcellsecometurgidandthethininner
walls stretch outwards wile the thick outer
walls curves and the stomata opens
TRANSPORT IN ANIMALS
Many materials including oxygen, carbon dioxide,
soluble food substances, hormones, urea e.t.c.need
to be transported from one point to another using a
transport network and medium.
The transport system in animals is mainly made up of
blood vessels consisting of blood as the medium
circulating through themto the various body tissues.
The transport systemis also made upof the pump i.e.
the heart which brings about circulation of blood
throughout the body, by pumping it. The transport
system is also composed of the lymph vessels
containing the lymph fluid.
The larger, compact and more active an organism is,
the more the need for a transport system due to a
small surface area to volume ratio which reducesthe
rate of diffusion of materials from the body surface
to the cells in the middle of the organism.

There are however some organisms which lack the
transport system e.g. protozoa and platyhelmithes
e.t.c. This is because, being small in size and being
flattened in shape gives these animals a large surface
area to volume ratio, this enables free and rapid
diffusion of materials from one part of the body to
another. Consequentlylarge multi-cellular organisms
have an elaborate transport system that carries
useful substances such as oxygenand glucose to the
cells and carries away the waste products of
metabolism. An elaborate transport system has two
major features;
i. An increased surface area of the sites of exchange
of materials. Suchsites include the lungs and the gills
where oxygen is absorbed and the villi of the ileum
where food nutrients are absorbed along the
alimentary canal.
ii. A system whereby the circulating medium carries
the absorbed substances at a faster rate than
diffusion. In some organisms with a blood circulating
system, blood flow is not confined to blood vessels
but instead it flows within a blood filled cavity called
Haemocoel e.g. in arthropods and molluscs.
In other organisms with the blood circulatory
system, blood flow is confined to blood vessels only
e.g. in vertebrates and some invertebrates such as
the earth worm.
Question:
1. Withexamples,explainthelackofspecialised
transport system in some organisms. (20
marks)
 Externally; these organisms have a large surface
area to volume ratio; hence diffusion alone is
adequate to meet their metabolic demands; and
exchange of materials occurs over the whole
body surface; for example
 Unicellular organisms like amoeba; are very
small;
 Flat worms (platyhelminthes); have flattened
bodies;
 Hydra; are hollow;
 Bryophytes; are small; and lack cuticle;
 Internally; the distance the materials have to
travel in suchanimals are small enough;for them
to move by diffusion alone; or cytoplasmic
streaming;
 Some organisms are not very active; hence their
metabolic wastes accumulate slowly; and can be
removed buy diffusion alone;
2. Explain the need of transport system and
respiratory pigments in some organisms. (15
marks)
 Some animals are large in size; with small surface
area to volume ratio; hence diffusion alone
cannot occur fast enough to meet their
metabolic demands;
 Internally; materials would have to travel longer
distances within the body;
 Some animals are also highly physically active;
and need metabolites delivered to; and waste
materials removed from cells; rapidly;
 In some animals, the body maybe covered with
impervious layers; that prevents the exchange of
materials directly diffusion;
 Respiratory pigments have a higher affinity of
respiratory gases; and thus larger amounts can
be transported;
IMPORTANCESOF A BLOOD CIRCULATORY SYSTEM
(FUNCTIONS OF BLOOD)
1. Tissue respiration
It enhancesthe formation of energyin the tissues by
transporting oxygenand soluble food substances to
the tissues to be used as raw materials for
respiration. Carbon dioxide is also transported away
from the tissues mainly in the form of bicarbonate
ions (HCO3-) as a by-product of respiration and then
taken to the lungs for its removal from the body.
Oxygen is transported in the form of oxy-
haemoglobin from the respiratory surfaces to the
tissues.
2. Hydration
Blood transports water from the gut to all tissues.
3. Nutrition
Blood transports the soluble well digested food
materials from the gut to the body tissues.

4. Excretion
Blood transports metabolic waste products from the
tissues to the excretory organs for their removal
from the body e.g. blood transports urea from the
liver to the kidney in order for it to be removed from
the body.
5. Temperature regulation
Blood distributes heat from the organs where it is
mainly generated e.g. the liver and the muscles,
uniformly throughout the body.
6. Maintenance of constant pH
Blood maintains a constant pH through the
maintenance of circulation of the plasma proteins
manufactured by the liver which act as buffers to
maintain the pH of the body fluids constant. This
enables enzymes to function efficiently as charges
will denature the enzyme.
7. Growth, development and co-ordination
Blood transport different metabolites such as
glucose, amino acids and hormones needed for the
growth and development of the body.
8. Defence
Blood defendsthe body against diseases throughthe
following ways;
a) By using some white blood cells (leucocytes)
which phagocytotically ingest and destroy
pathogens that cause diseases.
b. By formation of a blood clot around the wound so
as to prevent entry of microbes or pathogens into
the body.
c. By use of the immune response mechanism
towards infectione.g.byuse of the different typesof
antibodies to destroy the microbes.
Question: Explain the role of blood in defence
against diseases. (10 marks)
 Blood contains platelets; and clotting factors like
fibrinogen; which bring about blood clotting; to
prevent excessive blood; entry of pathogens; and
initiate wound healing;
 Blood contains phagocytes; like neutrophils and
monocytes; that engulf; and digest bacteria;
 Neutrophils also secrete interferon; that render
tissue cells resistant to viral attacks;
 Lymphocyteslike cytotoxic (T- killers) cells; attack
and destroy infected body cells;
 B – cells; produce antibodies; that neutralise
specific antigens;,coat bacteria;making it easyfor
the phagocytes to engulf them; (Look up the
immune system)
BLOOD
This is a highly specialized fluid tissue which consists
of different types of cells suspended in a pale yellow
fluid known as the blood plasma
BLOOD PLASMA
This is a pale yellow fluid component of blood
composed of the plasma proteins and blood serum
where the blood cells are suspended.
Blood plasma carries the biggest percentage of
blood and consists of a colourless fluid known as
serumand also plasma proteins. It is the blood serum
that all the different soluble materials are dissolved
e.g. urea, hormones, soluble food substances,
bicarbonate ions, respiratory gases e.t.c.
The plasma proteins are manufactured by the liver
and include the following;
a. Fibrinogen
Thisprotein is important for normal blood clotting by
changing into fibrin in the presence of thrombin
enzyme.
b. Prothrombin
This is the inactive form of the proteolytic enzyme,
thrombin, used in converting fibrinogen to fibrin
during the clotting of blood.
c. Globulin
Both Prothrombin and globulin play important roles
in the homeostasis. All the plasma proteins maintain
pH of the body fluids constant by acting as buffers.

d. Blood cells
There are three main types of blood cells which
include;
 Erythrocytes (Red blood cells)
 Leucocytes (White blood cells)
 Platelets
Importance of blood plasma
 Contains inorganic salts for contraction of
muscles
 Transmission of impulses
 Maintenance of constant internal environment (
buffer action)
 Responsible for viscosity of blood
ERYTHROCYTES (Red blood cells)
These are small numerous bi-concave disc shaped
cells mainly important in transportation of oxygenas
oxyhaemoglobin from the respiratory surfaces e.g.
lungs and gives it to the tissues. Erythrocytes are
manufactured by the bone marrow in adult and by
the liver in the foetus.
Adaptations of erythrocytes
i. They have a bi-concave disc shape which
provides a large surface area that enhances
maximum diffusion of enough oxygen into
them.
ii. They lack a nucleus so as to provide enough
space for haemoglobin in order to carry a lot
of oxygen in form of oxyhaemoglobin.
iii. Theyhave a red pigment called haemoglobin
in their cytoplasm which has a high affinity
for oxygen and therefore rapidly transports
oxygen.
iv. They have a thin and permeable membrane
which enables faster diffusion of oxygenand
carbon dioxide into them.
v. They have an enzyme known as carbonic
anhydrase within their cytoplasm which
enables most of the carbon dioxide to be
transported in form of bicarbonate ions
(HCO3-),by catalyzing the reactions between
carbon dioxide and water to from carbonic
acid.
CO2 + H2O H2CO3
vi. They have a pliable membrane (flexible
membrane) which can enable them change
their original shape and squeeze themselves
into the blood capillaries in orderto allow the
exchange of respiratory gases.
Diagram of the structure of red blood cells
NOTE; Erythrocytes have a life span of 120 days.
LEUCOCYTES (white blood cells)
They are amoeboid cells having a nucleus and a
colourless cytoplasm important for defense of the
body against infections. They are fewer than
erythrocytes i.e. they are about 7000/m3 of blood.
They are mainly manufactured by the bone marrow.
Theyare classifiedinto two main types whichinclude;
a. Granulocytes
b. Agranulocytes
a) Granulocytes (polymorphonuclear leucocytes)
These are leucocytes with granules in there
cytoplasm and a lobed nucleus. They originate in
bone marrow. There are three types of granular
leucocytes which include;
i. Basophils (0.5%)
ii. Eosinophils (1.5%)
iii. Neutrophils (70%)
Basophils (0.5%) produce heparin and histamine.
Heparin is an anti-coagulant which prevents blood
clotting in blood vessels. Histamine is a substance

that is released during allergic reactions e.g. hay
fever. Histamine brings about allergic reactions by
causing dilation (widening) and increased
permeability of small blood vessels which results in
such symptoms as itching,, localized swellings,
sneezing, running nose, red eyes e.t.c.
Eosinophils (1.5%) possess anti-histamine properties
and their number increases in people with allergic
reactions such as high fever, asthma e.t.c. so as to
combat the effects of histamine.
Neutrophils (phagocytes) (70%) engulf pathogens
phagocytotically and digest them actively inside to
defend the body against diseases.
b) Agranulocytes (mononuclear leucocytes)
These are leucocytes with no granules in there
cytoplasm usually with a spherical or bean shaped
nucleus. They originate in bone marrow and lymph
nodes. They are divided into two types;
i. Monocytes (4%)
ii. Lymphocytes (24%)
Monocytes (4%) are leucocytes which enter the
tissues from which they develop into macrophages
which carry out Phagocytosis to defend the body
against pathogens.
They have a bean shaped nucleus.
Lymphocytes (24%) theyare produced in the thymus
gland and lymph nodes. The precursor cells of
lymphocytes inthe bone marrow form a tissue which
is called the lymphoid tissue. Lymphocytes are
usually round and theypossess asmall quantityof the
cytoplasm. Lymphocytes produce antibodies,
agglutins, lysins, opsonins and antibodies.
Function of White Blood Cells
They defend the body against disease causing
organisms (antigens) by producing antibodies. The
antibodies defend the body by:
i) Agglutination:
Some antibodies have many binding sites and can
join the antigensof many differentpathogens. In this
way, the
pathogens can be joined together in clumps making
them vulnerable to attack from other types of
antibody.
ii) Precipitation:
Some antibodies bind together soluble antigens into
large units which are thus precipitated out of
solution. As such,
they are more easily ingested by phagocytes.
iii) Neutralization:
Certain antibodies bind toxic molecules produced by
pathogens and in doing neutralize their harmful
effects.
iv) Opsonisation:
Antibodies bind cellsurface antigens onbacteria cells
and make them more susceptible to being digested
by phagocytes.
v) Lysis:
Some breakdown pathogens’ membranes and cell
walls if they have them leading to water getting into
it by Pinocytosis. The pathogens swell and burst in
the process called lysis. Theyalso defendthe body by
engulfing foreign materials
(phagocytosis/endocytosis).
NB: The numberof white blood cells increasesduring
infection because the body manufactures more
white blood cells to attack the disease causing
organisms and prevent the infection from
proceeding. toxins.
BLOOD PLATELETS (thrombocytes)
These are irregularly shaped, membrane bound cell
fragments lacking the nuclei and are formed from
the bone marrow cells. They are responsible for

starting up the process of blood clotting. There are
abound 250,000 blood
The Process of Blood Clotting
Blood clotting is brought about by a soluble plasma
protein called fibrinogen when it is converted to an
insoluble form called fibrin.
The process begins when platelets exposedto air at
the injured part break down releasing
Thromboplastin.
Thromboplastin converts prothrombin to thrombin
in presence of calcium ions and vitamin K.
Thrombin is an enzyme which catalyzes the
conversion of fibrinogento fibrin which fibrin forms
a mesh that forms the blood clot. (Use the acronym
TPTFFtorememberthesequencewith PtoT occurring
in presence of calcium ions and vitamin K) platelets
per mm3 of blood.
TRANSPORT OF OXYGEN
The equation below shows how haemoglobin
combines with oxygen.
Hb + 4O2 ↔ HbO8
As shown by the equation above, each haem group
combines with one oxygenmolecule and therefore 1
haemoglobin molecule carries four oxygen
molecules.
HAEMOGLOBIN
 Haemoglobin is a large circular/oval
shaped/spherical and complex molecule that is
composed of four polypeptide chains (therefore
it has a quaternary structure) arranged around
four haem groups.
 Two of the polypeptide chains of the protein
globin are coiled to form α-helix,and this in turn
is folded on itself into a roughly spherical shape,
the other two chains are called β-chains due to
unique primary structures in both types of
chains.
 Various kinds of chemical bonds, together with
electrostatic attraction, keep the folds of the
chain together and maintain the shape of the
molecule.
 Haemoglobin is an example of a conjugated
protein: attached to the hydrophobic crevice of
the polypeptide chain is a flat group of atoms,
the prosthetic group, consisting of a central iron
atom held by rings of nitrogen atoms, which are
part of a large structure known as porphyrin
rings.
The prosthetic group is haem and it is to the iron
atom in the middle of it that the oxygen molecule
becomes attached. The presence of four haem
groups means that a single molecule ofhaemoglobin
can carry four molecules of oxygen. Haem belongs
to a class of organic compounds known as the
porphyrins.
Diagramshowing the structure of haemoglobin and
a haem group
Assignement;

a. With the aid of a diagram, describe
the structure of the haemoglobin molecule
Approach
It’s an oval, spherical or circular conjugated protein;
composed of globin protein and four haem groups
which are also prothetic groups; globin protein is
composed of four polypeptide chains; which are two
alpha and two beta polypeptide chains; each haem
group has iron(ii) ions;
b. How is haemoglobin adapted to its
function.
Qn: State three advantages of packaging the
haemoglobin into the red blood cells (3 marks)
 It does not alter the osmotic pressure of
blood since it is soluble.
 It enables other substances to be carried in
blood
 It does not interfere with the biochemical
reactions that occur in the plasma.
MYGLOBIN
Myglobin is another respiratory pigment, it consists
of a single polypeptide chain compared to the four of
haemoglobin. It stores oxygen in form of
oxymyoglobin in resting tissues.
It occurs largely in skeletal muscles/ voluntary
muscles of vertebrates and it gives meat the
characteristic red colour.
The significance of myglobin is that it has a higher
affinity for oxygen than haemoglobin and therefore
its dissociation curve is displaced to the left of that of
heamoglobin.
Ifmuscular activity persists, the myoglobin reserve of
oxygenis also exhaustedand the muscles undergoes
`oxygen debt` during which the muscle is respiring
mainly anaerobically and lactic acid is formed.
Once the activity ceases, the myoglobin reservesare
replenished from oxy-hemoglobin of blood. Lactic
acid is transported to the liver where it is broken
down.
There is a very high concentration of myoglobin in
muscles of diving mammals, sprinting mammals and
in flight muscles hence the meat of such mammals is
red. Non flight birds` meat is white in colour because
their muscles are less active and therefore no need
for storage of oxygen.
Qn Distinguish between hemoglobin and
myoglobin.
Oxygen tension and oxyhaemoglobin formation
The ability of erythrocytes to carry oxygen to the
tissues is due to haemoglobin having a high affinity
for oxygen i.e. it can readily combine with oxygen
and becomes fully saturated with it at relatively low
partial pressures of the gas. Partial pressure of a gas
is the measure of the concentration of a gas
expressed in Kilo Pascals (Kpa) or milimetres of
mercury (mmHg)
The high affinity of haemoglobin for oxygen is
measured experimentally by determining the
percentage saturation of haemoglobin with oxygen.
When the percentage saturation of blood with
oxygen is plotted against the partial pressure of
oxygen an S-shaped curve or sigmoid curve is
obtained and this curve is called the oxygen
dissociation curve which is shown below.
The curve indicatesthat a slight increase inthe partial
pressure of oxygen leads to a relatively sharp/steep
increase in the percentage saturation of
haemoglobin with oxygen. This indicates that
haemoglobin has a high affinity for oxygen in that it
readily combines with it and become saturated with
it at low partial pressures of oxygen.

The S-shaped curve is due to the way in which
haemoglobin binds to oxygen. The first molecule of
oxygen combines with a haem group with difficulty
and distorts the shape of the haemoglobin molecule
during the process. The remaining three haem
groups bind with three oxygen molecules more
quickly than the first one which increases rapidly the
percentage saturation of haemoglobin with oxygen.
As the partial pressure of oxygen increases, the
percentage saturation of haemoglobin with oxygen
becomes constant because all the polypeptide
chains are saturated with oxygen molecules.
When oxyhaemoglobin is exposed to regions where
the partial pressure of oxygen is low, e.g. in the
respiring tissues, the first oxygen molecule is
released easily and faster but the last one is released
less readily with a lot of difficulty and least readily.
The steeppart of the curve corresponds to the range
of oxygen partial pressures found in the tissues.
Beyond this part of the curve, any small drop in
oxygenpartial pressure results into a relatively large
decrease in the percentage saturation of blood due
to the dissociation of oxyhaemoglobin to release
oxygen to the tissues. Beyond this part of the curve
any small drop in the oxygenpartial pressure results
into a relatively large decrease in the percentage
saturation of blood with oxygen, due to the
dissociation of oxyhaemoglobin to release oxygento
the tissues.
In conclusion, the curve indicates that haemoglobin
has a high affinity for oxygen where the oxygen
tension is high e.g. in the alveolar capillary of the
lungs. However, the affinity of haemoglobin for
oxygenis lower where the oxygen tension is low and
instead it dissociates to release oxygen e.g. in the
blood capillaries serving blood to respiring tissues.
Note; animals which burrow into oxygen-deficient
mud have haemoglobin which has a high affinity for
oxygen. The oxygen dissociation curve for the
lugworm is therefore situated to the left of human
blood.
Question:
The oxygen dissociation curve for adult human
haemoglobin is sigmoid.
(a) Explain why the curve is sigmoid. (10 marks)
Without oxygen;the haemoglobinmolecule is stable;
due to hydrogen bonds; ionic bonds; and
hydrophobic interactions; so the first oxygen
molecules attaches with difficulty;
However,when one of the chains acceptsan oxygen
molecule;the structure is altered; and the remaining
haem groups are exposed;so that the other oxygen
molecules are taken up more rapidly/ easily;
(b) Explain the significance of the sigmoid shape of
the curve. (06 marks)
Haemoglobin easily saturates with oxygen;whenthe
oxygenpartial pressures are high;for example in the
lungs;
A small decrease in partial pressure of oxygen;
causes a rapid release of oxygen from the
haemoglobin; so that the respiring tissues can use it;
Effect of carbon dioxide on the oxygen dissociation
curve (Bohr’s effect)
Within tissues there is a highconcentration of carbon
dioxide produced during aerobic respiration
C6H1206 + 6O2 6CO2 + 6H2O
Increase in carbon dioxide concentration decreases
the affinity of haemoglobin for oxygen, by making
the pH ofthe surrounding mediummore acidic(low),
therebyshifting the oxygendissociation curve to the
right. This shifting of the curve to the right is known
as Bohr’s effect i.e. the shifting of the oxygen
dissociation curve to the right due to the increase in
partial pressures of carbon dioxide whichresults into
haemoglobin having a low affinity for oxygen and a
high affinity for carbon dioxide.
Bohr’s effect may be defined as the lowering of the
affinity of blood’s haemoglobin for oxygen due to
increased acidity caused by increase in carbon dioxide
concentration.
From the dissociation curves below, shifting the
oxygen dissociation curve to the left means that
haemoglobin has a higher affinity for oxygen and
therefore becomes fully saturated with it at verylow

partial pressures of oxygen. It also means that
haemoglobin has a low rate ofdissociation to release
oxygen to the tissues but a high rate of combining
with oxygen.
Shifting of the oxygendissociation curve to the right
means that haemoglobin has a lower affinity for
oxygen and a higher rate of dissociation to release
oxygen to the tissues
Effect of carbon monoxide on the affinity of
haemoglobin for oxygen
There’s a loose and reversible reaction between
oxygenmoleculesandiron (II) atoms of haemgroups
of haemoglobin to from oxyhaemoglobin. This
means that iron (II) is not oxidized to iron (III) as
haemoglobin combines with oxygen.
In the presence of carbon monoxide and oxygen,
haemoglobin combines readily with carbon
monoxide to form a permanent compound known as
carboxyhaemoglobin rather than combining with
oxygen.
A permanent carboxyhaemoglobin compound is
formed because carbon monoxide oxidizes iron (II)
to iron (III). This reduces the free haemoglobin
molecules available to transport oxygen molecules
to the tissues, which makes the tissues develop
symptoms of anoxia (total lack of oxygen in the
tissues).
Therefore, carbon monoxide is referred to as a
respiratory poison because it can readily combine
with haemoglobin much more than oxygen and the
product formed i.e. carboxyhaemoglobin does not
dissociate.
Note; smokers have 10% of their total haemoglobin in
form of carboxyhaemoglobin.
Myoglobin and other pigments
Myoglobin is a respiratory pigment which also
contains iron containing haem groups mostly found
in the muscles where it remains fully saturated at
partial pressures below that required for
haemoglobin to give up its oxygen.
Myoglobin has a higher affinity for oxygen than
haemoglobin in a way that it combines readily with
haemoglobin and it becomes fully saturated with
oxygen at a lower partial pressure of oxygen.
Myoglobin acts as a store of oxygen in resting
muscles in form of oxymyoglobin and only releases
the oxygenit stores only when oxyhaemoglobin has
beenexhaustedi.e.manyvigorous activities because
myoglobin has a higher affinity for oxygen than
haemoglobin. The oxygen dissociation curves for

myoglobin lies to the left of that of haemoglobin as
shown in the graph below.
Note;
i. High affinity refers to low rate of dissociation to
release oxygen and a higher rate of association of
haemoglobin with oxygen.
ii. Low affinity refers to higher rate of dissociation to
release oxygen and a lower rate of association of
haemoglobin with oxygen.
iii. There are other respiratory pigments mostly
found in the lower animals which include
haemocyanin which consists of copper and mostly
found in some snails and crustaceans
iv. Other pigments include haemocrythrin which
contains iron and is also found in some in annelids
Chlorocruorin which also contains iron is also found
in some annelids.
Factors that lower the affinity of haemoglobin for
oxygen
 High partial pressure of carbon dioxide.
 Lower partial pressure of oxygen
 High core body temperature
 Low blood pH
Questions:
From the graph above, how is the saturation of
myglobin with oxygen be compared with that of
haemoglobin.
Approach;
Similarities;
 In both myoglobin and
haemoglobin,percentage saturation reaches
maximum
 In both myoglobin and haemoglobin,
percentage saturation increases to reach
maximum.
 In both myoglobin and haemoglobin, the
percentage saturation is a constant after the
maximum.
Differences
 Percentage saturation of myoglobin with
oxygen is higher while the percentage
saturation of haemoglobin with oxygen is
lower between o and 2 kpa
 Percentage saturation of myoglobin with
oxygen reached a maximun at lower partial
pressure of oxygen of approximately 1.5kpa
while maximum saturation of haemoglobin
with oxygenreached a maximum at a higher
partial pressure of approximately 4.5 kpa of
oxygen.
 The saturation of myoglobin with oxygen
increases rapidly while the saturation of
haemoglobin with oxygen increases
gradually between 0 and approximately
1.2kpa.
 Percentage saturation of haemoglobin with
oxygen increases gradually while saturation
of myoglobin with oxygen remains constant
between 2 and 5 kpa.
 The maximum saturation of myoglobin with
oxygen is higher than the percentage
saturation of haemoglobin with oxygen.
Comparison betweenthe oxygendissociation curve
for Lugworms’ haemoglobin and that of Man
The oxygen dissociation curve of the lugworm’s
haemoglobin lies on the left of that of man’s
haemoglobin as shown in the graph below;

This indicates that the haemoglobin of the lugworm
has a higheraffinity for oxygenthanthat of man.This
is because the lugworm lives in oxygendeficientmud
and so in order to extract enough oxygen from that
environment of low oxygen tension, the
haemoglobin of the lugworm must have a higher
affinity for oxygenthan that of man thriving in a well
supplied environment with oxygen.
This implies that the lugworm’s haemoglobin
dissociates to release oxygento its tissues compared
to that of man which makes the lugworm less active
than man, who releases much oxygen rapidly to the
tissues.
Comparison between the oxygen dissociation
curves of different sized mammals
Small animals have higher metabolic rates and so
need more oxygen per gram of tissue than larger
animals. Therefore they have blood that gives up
oxygenmore readily i.e.their dissociation curvesare
on the right of the larger animals.
Comparison between the oxygen dissociation
curves at rest and during exercise
During exercise, the oxyhaemoglobin releases
oxygen more readily hence the oxygen dissociation
curve during exercise isto the right of that whenthe
individual is at the right of the curve when at rest.
Advantages of regular exercise
1. Improves the efficiency of the ventilation
mechanism
2. Strengthens the respiratory muscles
3. Improves blood supply to the lungs
4. Increases the ability of the blood vessels to
extract oxygen from the alveoli
5. Increasesthe blood volume and total number of
blood cells
6. The heart becomes harmlessly enlarged.
7. It lowers the resting pulse of the heart which
indicates a more efficient transport system.
8. Improves the ability of the respiring tissues to
generate and use energy due to increased number of
mitochondria with a high concentration of respiratory
enzyme.
9. It leads increased intake of water to clean body
systems.
Question
Describethe changesthat occur to the heartrateand
circulatory system during a 100m race. (13 marks)
a) The metabolic rate increases especially in the
skeletal muscles to provide energy;
b) Increased carbon dioxide; and heat; production
in these regions promote local vasodilation;
c) The carbon dioxide in blood is detected by the
chemoreceptorsin the aorta; and carotid bodies;
which in turn stimulate the vasomotor centre;to
promote vasoconstriction elsewhere inthe body;
this increases the blood pressure; which speeds
up blood flow;

d) The heartrate also increases;and more complete
emptying of the ventricles occurs;
e) Towards the end of the race, the muscles respire
anaerobically; and produce lactic acid; strong
muscles contractions occurs to squeeze veins
and promote faster venous return to the heart;
Comparison betweenthe oxygendissociation curve
of maternal haemoglobin and that of the foetal
haemoglobin
The oxygendissociation curve of foetal haemoglobin
lies to the left of maternal haemoglobin as shown in
the diagram below;
This indicates that the foetal hemoglobin has a
higher affinity for oxygen than that of an adult
human being.Thisenablesthe foetal haemoglobin to
pick sufficient oxygen from the mother via the
placenta and also increases on the oxygen carrying
capacity to the tissues, especially when the foetus
needs a lot of energy.
It also increases on the oxygen carrying capacity to
the tissues of the foetus in the situation whereby
deoxygenatedand oxygenated blood are mixed due
to the bypasses of ductus arteriosus and foramen
ovale in the foetus.
Effect of changing altitude on oxygen carriage
There is a decrease in the partial pressure of oxygen
in the atmosphere with increase in altitude from sea
level. Therefore the volume of oxygenis less at high
altitudes than at sea level. When an organism moves
from the sealevel to high altitudes, very fast, suchan
organism tendsto developsymptoms of anoxia (lack
of oxygen) which include headache,fatigue, nausea,
and becoming unconscious
However, when an organism moves slowly from sea
level to high altitudes like the mountain climbers,
such an organism can at first develop symptoms of
anoxia but later on such symptoms disappear due to
adjustments in the respiratory and circulatory
systems in response to insufficient oxygen reaching
the tissues from the surrounding.
The amount of haemoglobin and the red blood cell
count increases together with the rate of breathing
and the heart beat. More red blood cell formation
occurs in the bone marrow under the control of the
hormone called erythropoietin secreted by the
kidney.
Secretion of erythropoietin is stimulated by lower
oxygentensionin the tissues.Increase in the amount
of haemoglobin and red blood cells, together with
increase in the breathing rate and heart beat
increases the oxygen carrying capacity of the blood
to the tissues which leads to the disappearance of
the symptoms of anoxia and which also makes the
individual organism to be acclimatized.
Acclimatization is therefore a condition whereby an
organism carries out a series of physiological
adjustments in moving from a low altitude area to a
high one to avoid symptoms of anoxia so that such
an organism can survive in an environment of low
oxygen content.
The graphs below show the oxygen dissociation
curves of people living at sea level and at high
altitude

The mammals that live in regions of the world
beyond the sea level e.g. mountains solve the
problem of lack of enoughoxygeninthe atmosphere
by possessing haemoglobin with a higher affinity for
oxygen than that of mammals at sea level. This
enables the high altitude mammals to obtain enough
oxygen through the oxygen deficient environment
e.g. the llama. This explain why the oxygen
dissociation curve of the haemoglobin of the llama
lies to the left of that of other mammals at sea level
e.g. the horse as shown below;
How individuals become acclimatised to high
altitudes.
1. At high altitudes the partial pressure of oxygenis
low; deeper breathing (hyperventilation) takes
place;to increase the amount ofoxygenreaching
the lungs;
2. Deeper breathing removes more carbon dioxide
than produced; and the blood pH rises; more
hydrogen carbonate ions are removed by the
kidney to restore blood pH to normal;
3. Improved capillary network in the lungs; to
absorb more oxygen;
4. Increasedred blood cell count;and haemoglobin
concentration in the red blood cells; to carry
more oxygen;
5. Increasedmyoglobin levelsin the muscles;due to
its high affinity for oxygen; more oxygen can be
stored and later exchanged with tissues.
Effect of temperature on haemoglobin oxygen
dissociation curve
A rise in temperature lowers the affinity of
haemoglobin for oxygen thus causing unloading
from the pigment i.e.a rise in temperature increases
the rate of dissociation of oxyhaemoglobin to
release oxygen to the tissues.
Increased tissue respiration which occurs in the
skeletal musclesduring exercise generates heat.The
subsequentrise in temperature causesthe release of
extra oxygenfrom the blood to the tissues. Thisis so
because increase in temperature makes the bonds
which bind haemoglobin with oxygen to break,
resulting into the dissociation of oxyhaemoglobin
Oxygen dissociation curve for haemoglobin at
different temperatures
A rise in temperature lowers the affinity of
haemoglobin for oxygen thus causing unloading
from the pigment i.e.a rise in temperature increases
the rate of dissociation of oxyhaemoglobin to
release oxygen to the tissues.
Increased tissue respiration which occurs in the
skeletal musclesduring exercise generatesheat.The
subsequentrise in temperature causesthe release of
extra oxygenfrom the blood to the tissues. Thisis so
because increase in temperature makes the bonds
which combine haemoglobin with oxygen to break.
Oxygen dissociation curve for haemoglobin at
different temperatures
TRANSPORT OF CARBON DIOXIDE
Carbon dioxide is transported from the body tissues
mainly inform of bi-carbonate ions in blood plasma to
the lungs for removal.
Although carbon dioxide is mainly transported
inform of bi-carbonate ions i.e. 85%, carbon dioxide
can also be transported in the following ways;
a) About 5% of carbon dioxide is transported in
solution form. Most of the carbon dioxide
carried in this way is transported in physical
solution. A very small amount is carried as
carbonic acid. In the absence of
haemoglobin, the plasma proteins bufferthe
hydrogenions to form weak proteionic acids.
b) About 10% of carbon dioxide combines with
the amino group of haemoglobin to form a

neutral compound known as carbamino
haemoglobin (HbCO2). If less oxygenisbeing
carried by haemoglobin molecule, thenmore
carbon dioxide is carried in this way as
HbCO2.
c) About 70% -85% of the carbon dioxide is
transported in the blood plasma in form of
bicarbonate ions,
Question: Explain the role of carbon monoxide as a
respiratory poison. (07 marks)
 Haemoglobin has a high affinity for carbon
monoxide compared to oxygen; and combines
irreversibly with it; forming a stable
carboxyhaemoglobin molecule; that prevents
the carriage of oxygen to the respiring tissues;
 Without oxygen,tissuescannot respire; and thus
lack energy to keep the cells alive; leading to
death of the victim;
Transportation of carbon dioxide inform of
hydrogen carbonate ions
When carbon dioxide is formed during respiration, it
diffuses from the tissues into the erythrocytes, via
their thin and permeable membrane. Inside the
erythrocytes,carbon dioxide reacts with water inthe
presence of carbonic anhydrase enzyme to form
carbonic acid as shown below;
H2CO3 (aq) H+ + HCO-3( aq)
The formed carbonic acid then dissociates into
hydrogen ions and bicarbonate ions as shown below
The formed hydrogen ions decrease the pH in
erythrocytes which results into the dissociation of
oxyhaemoglobin being carried from the lungs to the
tissues into the free haemoglobin molecules as free
oxygen molecules.
HbO8 Hb + 4O2 (g)
The free oxygenmolecules diffuse into the tissues to
be used in respiration. The free haemoglobin
molecules buffer the hydrogen ions (H+) inside the
red blood cells into a weak acid known as
haemoglobinic acid
In case of excess H+ plasma proteins are used to
buffer them into another weak acid called proteinic
acid.
The formed hydrogen carbonate ions within the
erythrocytes diffuse out into the plasma along the
concentration gradient and combine with sodium to
form sodium hydrogen carbonate which is then
taken to the lungs.
The outward movement of bicarbonate ions from
the erythrocytes into the plasma results into an
imbalance of positively charged and negatively
charged ions within the cytoplasm.
In order to maintain electrochemical neutrality, to
remove this imbalance in the redblood cells,chloride
ions diffuse from the plasma into the red blood cells,
a phenomenon known as the chloride shift
When the bicarbonate ions reach the lungs, they
react with H+ to form carbonic acid which eventually
dissociates into carbon dioxide and water.
H+ + HCO3- H2CO3
H2CO3- H2O + CO2
The carbon dioxide and water formed from the
dissociation ofcarbonic acidin the lung capillaries are
then expelled out by the lungs during exhalation so
as to maintain the blood pH constant

Question: Describe how carbon dioxide in blood is
expelled as gaseous carbon dioxide into the lungs.
(06 marks)
 Haemoglobinic acid reaches the lungs and takes
up oxygen to form oxyhaemoglobin; while
releasing hydrogen ions;
 Hydrogen ions combine with hydrogen
carbonate in the RBC to form carbonic acid;
which dissociates in to carbon dioxide and water;
catalysed by carbonic anhydrase;
 Carbon dioxide diffuses out of the RBCs into the
lungs;
VASCULAR SYSTEMS IN ANIMALS
In animals, every vascular system has at least three
distinct characteristics.
a. It has a circulating fluid e.g. blood
b. It has a pumping device inform of a
modified blood vessel or a heart.
c. It has tubes through which the fluid can
circulate e.g. blood vessels
Question: 1. Explain the role of a blood vascular
system in animals. (05 marks)
To provide a rapid; mass flow; of materials from one
part of the body to another; over long distances;
where diffusion would be inadequate;
2. Describe the characteristics of the blood vascular
system. (08 marks)
A circulating fluid; the blood;
A contractile pumping device; which is the heart in
some animals; or a modified blood vessel;
Vessels through which blood passes; which can be
tubular blood vessels; or sinuses;
Transverse section through the insect’s heart
Note: animals require a transport systembecause of;
 Surface area of the organism
 Surface area: volume ratio of the organism
 Activity of the organism
 The diffusion distance for the transported
substances betweenthe tissues to and from
their sources.
There are two types of vascular systems, the open
vascular system and the closed vascular system.
Open vascular system
Open circulation is the flow of blood through the
body cavities called Haemocoel instead of flowing in
blood vessels. This exists in most arthropods,
molluscs and tunicates.
In this system, blood is pumped by an aorta which
branches into a number of arteries which open into
the haemocoel. From the haemocoel, blood under
low pressure moves slowly to the tissues where
there’s exchange of materials e.g. gases, nutrients
e.t.c and blood percolates back into the heart via the
open ended veins. Sucha system may be referred to
as a Lacinar system.
Features of an open circulatory system
1. Blood is not contained in blood vessels but also
flows in the haemocoel
2. Blood gets into direct contact with the body
cells
3. Blood flows under low pressure
4. Blood does not transport respiratory gases
5. There is poor control of blood distribution

In insects the haemocoel is divided into two parts by
a transverse pericardial membrane forming a
pericardialcavitydorsally and the ventralperivisceral
cavity. In the body of the insects there are no blood
vessels exceptthe tubular heart which is suspended
in the pericardial cavity by slender ligaments and
extendsthrough the thorax and abdomen.The heart
is expanded in each segment to form a total of 13
small chambers which are pierced by a pair of tiny
tubes called ostia. The ostia allow blood to flow from
one segment of the chamber to another. Alary
muscles are located at each chamber of the heart.
Mechanism of single open circulation in insects
Blood flows through the heart from the
posterior end to the anterior end by waves of
contractions (systole) which begin from the
posterior end and proceed to the anterior end.
These waves of contractions enable blood to
flow through the heart and then enter the
perivisceral cavity.
During systole, the heart muscles relax and the
heart contracts. Blood is propelled forward
throughthe heart by waves of contraction from
the posterior to the anterior. Blood then leaves
the heart and enters the haemocoel.
During diastole, the alary muscles contract
which increases the volume of the heart and
reduces thepressureat the same time. The drop
in pressure leads to movement of blood from
the haemocoel throughthe ostia into the heart.
Contraction of the alary muscles also has the
effect of pulling the pericardial membrane
downwards, thereby raising the blood pressure
in the perivisceral cavity and decreasing it in the
pericardial cavity, hence blood flows into the
pericardial cavity. The heart chambers are
equipped with valves which allow blood to
enter, but not to leave, the heart throughthem.
Advantages of an open circulatory system.
1. Animals are less vulnerable to pressure
changes;which allows some of them like the
molluscs to live at great depth; since their
bodies cannot be compressed;
2. Gives animals greater control of their body
temperature; by easily dissipating off heat;
allowing insects to survive extremely hot
conditions;
3. Blood requires less energy for distribution;
since it occurs at low pressure;
4. In insects the blood does not carry
respiratory gases; hence damage to the
system does not disrupt their movement in
and out the body
Disadvantages of an open circulatory system.
1. It is only suitable for small organisms;where
bloodtravelsshortdistances;as it is pumped
at low pressure;
2. There is poor control of blood distribution;
which deprives vital organism of blood;
during times of urgency;
3. Suitable for less active organisms;where the
metabolic requirements are low; which
results in slow movement; and adaptability
to new environments;
Closed vascular system
In a closed vascularsystem,blood flows in blood
vessels or sinuses. It occurs in all vertebrates,
annelids such as earthworms, cephalopods and
echinoderms.
The distribution of blood in this system is
therefore adjustablee.g. blood from theheart is
at high pressure and that to the heart is at low
pressure. Closed vascular systems are further
divided into single and double circulation.
Features of a Closed blood circulatory system
1. Blood is confined to blood vessels;
2. Blood does not get into direct contact
with cells;
3. Blood flows at a high pressure;
4. Transports respiratory gases;

5. Distribution of blood is well controlled
according to the demands of the body;
Advantages of a closed circulatory system.
1. Due to high pressureinvolved; there is more
efficient delivery; and removal of materials;
to and from the tissues; since blood travels
faster;
2. It alsoallowsorganismstoattainlargersizes;
since blood can travel longer distances;
3. Allows higher metabolic rates; and hence
activity in animals due; to its efficiency in
terms of delivery of metabolites to and
removal of wastes from the tissues
4. There is greater control of the blood
distribution; hence better body functioning
when there is urgent need of materials to
specific organs;
5. Pulmonary and systematic circulation like in
mammals and birds can maintain their
separate pressures as required by the body;
Disadvantages of closed circulatory system.
1. The system is linked with many other
systems; such as respiratory and excretory
system; and damage to it disrupts many
other processes;
2. Blood is transported at high pressure; and
requires more energy to maintain;
3. There is need to control the pressure in the
system; asany deviationsfrom the normmay
lead to death of the individual
A. Single and double circulation
Single circulation is the flow of blood through
the heart once for every complete circulation
aroundthe body. Single circulation occurs in fish
and the deoxygenated blood from the body
tissues is pumped by the heart to the gills from
where it flows back to the body tissues and
eventually returns to the heart.
Disadvantages of single circulation
In fish, blood passes through the capillary
system before returning to the heart i.e the
capillaries of the gills and those of the body.
Capillaries offer resistance to blood flow, this
resultsinlowering in theblood pressure.Forthis
reason, blood flow tends to be sluggish on the
venous side. Back flow of blood occurs and
these impose severe limitations on the activities
of many fishes.
Flow of blood under low pressure is the main
cause of back flow of bloodandthis is overcome
by any of the following:
 In fish, the veins are replaced with large
sinuses thatoffur minimum resistance to
blood flow.
 In mammals, the problem is solved by
development of double circulation.
 Possession of two separate hearts, one
for pumping blood to the body, other for
pumping blood to respiratory organs e.g
octopus and squids.
Question: Explain the problems associated with
single circulatory system in those animals that
possess it. (08 marks)
 Blood passesthroughtwo capillary systems;
that of the gills; and the rest of the body;
before returningto the heart;which leadsto
a decrease in pressure; as capillaries offer
much more resistance to blood flow;
 Consequently, venous blood return is slow;
and imposes severe limitations on the
activities of the fish;
Explain how the problems associated with a
single circulatory system have been solved in;
(i) Organisms that possess it. (03 marks)
Veins are replaced with large sinuses; that offer
less resistance to blood flow; hence blood can
flow much faster;
(ii) Molluscs. (06 marks)

Molluscs have the main heart; that pumps
oxygenated blood to all the body organs; and a
pair branchial hearts; that pump deoxygenated
blood to the gills;
They have large sinuses instead of veins; which
offer minimum resistance to blood flowing back
to the heart;
(iii) Mammals. (06 marks)
 Development of a double circulatorysystem;
where deoxygenatedbloodis pumpedto the
lungs; oxygenated blood returns to the
heart; and is then pumped to the rest of the
body
 The heart is divided into the right and left
sides; to prevent mixing of oxygenated and
deoxygenated blood;
Diagram showing single circulation in fish
B. Double circulation
Double circulation is the flow of blood through
the heart twice for every complete circulation
around the body.
In double circulation deoxygenated blood from
body tissues is pumped from the heart to the
lungs from where it returns to the heart after
being oxygenated and it is then re-pumped to
the body tissues so as to supply oxygen to the
body tissues. A double circulation serves as one
of the solutions towards the sluggish flow of
blood at the venous side in single circulation.
In double circulation, the heart must be divided
into the left and right chambers to prevent
oxygenated blood from mixing with
deoxygenated blood e.g. in reptiles, birds and
mammalshave a four chamberedheart made up
of the rightatrium and ventricle andthe left and
atrium and ventricle.
The frog experiences double circulation
although its heart has three chambers namely;
one ventricle and the two atria i.e. the left and
right atria. Both deoxygenated and oxygenated
blood in the frog flow through the same
ventricle and conus arteriosus at the same time
without mixing. This is achieved due to the
folding in the walls of the ventricle which
enhancestheseparationof deoxygenated blood
from oxygenated blood and this separation is
also facilitated by the spinal valves in the conus
arteriosus.
Diagram showing double circulation in a frog and a
mammal
Some organisms e.g. the octopus and squids
solve the problem of sluggish flow of blood of
the venous side by possessing brachial hearts
which pumpdeoxygenatedbloodfrom the body
tissues of the gills and eventually back to the
main heart. The main heart pumps, oxygenated
blood to body tissues from the gills.
How blood circulation in insects differs from the blood
circulation in man

Question: Explain blood circulation of an insect
(o8 marks)
Approach:
Insect blood circulation is an open and single
blood circulation.
 For the blood to bedrawn into the heart from
the haemocoel of the pericardial cavity, the
alary muscles contract to pull the pericardial
membranedownwards. This exerts tension in
the heart ligaments and the heart expands
 The internal pressure within the heart is
reduced below external pressure and blood
enters into the heart via the open ostia.
 Blood also flows from the perivisceral cavity
into the pericardial cavity due to higher
pressure in the perivisceral cavity than the
pericardial cavity.
 Relaxation of the alary muscles causes the
tension on the heart ligaments to be eased.
The heart contract and the pressure in the
heartincreases morethan that of the external
pressure causing the blood to flow from the
heart to the haemocoel via the aorta
Differences in circulatory systems in fish and
mammals
Fish Mammals
 Blood in the heart
flows through one
atrium and one
ventricle.
 Blood in the heart
flows through
two atria and two
ventricles
 Deoxygenated
blood leavesthe
heart viaaorta
 oxygenated
blood leaves the
heartvia theaorta
 Single blood
circulation
 Double circulation
 Blood flows under
low pressure
 Blood flowsunder
high pressure and
speed
 Oxygenation of
blood occurs
 Oxygenation of
blood occurs in
occurs in the gill
lamellae
the lung
capillaries
 The heart contains
and pumps only
oxygenated blood
 The heart
contains and
pumps both
oxygenated and
deoxygenated
blood
Question: What advantages are there in
supplyingthe pulmonary circulation with blood
at lower pressure than that of the systemic
circulation? (08 marks)
 Oxygenated blood of the systemic
circulation should reach body capillaries far
away from the heart; at a much higher
pressure;which is essentialfor the formation
of tissue fluid; and efficient functioning of
the organs; as oxygen and metabolites are
quickly delivered to the tissue cells; which
permits high metabolic rates;
 A lower pressure in the pulmonary
circulation prevents rupture of the delicate
pulmonarycapillaries; which are foundin the
lungs that are near the heart;
Blood circulation in
insects
Blood circulation in man
Blood flows through the
heart once for every
complete circuit around
the body
Blood flows through the
heart twice for every
complete circuit around the
body
Blood gets into contact
with the body cells
Blood does not get into
direct contact with body
cells
Blood does not carry
respiratory gases
Blood carries respiratory
gases
Blood does not contain
respiratory pigments
Blood contains
haemoglobin as a
respiratory pigment
Blood flows under low
pressure
Blood flows under high
pressure
Blood distribution is
poorly controlled
Blood distribution in body is
well controlled
Blood flows in an open
cavity
Blood is confined in blood
vessels
Blood is pumped by a
tubular heart with many
chambers
Blood is pumped by a four
chambered heart

MAMMALIAN BLOOD CIRCULATION
The mammalian blood circulation is a double
blood circulation which is mainly based on the
heart and blood vessels,
BLOOD VESSELS
There are three main types of blood vessels;
arteries, veins andcapillaries. The walls of these
blood vessels occur in three layers, namely;
a. Tunica externa (outer most layer)
b. Tunica media (middle layer)
c. Tunica interna (inner most layer
Tunica externa, this is the outermost layer
which is tough and made up of thick collagen
fibres which provide strength and prevents
extensive stretching.
Tunica media is the middle layer which consists
of smooth muscles, collagen and elastic fibres.
The structural proteins allow for the stretching
of the walls of blood vessels during vaso-
dilation. The smooth muscles allow for the
distension and constriction of the walls of the
blood vessels.
Tunica interna is the innermost layer composed
of a single layer of squamous endothelium. It is
found in all walls of blood vessels. Capillaries
have only the tunica interna.
Diagrams showing the transverse sections of
the vein, artery and capillary
Comparison between arteries and veins
Both tunica media and tunica externa are more
developed in arteries than veins and therefore
arteries have thicker walls than those of veins.
Arteries have thicker walls than veins because
blood flows through them at a higher pressure
than in the veins, due to the pumping action of
blood by the heart. Arteries therefore have
thicker walls to counteract the pressure by
which blood moves through them. The
capillaries lack both the tunica externa and the
tunica interna.
In addition, the walls of the arteries are more
elastic thanthose of veins, in order to overcome
the pressure by which blood flows through
them by rapidly stretching without bursting.
Also arteries have a narrower rumen thanveins,
which increases the pressure of the blood
flowing through them.
Arteries also lack valves while veins have valves
which prevent the backflow of blood in veins.
However, arteries do not need valves since they

transport blood under high pressure, which
pressure ensures that blood flows forward.
Blood in arteries movesinform of pulseswhile in
veins is flows smoothly without any pulse. A
pulse is a series of waves of dilation that pass
alongthe arteries caused by the pressureof the
blood pumped from the heart through
contractions of the left ventricle.
Arteries transport oxygenated blood from the
heartto thetissuesexcept thepulmonaryartery
which transportsdeoxygenated blood from the
heart to the lungs while veins transport
deoxygenated blood from tissues to the heart
except the pulmonary vein which transports
oxygenated blood from the lungs to the heart.
Therefore arteries can be defined as blood
vessels which transport blood away from the
heart and veins are defined as blood vessels
which transport blood from the tissues to the
heart.
Adaptations of blood capillaries
1. Blood capillaries are the smallest blood
vesselsfound in close contact with tissuesin
form of a dense networkwhich allowsa high
rate of diffusion of materials during their
exchange between the blood circulatory
system and the tissues.
2. They are numerousin numberto provide
a large surface area which increases the rate
of diffusion and allows rapid exchange of
materialsbetween bloodandthetissuefluid.
3. They have a thin and permeable
membrane which is made up of thin
flattened pavement cells which allow rapid
diffusion and exchange of materials
between blood and tissues with minimum
resistance.
4. They possess the capillary sphincter
muscles which contract and relax so as to
regulate the amount of blood entering into
the capillary network.
5. Some capillaries have a bypass
arteriovenous shunt vessel which links the
arterioles and venules directly so as to
regulate the amount of blood which flows
through the capillary network e.g. in the
capillaries of the feet, hands, stomach e.t.c.
The capillary network offers maximum
resistanceto bloodflowing throughthemhence
decreasingthespeed of bloodflow which allows
the maximum diffusion and exchange of
materials between blood and the tissues.
Diagram showing the capillary network
THE MAMMALIAN HEART
Structure of the mammalian heart
The heart is the muscular organ pumping blood
to all body organsusing its chambers. It is made
up of four chambers which include the right and
left atria (auricles) and the right and left
ventricles. The four chambers enhance the
blood flow through the heart at the same time
without mixing it i.e. deoxygenated blood is
separated from oxygenated blood. The
oxygenated blood flows throughthe left atrium
and ventricle while the deoxygenated blood
flows through the right atrium and ventricle.

The heart is composed of the cardiac muscles
within its walls which are myogenic in nature,in
a way that, the initiation of their contraction is
not under the control of the central nervous
system but is within the muscles themselves.
This enables them to contract continuously and
rhythmically without fatigue and therefore
enables the heart to beat and pump without
stopping.
The heart consists of atrio-ventricular valves/
pocket valves and semi lunar valves. The atrio-
ventricular valves include the following;
a. The three (3) flapped tricuspid valves
foundbetween the rightatriumandthe right
ventricle
b. The two (2) flapped bicuspid valves
which prevent back flow of blood from the
left ventricle to the left ventricle.
The semi lunar valves are prevented from
turning inside out by connective tissues called
tendinous cords
The heart linked with four blood vessels which
include the following;
i. The venacava which transports
deoxygenated blood from body tissues through
the right atrium of the heart.
ii. The pulmonary artery which transports
deoxygenated blood from the right ventricle of
the heart to the lungs.
iii. The pulmonary vein which transports
oxygenated blood from the lungs into the left
atrium of the heart.
iv. The aorta which is the biggest vessel and
it transports oxygenated blood from the left
ventricle of the heart to the body tissues.
The left ventricle is more muscular(thicker)than
the right ventricle because the left ventricle has
to contract more powerfully than the right
ventricle in order to enable oxygenated blood
with high pressure to move for a long distance
to the body tissues unlike the right ventricle
which pumps deoxygenated blood with low
pressure for a short distance to the lungs.
Question:
Explain the suitability of the cardiacmuscle to its
function. (13 marks)
1. Many (large) mitochondria; to provide
energy for contraction of the muscle;
2. Actin and myosin filaments; makes the
muscle contract and relax;
3. Intercalated discs; modified to allow rapid
diffusion of ions; and hence rapid spread of
action potential through the muscle;
4. Tough junctions between myofibrils of
successive cells; hold the cells together
during contraction;
5. Branched fibres; rapid spread of excitations
through the whole muscle;
6. Longer absoluterefractory period; allow the
muscle to recover fully; during rapid
contractions; without fatigue; tetanus;, and
oxygen debts;
The significance of the difference in the
thickness of the walls of heart ventricles.
1. The right ventricle is thicker than the left
ventricle;
2. The rightventricle pumpsbloodto the lungs;
which are near the heart; thus lower
pressure is required; to prevent damage of
the lung capillaries;
3. The left ventricle pumps blood to all the
partsof thebody; some of which arefar from
the heart; and a high pressureis required; to
overcome the peripheral resistance;

How the internalstructureof theheart issuited
for its functions
 Cardiac muscle fibres interconnected to form a
network of fibre to ensure rapid and uniform
spread of excitation throughout the walls of the
heart;
 Heart divided into 4 chambers to enable
differential generation of pressure;
 Ventricles have thicker walls than auricles to
generate higher pressure to drive blood over
long
 distance into more elaborate circulation/to the
lungs and to all body tissues;
 Walls of left ventricles are thicker than those of
right ventricles to generate more pressure to
pump
 blood to longer distance in the systemic
circulation/rest of the body;
 Longitudinal septum which separates the heart
into two halves to prevent mixingof oxygenated
and deoxygenated blood;
 Valves to prevent back flow of blood;
 Valves have strands of connecting tissue
(Chordas tendinae) to prevent them from being
pushed
 inside out when ventricles contract;
 Sino Atrial Node (S.A.N) acts a pacemaker
regulating rate of beating and excitation of
heart;
 Heart located in the thoracic cavity where it is
protected from any external mechanical
damage;
 Atrio Ventricular node (A.V.N) which delays
depolarization wave from Sino Atrial Node to
ensure that auricles empty completely before
the ventricles contract;
 Purkinje tissues to relay waves from A.V.N to
ventricular myocardium;
Question: Although the heart is myogenic, it is
innervated. Explain the significance of the
innervation of the heart. (07 marks)
1. Maintains a constant heartbeat rate under
normal circumstances;
2. The AVN delays the ventricular systole until the
atria contract; which allows time for ventricles to
fill with blood before they can contract;
3. Ensures that atrial systole occurs before
ventricular systole; to pump blood from atria to
ventricles;
4. Ensures that atrial systole begins from the top of
the heart proceeding downwards; so that blood
is squeezed into the ventricles;
5. Through the bundle of His, it ensures that the
main contraction of the ventricles starts at the
bottom of the heart and spreads upwards;
squeezing blood out on the ventricles;
Initiation of the heart beat
The cardiac muscle within the walls of the heart
is myogenic in nature in a way that the initiation
of its contraction is within the muscle itself, but
not under the control of the central nervous
system (brain and spinal cord). This enables the
muscles to contract continuously and
rhythmically without fatigue to enable the heart
to beat continuously and rhythmically without
stopping. The intrinsic initiation of the heart
beat enables the heartto remain beating even it
is surgically removed from the body, provided it
is under ideal conditions.
The rhythmic contraction of the cardiac muscles
is initiated by specialized networkof fine cardiac
muscles network found inside the wall of the
right atrium close to the entrance of blood from
venacava into the right atrium. This network of
fine cardiac muscle fibre is known as Sino Atrial
Node (SAN) and it serves as a pace maker by
giving off a wave of electrical excitations similar
to impulses, which spread out very rapidly over
both atria causing them to contract and force
blood into the ventricles via the open atrial
ventricular valves.
When the electrical excitations reach the
junction at the boundaryof the atria, they excite
another specialized plexus of other cardiac
muscle chamber known as Atrio-Ventricular
Node (AVN). When excited, the AVN sends
waves of electrical excitations down to another
bundle of cardiac muscle of fibres formed along

the inter-ventricular septum called the Purkinje
tissue or Bundle of His to the apex of the heart.
This conducts and spreads the excitement to
both ventricles which eventually pump blood
into the arteries. .
Other extrinsic controls such as baroreceptor
activity, hormones like thyroxine, age, exercise
and body temperature.
Diagram showing how the waves of electrical
excitations spread from the SAN
Question: Explain how the action of the heart is
controlled (08 marks)
Approach;
 Intrinsically by a set of specialized cardiac
cells which initiate and distribute electrical
signals myogenically throughout the heart;
The SANas thepacemaker; spreadselectrical
excitations to atria; making them contract;
excitation wave thenreachesthe AVN;which
delays and relays signals through purkinje
tissue; and the bundle of His; to the
ventricles; which then contract.
 Extrinsically by the autonomic nervous
system; Sympathetic nervous system
releases noradrenaline; facilitates
depolarization of cardiac muscles; increases
cardiac activity; Parasympathetic nervous
system (vagusnerve);releasesacetylcholine;
hyperpolarizes cardiac tissue; decrease
cardiac activity;
 Other extrinsic controls such as
baroreceptor activity, hormones like
thyroxine, age, exercise and body
temperature.
NB:
Duringexercises thatrequire muscularwork,the
body muscles contract strongly and this
increases the rate of venous blood returning to
the heart. The walls of the vena cava are
stretched by large quantities of blood and
therefore this increases heart rate.
Hormonal control of heart rate
Two hormones are known to play an important
role in the heart rate. These include adrenaline
secreted by the adrenal glands and thyroxine
secreted by the thyroid glands.
Adrenaline hormone is secreted when a person
is experiencing a surprise, shock, fear or
excitement. It has the effects similar to that of
the sympathetic nervous system of increasing
the heart rate in the following ways;
a) Directly by stimulating the SAN to
increase the frequency of which it emits waves
of depolarization which bring about
contractions of the atria.
b) Indirectly by increasing the metabolic
rate.
Thyroxine increases the heart rate in the following
ways;
a) Directly by stimulating the SAN to increase
the frequency it which it emits waves of
excitation.
b) Indirectly by increasing the basal metabolic
rate whichraises oxygenconsumption bythe

respiring tissues, hence increasing the
oxygen demand and supply to the tissues.
Other factors that affect heart rate
a. Bradycardia and tachycardia
Bradycardia refers to the reduction of heart shown
by slow pulse rate of less than 70 beats per minute.
This is due underactivity of the thyroid gland
(hypothyroidism) and also changes in the electrical
activity of the cardiac muscles.
Tachycardia refers to the rapid beating of the heart
due to over activity of the thyroid gland
(hyperthyroidism). It is also due to changes in the
activity cardiac muscles.
b. Temperature; low temperature reduces
heart rate amd high temperature increases
heart rate.
c. Carbon dioxide concentration; high carbon
dioxide concentration in blood increases
heart rate and the reverse is also true.
d. Some mineral ions affect heart rate e.g
calcium and potassium ions.
e. The state of health of an individual; some
diseases like malaria affects heart beat rate.
f. Psychological status of the person.
g. Age
Question : Describe the role of the medulla in the
control of heartbeat rate. (11 marks)
Approach
 During a vigorous physical activity much blood
returning to the heart stretches the vena cava;
impulses are conveyedfrom the venacava to the
cardiac accelerator centre in the medulla; which
responds by sending impulses via the
sympathetic nerve; to the SAN; and the
heartbeat rate is increased;
 The heart responds by contracting more strongly
and much blood is forced out of the heart;
 As much blood leaves the heart the aorta and
carotid arteries are stretched; which stimulates
the stretch receptors that send the impulses to
the cardiac inhibitory centre in the medulla; that
respond by sending impulses to the SAN; and
AVN; via the vagus nerve; to inhibit further
contraction; and the heart rate is reduced
Cardiac cycle
Rhythmic contraction and relaxation of the
cardiac chambers i.e. the auricles and the
ventricles in a specific manner during one heart
beat constitutesa cardiac cycle. The heart beats
continuously without pause in life. Auricles and
ventricles show rhythmic contractions and
relaxations.On average heartbeats 72 times per
minute. Heart pumps about 5 litres of blood per
minute. Both auricles contract simultaneously
and the blood flows into the ventricles and both
ventricles contract together forcing the blood
into pulmonary artery and aorta.
Systole: Refers to the contraction of the cardiac
chambers and as a result the heart contracts
forcing the blood into the pulmonary artery and
the aorta.
Diastole: This refers to the relaxation of the
cardiac chambers hence enabling the heart to
refill.
Joint diastole: This refers to the relaxed state of
both atria and ventricles.
Sequence of changes in cardiac chambers
during one cardiac cycle
Atrial filling and joint diastole:
Filling of right atrium (RA) with deoxygenated
blood from the great veins and left atrium (LA)
with oxygenated blood from pulmonary vein.
As the pressure increases in the atria, the
bicuspid and tricuspid valves open and blood
flows into the respective relaxed ventricles.
The semilunar valves remain closed because of
the low pressureand blooddoes not flow out of
the ventricles.
Atrial systole and ventricular diastole:
At the end of joint diastole, next heart beat
begins. The two atria contract, forcing most of
the blood into the ventricles.
Simultaneous closing of great vein roots
(superiorandinferior venacava)by compression
occurs. Bicuspid and tricuspid valves are open.
Ventricular systole (VS) and atrial diastole(AD):
Ventricles contract while atria relax. This forces
the atrio ventricular valves to close producing
thefirst heartsound‘lub’.This preventstheback
flow of blood into the auricles. As the chambers

contract, then the ventricular pressure exceeds
the pressure in the pulmonary artery and aorta
forcing the opening of the semi lunar valves.
Blood flows from ventricles to great arteries. It
lasts for about 0.25 seconds.
Ventricular diastole and atrial diastole
(beginning of joint diastole):
Ventriclesrelax andthepressurefallsbelow that
in the great arteries. This causes the closing of
the semilunarvalvesinthe pulmonaryarteryand
aorta to produce the second heart sound ‘dub’.
This prevents backflow of blood into ventricles.
As the low ventricular pressure is still greater
than the atrial pressure, the AV valves remain
closed.
Continued ventricular diastole decreases the
pressure tremendously and now both atria and
ventricles are in joint diastole. This lasts for
about 0.4 seconds.
One complete systole and diastole (described
above) forms a cardiac cycle which takes about
0.8 seconds. The new cardiac cycle begins with
the atrial systole.
Question
(a) Describe the events of the cardiac
cycle.
Approach
The right and left ventricles relax simultaneously
(ventricular diastole) while the right and left atria
contract (atrial systole); pressure in atria increases
above that of ventricles; the tricuspid and bicuspid
valves (atrio-ventricular valves) are open; blood flows
into ventricles from the atria; and contraction of the
atrial wall alsohasaneffect ofsealing offthevenacava
and pulmonary vein, preventing back-flow of blood
into the veins as the blood pressure in the atria rises;
right and left ventricles contract simultaneously
(ventricular systole) and the right and left atria relax
(atrial diastole); thesemilunar valves are forced open;
blood is pumped from the ventricles into the
pulmonary artery and aorta; tricuspid valves and
bicuspid valves are closed; due to theslight backward
movement of bloodasaresult oftheraisedventricular

pressure; thefirst heart sound(lub) is produced;after
ventricular systole there is a short period of
simultaneous atrial and ventricular relaxation
(diastole); ventricular pressure decreases below that
ofblood inarteries; bloodflowsback against thecusps
of semilunar valves forcing them closed; 2nd
heart
sound(Dub) produced; Blood then flows from the
veins through the relaxed atria into the ventricles;
whichfill passivelyandthecyclecontinues @
1mark max = 12 marks
OR
Atrial systole:
Both atria contract; small amount of remaining
blood forced into the relaxedventriclesviatheopen
AV valves;
Ventricular systole;
Both ventricles contract; The atrioventricular
valvesarepushedshut bythe pressurizedbloodin
the ventricles; Heart sound I (lub) produced;
Ventricular pressure being greater than arterial
pressure forces semilunar valves open; Blood
ejected from the ventricles into the arteries;
Atrial and ventricular diastole;
Ventricles and atria relax; ventricular pressure
drops; blood flows back against the cusps of
semilunar valves; forcing them closed; 2nd heart
veinsthrough therelaxedatriaintothe ventricles;
which fill passively and the cycle continues
Q.1 Describe the patterns of; (i) atrial pressure
(ii) ventricular pressure
(a) (i) Pattern of atrial pressure
Initially at 0 second atrial pressure is low;
Increases gradually from 0 second to a peak at
0.08 seconds; Decreases gradually from 0.08
secondsto0.14 seconds;Increases verygradually
from 0.14 seconds to a peak at 0.16 seconds;
Decreases rapidly from 0.16 seconds to 0.19
seconds; Increases gradually from 0.19 seconds
to a peak at 0.4 seconds; Decreases rapidly from
0.4 seconds to 0.44 seconds; Increases very
gradually
from 0.44 seconds to a peak at 0.58 seconds;
decreases very gradually from 0.58 seconds to
0.6 seconds;
(ii) Changes in ventricular pressure
Initially at 0 second ventricular pressure is low;
increases gradually from 0 seconds to a peak at
0.08 seconds; Decreases very gradually from
0.08 seconds to 0.14 seconds;
Increases very rapidly from 0.14 seconds to 0.16
seconds;increases rapidly from 0.16 secondsto a
peak at 0.28 seconds; Decreases gradually from
0.28 seconds to 0.38 seconds; Decreases very
rapidly from 0.38 seconds to 0.42 seconds;
increases very gradually from 0.42 seconds to a
peat at 0.58 seconds; Decreases very gradually
from 0.58 seconds to 0.6 seconds;
(b) Differences in changes in ventricular
pressure and ventricular volume
From 0.14 seconds to 0.16 seconds ventricular
pressureincreases very rapidly, while ventricular
volume increases very gradually;
pressure increases, while ventricular volume
decreases;
pressure decreases, while ventricular volume
increases;
pressure increases very gradually, while
ventricular volume increases very rapidly;
Ventricular pressure attains a peak later at 0.28
seconds, while ventricularvolume attains a peak
earlier at 0.16 seconds;
1. (c) Effect of changes in atrial, aortic and
ventricular pressures
From 0 second to 0.14 seconds represents atrial
systole; when atrial cardiac muscle contracts; to
decrease atrial volume and increase atrial

pressure above ventricular pressure; forcing
bloodflow from the leftatrium throughtheopen
bicuspid value; into the relaxed left ventricular;
From 0.14 seconds to 0.38 seconds represents
ventricular systole; There is more powerful
contraction of left ventricular cardiac muscle
than the atrial cardiac muscle; which decreases
ventricular volume while increasing ventricular
pressureabove atrialpressure;forcing closureof
bicuspid valve to prevent backflow of blood into
the left atrium; Ventricular pressure increases
furtherexceeding aortic pressureat0.16seconds
to force open semilunar/aortic valves; hence
allowing left ventricular blood flow into aorta;
From 0.38 seconds to 0.6 seconds represents
diastole; The left ventricular cardiac muscle
relaxes to increase ventricular volume and
decrease ventricular pressure below aortic
pressure; forcing closure of semilunar / aortic
valve to prevent backflow of blood; At 0.4
seconds ventricular pressure decreases further
below atrial pressure to force opening of
bicuspid valve; and flow of oxygenated blood
from the left atrium into the left ventricle;
1. (d) (i) Pattern of electrical activity
P wave corresponds to the wave of electrical
excitation spreading over the atria during atrial
systole/contraction;
QRS wave corresponds to the wave of electrical
excitation spreading over the ventricles during
ventricular systole/contraction;
T wave corresponds to the wave of electrical
excitation spreading over the ventricles during
ventricular diastole/relaxation;
(ii) Pattern of Sounds on the phonocardiogram
1 is the first heart sound produced by the sudden
closure of the atrioventricular valves; [described
as the ‘lub’]
2 is the second heart sound produced by the
sudden closure of the semilunar valves of the
aorta and pulmonary artery; [described as the
‘dub’]
(e) Explain how the internal heart structure is
related to its functioning
- Cardiac muscle fibres interconnected to form a
network of fibre to ensure rapid and uniform
spread of excitation throughout the walls of the
heart;
- Heart divided into 4 chambers to enable
differential generation of pressure;
- Ventricles have thicker walls than auricles to
generatehigher pressuretodrive bloodover long
distance into more elaborate circulation/to the
lungs and to all body tissues;
- Walls of left ventricles are thicker than those of
right ventricles to generate more pressure to
pump
blood to longer distance in the systemic
circulation/rest of the body;
- Longitudinal septum which separates the heart
into two halves to prevent mixing of oxygenated
and deoxygenated blood;
- Valves to prevent back flow of blood;
- Valves have strands of connecting tissue
(chordas tendinae) to prevent them from being
pushed
inside out when ventricles contract;
- Sino Atrial Node (S.A.N) acts a pacemaker
regulatingrate of beating and excitation of heart;
- Heart located in the thoracic cavity where it is
protected from any external mechanical damage;
- Atrio Ventricular node (A.V.N) which delays
depolarization wave from Sino Atrial Node to
ensure thatauricles empty completely before the
ventricles contract;
- Purkinje tissues to relay waves from A.V.N to
ventricular myocardium;

EXAMINATION QUESTION 2
2 (a) Describe the events of the cardiac
cycle.
The right and left ventricles relax simultaneously
(ventriculardiastole)whilethe right and leftatria
contract (atrial systole); pressure in atria
increases above that of ventricles; the tricuspid
and bicuspid valves (atrio-ventricular valves) are
open; blood flows into ventricles from the atria;
andcontraction of the atrialwallalsohasan effect
of sealing off the vena cava and pulmonary vein,
preventing back-flow of blood into the veins as
the blood pressurein the atriarises; right and left
ventricles contract simultaneously (ventricular
systole) and the right and left atria relax (atrial
diastole); the semilunar valves are forced open;
blood is pumped from the ventricles into the
pulmonary artery and aorta; tricuspid valves and
bicuspid valves are closed; due to the slight
backward movement of blood as a result of the
raised ventricular pressure; the first heart sound
(lub)is produced;afterventricularsystole thereis
a short period of simultaneous atrial and
ventricular relaxation (diastole); ventricular
pressure decreases below that of blood in
arteries; blood flows back against the cusps of
semilunar valves forcing them closed; 2nd heart
veinsthrough therelaxedatriaintothe ventricles;
which fill passively and the cycle continues
@ 1mark max = 12 marks
(b) Explain how the heart action is
controlled.
Control of heart action can be nervous;
hormonal; by changes in pH; by changes in
temperature;
In nervous control, stretching of aorta due to
increase in stroke volume; stimulates the
release of impulses from stretch receptors in
the aorta and carotids; these are sent to the
cardiac inhibitory centre; in the medulla of the
brain; in turn sending impulses via the vagus
nerves; to the sino-Atrial node (SAN) and
Atrio-ventricular Node (AVN); decreasing the
heart rate; while those from stretch receptors
in the vena cava are sent to the cardiac
accelerator centre in the medulla of the brain;
which in turn sends impulses sympathetic
nerves; to the SAN and AVN; increasing the
heart rate;
Action of hormones Adrenaline from adrenal
glands; and thyroxin from thyroid glands;
once secreted into the blood stream; these
increase the metabolic activity; increasing the
heart action to meet the oxygen demand;
Accumulation of carbon dioxide in blood
during exercise; lowers blood pH; increasing
heart rate; while high pH decelerates heart
action;
@ 1mark max = 08 marks
CONTROL OF BLOOD PRESSURE
Blood pressure is the force developed when a high
volume of blood pushes against the walls of blood
vessels. There are two types of blood pressure,
namely;
 Diastolic pressure
 Systolic pressure
Diastolic blood pressure
This is the blood pressure developed in the arteries
when the ventricular cardiac muscle of the heart
relaxes, resulting in the expansion of the ventricles
to fill with blood. It is always lower than systolic
pressure and it is 80mmHg
Systolic blood pressure
This is the pressure developed in the arteries at the
contraction of the ventricular cardiac muscle of the
heart, resulting in the pumping of blood out of the
heart. It is always higher than diastolic blood
pressure and it is 120mmHg.
Cause of blood pressure
1) Heart rate

2) Cardiac output
3) Peripheral resistance towards blood flow
by arteries.
4) The strength of the heartbeat
Maintenance flow of blood in humans.
1.Arteries; receive blood from the heart
under high pressure; during ventricular
systole; This pressure moves the blood in
the arteries throughout the body; The
movement is pulsative at first; flowing
fast at systole and slow at diastole; but
further away from the heart, blood flows
evenly; due to elastic recoil of the
smooth muscles in the arteries;
2. Veins; blood flow is due to the
action of the skeletal muscles
squeezing them; and back flow is
prevented by the valves present
along their walls;
The large diameter minimizes
resistance to blood flow;
The negative pressure developed in
the thorax during inspiration draws
back blood towards to the hearts;
An illustration of the factors regulating
blood pressure, heartbeat and breathing
rate.
Control of blood pressure
When blood pressure increases beyond
normal, the baroreceptors of the carotid
artery and aortic arch are stimulated.
Impulses are fired via afferent nerves or
sensory neurone to the vasomotor centre of
the medulla oblongata.
These centrefire impulsesalongthevagusnerve
of the parasympatheticsystemto theSAN which
responds in turn by firing waves of excitation
less fat than usual/sympathetic output is
suppress. The heart beat reduces and cardiac
output reduces. The blood pressure is reduced
to normal.
The impulses from the vasomotor center
sent through the vagus nerve to arterioles
cause vasodilation of arterioles. This reduces
peripheral resistance towards blood flow,
hence blood pressure reduces to norm.
When the blood pressure lowers below the
norm, the baroreceptors fire impulses via
afferent nerves to the vasomotor center of
the medulla oblongata of the brain. The
vasomotor centre responds by firing
impulses to the SAN along sympathetic
nerve. These impulses stimulate the SAN to
increase the frequency at which it sends
waves of excitation to increase heartbeat,
cardiac output and pressure/sympathetic
output increases.
Some impulses from the vasomotor center
sent via the vagus nerve are send to the
blood arterioles where they stimulate vaso-
constriction of arterioles. This
enhances/increases peripheral resistance to
blood flow, which increases the blood
pressure.

The significance of controlling blood
pressure.
1. Adequate blood pressure is required to
move blood from the heart through the
arteries; to the capillaries; and then move
it back to the heart in the veins;
2. Low blood pressure would affect the
delivery of materials to the tissues; and
the speed of blood returning in the veins;
3. High blood pressure would lead to
bursting of delicate capillaries;
haemorrhages; and heart infarction;
affecting vital body organs which may be
fatal;
Qn: Explain the effect of increased levels of
carbon dioxide in blood on blood pressure in
man. (07 marks)
 Increased amount of carbon dioxide is
detected by the chemoreptors in the
carotid and aortic bodies; the send
impulses through the afferent neurones
to vasomotor centre;
 The vasomotor centre sends impulses to
blood vessels (arterioles) via the
sympathetic nerves; which causes them
to constrict; and blood pressure
increases;
 Carbon dioxide also directly stimulates
the blood vessels in the area where it
produced to dilate; so that more blood
flows in this region;
 Increased carbon dioxide levels also
stimulates the cardiac accelerator centre
that sends impulses to the SAN via the
sympathetic nerve to increase the cardiac
output; and hence blood pressure
increases
A diagram showing the location of
baroreceptors
Factors responsible for enhancing blood
pressure.
 Pumpingaction of theheart which forces
blood at high pressure in one direction
through the arteries.
 Narrow lumenof arteries which maintain
high pressure of forward flow of blood.
 Aortic valves at the base of the aorta
close andpreventback flow of bloodinto
the heart.

 Atrio-ventricular valves within the heart
prevent blood back flow to ensure
forward flow of blood from the heart.
 Valves in veins push blood forwards to
prevent back flow.
 Wider lumenin veins reduceresistanceto
blood flow such that unidirectional flow
is maintained.
 Inhalation causes sunction pressure that
pulls blood in veins towards the heart.
 Muscular contraction, especially skeletal
muscles exert force onto veins, which
squeeze the veins and causes flow
towards the heart.
 Effect of hydrostatic pressure at the end
of the capillary bed.
 Effect of gravity pulls blood in blood in
veins head back to the heart
 Residual heart pressure.
Pressure changes in the circulatory system
The pressure of the blood changes as it moves
through the circulatory system. The changes are
illustrated in the graph below:
Observation and explanation:
1. In the arteries, blood is at high pressure
because it has just been pumped out of the
heart. The pressure oscillates (goes up and
down) in time with the heartbeat. The
stretching and recoil of the artery walls helps
to smooth the oscillations, so the pressure
becomes gradually steadier the further the
blood moves along the arteries. The mean
pressure also gradually decreases,
particularly as the blood flows through
arterioles (small arteries).
2. The total cross-sectional area of the
capillaries is greater than that of the arteries
that supply them, so blood pressure is less
inside the capillaries than inside arteries.
3. In the veins, blood is at a very low pressure,
as it is now a long way from the pumping
effect of the heart.
CIRCULATION IN MAMMALIAN FAETUS
the mammalian fetus obtains its oxygen and
nutrients from the placenta in the mother`s
uterus. The placenta also removes wastes from
the fetal blood. The placenta also removes
wastes from the fetal blood. Maternal blood
vessels come into close contact to one another
in the placenta. The functions of the fetal lungs,
kidney and gut are performed by the placenta.
At birth, several changes take place to blood
circulation.
Changes that occur in blood and faetal
circulation at birth.
BEFORE BIRTH
-Foetal haemoglobin has a higher affinity for
oxygen than adult haemoglobin to facilitate
diffusion of oxygen from the mother.
- In the foetus, blood bypasses the lungs via
the ductus arteriosus, which connects the
pulmonary artery to the aorta.
- Blood also bypasses the lungs, which are
functionless by going through the foramen
ovale connecting the two atria of the foetal
heart.This resultsinthe mixing of oxygenated
blood from the placenta and deoxygenated
from the foetal tissues in the posterior vena
cava and in the heart.
-Blood from theleft atriumpassesinto the left
ventricle and into the aorta, which supplies

blood to the body and the umbilical artery.
Pressure in the foetal circulatory system is
greatest in the pulmonary artery and this
determines the direction of blood flow
through the foetus and placenta.
AFTER BIRTH
-In a few weeks of life, foetal haemoglobin is
replaced by adult haemoglobin since it is less
suitable as a means of gaseous exchange with
air.
-At birth when the baby takes the first breath,
there is increased partial pressure of oxygen in
its blood together with the nervous reflexes
occurring in its body results in the closure of
ductus arteriosus.
-As aresultof this, most of the bloodvesselsand
the opening of pulmonary circulation results in
the blood pressure in the left atrium exceeding
that of the right atrium, causing the foramen
ovale to close with the aid of a valve in its
passage.
-Blood then passes from the right ventricle and
pulmonary artery to the lungs.
Note: sometimes the mechanism which results in
the closure of foramen ovale fails. This is the
reason why some children called blue babies bear
a hole in the heart, where a portion of blood
continues to bypass the lungs resulting in
inadequate oxygenation of the tissues.
What major change would occur in the foetal
circulation if blood pressure were highest in the
aorta?
Blood would flow in the reverse direction along the
ductus arteriosus.
Illustration of the blood circulation in mammalian
foetus.
BLOOD GROUPS AND BLOOD TRANSFUSION
There are basically two blood group systems;
ABO system and the Rhesusfactor system. Both
systems have to be considered during blood
transfusion
ABO system
Under this system, there are four blood groups:
a) Blood group A
b) Blood Group B
c) Blood Group AB
d) Blood Group O
A person’s type of blood is determined by
carbohydrate or protein structures located on
the extracellular surface of the Redblood cell
membrane.These structuresarecalled antigens.
So if a person is of;
i. Blood group A, he or she has the A type
antigens
ii. Blood group B, he or she has the B type
antigens
iii. Blood group AB, he or she has the A and
B types of antigens

iv. Blood group O, he or she lacks antigens
on his or her red blood cells.
The antigens of an individual’s red blood cells
have corresponding antibodies in the plasma of
blood which are different from the antigens in
that;
a) A person of blood group A has antibodies of
type b.
b) A person of blood group B, has antibodiesof
type a.
c) Apersonof bloodgroupAB, hasnoantibodies
to any ABO blood group antigens.
d) A person of blood group O has antibodies of
type b and a.
During blood transfusion, the blood of the
recipient should not have antibodies against
antigens of blood donated by the donor
otherwise agglutination will occur.
NB: Blood transfusion is the blood transfer
process from the donor to the receiver.
Agglutination is the formation of a blood clot
due to a reaction between the antigens in the
donor’s blood and antibodies in the recipient’s
blood.
Question: Explain what would happen if an
individual of blood group A is transfused with
blood of;
(i) Blood group B. (06 marks)
® Agglutination of the donor red blood cells
occurs; because the donor red blood cells
have antigenB; while the recipient bloodhas
antibodies b due to presence of the antigen
A;
® Upon receiving the blood, the antibodies in
the recipient interact with the antigens on
thered bloodcellsof thedonormakingthem
to clamp together;
® The clamped up cells can cause blockage of
narrowbloodvessels;leadingtodeathof the
recipient;
® The antibodies a present in the donor blood
do not have serious impacts; because they
arein very few amountsthuseasilydilutedby
the recipients’ blood;
(ii) Blood group O (04 marks)
When transfused into an individual of blood
group B no agglutination occurs; because blood
of blood group O contains no antigens;
The antibodies a and b; present in the donor
blooddo nothaveserious impacts; becausethey
are in very few amounts thus easily diluted by
the recipients blood;
DEFENCE AGAINST DISEASES
Every mammal is equipped with a complex
system of defensive mechanisms which are
designed to enable it prevent the entry of
microbes into it, to withstand attacks by
pathogens (disease causing micro-organisms)
and to remove foreign materials from the
system.
The defensive mechanismsof bloodinclude
the following;
a. Clotting of blood
b. Phagocytosis
c. Immune response to infection
Clotting of blood
When a tissue is wounded, blood flows from it and
eventually coagulates to form a blood clot which
covers the entire wound. This prevents further blood
loss and entry of pathogens. The process of blood
clotting is described below.
When blood platelets and damaged tissues are
exposedto air, the platelets disintegrate and release
an enzyme calledthromboplastin or thrombokinase,
which in the presence of plasma proteins, clotting
factors (VIII) and calcium ions catalyzes the
conversion of a plasma protein derived from vitamin
K called Prothrombin into thrombin enzymes.

Thrombin is a proteolytic enzyme that hydrolyses a
plasma protein called fibrinogen into an insoluble
protein called fibrin. Fibrin forms fibres at the
wounded area. Within the fibrous network of fibrin
blood cells become trapped, therebyforming a fibrin
clot or a blood clot.
The clotnot only preventsfurtherblood loss, butalso
prevents the entry of bacteria and other microbes
which might otherwise cause infection.
Note:
Heparin is an anticoagulant which inhibits the
conversion of prothrombin to thrombin thereby
preventing blood clotting.
Apart from blood clotting, the entry of microbes into
the body can be prevented by the following;
i) Using impermeable skin and its protective
fluid called sebum (oily secretion in the skin)
ii) Using mucus and cilia to trap the microbes
and then remove them
iii) By using hydrochloric acid in the stomach
iv) By using lysozyme enzyme in the tears and
nasal fluids
v) By vomiting and sneezing
Why blood does not clot in the vessels
1. Connective tissue plus the liver produce
chemical, heparin, which prevents the conversion of
prothrombin to thrombin, and fibrinogen to fibrin.
2. Blood vessels are smooth to the flow of
blood. Damage to the vessel’s endothelium can lead
to platelets breakdown which leads to clotting of
blood.
WOUND HEALING
 Towards the end of inflammation, fibroblasts
start secreting collagen. Collagen has a
secondary protein structure.
 Collagen’s secondary structure enables it to
link to polysaccharides forming a scar in
presence of vitamin C.
 Vitamin C attaches hydroxyl groups of
polysaccharides to collagen fibres.
 Fibres in scar tissue get reorganized into
bundles arranged inline of stress of the wound.
 Blood vessels begin to spread through the
wound supplying nutrient for repair.
 Epidermal cells migrate to the surface and
ingestmuch of the debris andfibrinin the clots.
When they unite to form a continuous layer
under the skin.
 Later, the scab sloughs off.
Phagocytosis
This is mainly carried out by neutrophils and
macrophages obtained from Monocytes. These are
amoeboid cells attracted to areas where cell and
tissue damage has occurred.The neutrophilsare able
to recognize any invading bacterial cells. This
capability of neutrophils is enhanced by plasma
proteins called opsonins which become attached to
the surface of the bacteria and in some way make
them easily recognize by the neutrophils. The
neutrophils bind to the bacteria so as to carryout
Phagocytosis.
After binding themselves to the bacteria, the
bacteria are engulfed in an amoeboid fashion and
then a phagosome is formed. Small lysosomes called
primary lysosomes within the neutrophils fuse with
the phagosome to form a phagolysosome.
Hydrolytic enzymes are then poured into the
phagolysosomes from which the lysosomes and the
bacteria are digested. The soluble materials of
bacterial secretion are then absorbed in the
surrounding cytoplasm of neutrophils.
Neutrophils are able to squeeze themselves through
the walls of blood capillaries, a process called
diapedesis and move about in the tissue spaces.
In organs such as the liver, spleen and lymph nodes
are large resistant phagocytic monocytes known as
macrophages. The macrophages together with the
neutrophils form the body’s reticulo-endothelial
system that defects the body against diseases.
Diagrams showing the process of Phagocytosis of
a bacterium by a neutrophil

Immune response to infection
Immunity is the capacity of an organism to
recognize the entry of materials foreign to
the body and mobilize cells and cell
products to remove suchforeign materials
with greater speed and effectiveness.
Immunity involves recognition of the
foreign material (antigen) and production
of chemicalswhich destroy it (antibodies).
An antibody is a protein synthesized by
plasma cells derived from lymphocytes in
response to the presence of the foreign
substance called antigenfor which it has a
high affinity. Antigens are foreign
materials such as pathogens, toxins and
foreign blood cells to the body which
stimulate antibody formation to fight
them. When antigens gain entry into the
body, they stimulate the production of
antibodies which react with antigens and
destroy them or inactivate them.
Antibodies are formed in response to
specificantigens andare namedaccording
to the type of their activity as follows;
a) Opsonins
These are antibodies which get
attached onto the surface of the
pathogens to enable phagocytic
leucocytes such as neutrophils to
recognize the pathogens, then engulf
and destroy them.
Opsonisation is the coating of bacteria with
proteins called opsonins so that they can be
easily destroyed by phagocytic enzymes.
b) Agglutinins
These are antibodies which cause foreign cells
in the specific antigen to clamp together
making them more vulnerable to attack from
other types of antibodies. The process is called
agglutination.
c) Lysins
These are antibodies which attach themselves
on the antigens (foreign bodies) causing such
antigens to burst and rapture in smaller pieces.
The process is called lysis.
d) Antitoxins
These are antibodies produced in response to
particular bacterial toxins to which they bind
and neutralize their harmful effect. The
process is called neutralization.
e) Precipitin
This is antibody which combines with its
specific soluble antigen to form a precipitate
which is more easily ingested by phagocytes.
This process is called precipitation i.e. a
process in which precipitin antibodies binds
together soluble antigens into larger units
which are easily ingested by the phagocytes.
The production of antibodies in response to specific
antigens is called immune response.
B and T-Lymphocytes
Lymphocytesare stimulated by antigens to produce
an immune response. There are two types of
lymphocytes, B and T, which produce antibodies
directly or indirectly. The B-cells originate in the
bone marrow from the stem cells. T-cells are so
called because they are formed by a process in the
thymus gland before entering the lymph nodes by
osmosis. Inside the lymphnodes,the T-lymphocytes
do not produce antibodies but in case of aparticular
antigen entering the lymph nodes, these divide by

mitosis and give rise to different types of T-cells
which include the following;
Killer T-cells
These are cells which attach to invading cells and
secrete a number of cellular toxic substances called
lymphokines which kill the invading cells called
microbes.
Helper T-cells
These are cellsthat recognize aspecificantigenon an
antigen-presentingcell, binds to it, and then assists a
B-cell binding the same antigen to proliferate into
specific antibody secreting cells.
Suppressor T-cells
These suppress the activity of the killer T-cellsand B-
cells after the microbes have beencleared out of the
body to prevent these cells from attacking and
destroying the body cells. Suppressor T-cells
therefore regulate the immune response and
prevents antibodies from being produced by the B-
cells.
Memory B-Cells
In the presence of microbes, the receptors on the
surface of B-lymphocytes membranes, detect the
microbes and become stimulated to undergo rapid
proliferation to form memory B-cells and plasma
cells.
The memory B-cells have the ability to identify the
microbe on reinfection and then stimulate a rapid
immune response in terms of antibody production
such that the microbes are cleared out of the body
rapidly before they cause a damage which is
significant.
Antigens:
Molecules that stimulates an immune response.
Usually proteins (polysaccharides, nucleic acid,
lipids can also act as antigens) and other
inorganic molecules important for self-
recognition.
Self-antigen: Only found on the host'sown cells
anddoes nottriggeranimmune response.There
is only 1:4 change that siblings will possess an
identical antigen.
Non-self-antigen: Found on cells entering the
body (e.g. bacteria, viruses, and another
person's cell) and can cause an immune
response.
ANTIBODY/IMMUNOGLOBULIN
® An antibody is a protein molecule produced
by the body of an animal in response to a
particular antigen for which it has a high
affinity.
® An antibody is a protein molecule called
immunoglobulin (IG) composed of four
polypeptide chains linked together by disulphide
bonds.
® Two chains are long and slightly bent at the
hinge and are referred to as the heavy chains
while the twoother polypeptide chains are short
poly polypeptide chains.
® Each polypeptide chain is composed of a
constant and a variable region whereby the
constant region is the one composed of the
same amino acid sequence in all different
molecules of antibodies while at the variable
region, the amino acid sequence varies with
different molecules of antibodies.
® At one end, the two linked heavy and light chains
is an antigen binding site where a specific
antigen becomes attached. Its structure is
shown in the diagram below.
Question: Describe the following methods of antibody
function.
i. Opsonisation
• Antibodies from plasma cells begin coating pathogens at
the infection site.
• Pathogens that are tagged with antibodies are readily
destroyed by phagocytes.
ii. Complement activation
• Antibodies that are bound to pathogens also stimulate a
lethal group of proteins called the complement system.

• Complement proteins circulate in the bloodstream and
assemble at antigen– antibody complexes.
• When complement proteins activate, they punch deadly
holes in the plasma membranes of pathogens causing
bursting of the antigen carrying organism
iii. Neutralization
• Coated pathogens are blocked from interacting with—
and thus infecting—host cells.
• Their participation in the infection is neutralized.
Types of Immune Response
The immune system defends the body in the
following ways:
Non-specific way
This works by attacking anything foreign. It involves:
1. First line of defense: this is a barrier that helps
prevent pathogens from entering the body. The
body has several different types of barriers:
Tears = wash germs away, kill germs
Skin = Germs can only enter skin when you have a
cut, burn or Scrape.
Mucous Membranes = in your nose, mouth, and
throat secrete a fluid called mucus that traps germs.
Saliva = washes germs from your teeth and helps
keep your mouth clean.
Gastric juice = destroys germs that enter through
food or drink.
2. Secondline of defense: microbes that get into the
body encounter the second line of non-specific
defense.It is meant to limit the spread of invaders in
advance of specific immune responses. There are 3
types:
i) Inflammatory response: works in two ways;
 Histamine triggers vasodilation which increase
blood supply to that area, bringing more
phagocytes to engulf germs. Histamine is also
responsible for the symptoms of the common
cold, sneezing, coughing, redness and itching
and runny nose and eyes - all attempt to rid the
body of invaders.
 Increased body temperature speeds up the
immune system and makes it more difficult for
microbes to function.
Inflammation:
This is a localized reaction which occurs at the site
where a wound has been formed. It causes swelling
and a lot of pain.
The site appears red due to increased blood flow.
Capillary network dilate and become more permeable
to lymph and release lymphocytes. Chemical
substances called histamines are released to bind the
pathogens (agglutination) for easy recognition by
lymphocytes. Fibrinogen also present to assist blood
clotting if necessary.
The importance of inflammation.
1) There is release of chemical like histamine from
the damaged tissues; which cause local
vasodilation of capillaries; increasing the amount
of blood flowing in the area; and rises the
temperature locally;
2) Permeability of the capillaries also increases;
permitting the escape of plasma; containing
chemical like interferon; which make body cells
resistant to infection by viruses; and fibrinogen;
to bring about blood clotting;
3) Allows white blood cells into the surrounding
tissues; which combats the spread of the
infection;
4) Excesstissue fluid dilutes; and reducesthe effect
of potential toxic substances in the area of the
wound;
Question: outline the events that take place during
an inflammatory reaction (05 marks)
Approach:
This is a condition of pain and swelling of an infected
or wounded area due to escape of histamines and 5-
hydroxytryptamine from the damaged tissue.
 Tissue damage causes local dilation of capillaries
and raises the temperature. This increases the
temperature locally.
 Dilation also increases the leakiness of capillaries,
permitting escape of plasmaand white blood cells
into the surrounding tissues.
 Thereis subsequent swelling ofthe area -oedema.
 Plasma containschemicals like interferon secreted
by phagocytes. This increases resistance to
pathogen attack.
 Fibrinogen present assists in clotting if necessary.
 Phagocytes destroy the pathogens at the site of
infection
iii) Interferon: chemicals released by the
immune system to block against viral
infections.
Specific immune response
Lymphocytes undergo maturating before birth,
producing different types of lymphocytes

i) Humoral response - B lymphocytes
o Produce and release antibodies into
blood plasma
o Produce antibodies from B plasma cells
o Recognize foreign antigen directly.
ii) Cellular response - T lymphocytes
 Bind to antigencarrying cells and destroy
them and/or activate the humoral
response.
 Recognize foreign antigens displayed on
the surface of normal body cells
 They promote inflammation
 They stimulate B cells to make
antibodies.
iii) Primary response produces memory cells
which remain in the circulation.
iv) Secondary response new invasion by same
antigen at a lower state. Immediate
recognition and distraction by memorycells -
faster and larger response usually prevents
harm.
B-Lymphocytes: The Humoral Response
Response for pathogens not entering our cells i.e.
antibodies defend against infection in body fluids.
(E.g. bacterium).
Each B-lymphocyte recognizes only one specific
antigen or need T-helper cell to be activated.
Mature B-cells develop to give many different
variants of specific immune system responding to
any type of pathogen entering the body.
Primary response:
Pathogen is ingested by macrophages / macrophage
displays the pathogens surface non-self-antigen on
its surface (antigen presentation). It then joins with
specific T-helper cells and B lymphocytes that have
membrane receptors and are complementary in
shape to the non-self-antigen. T-helper cells will
release cytokines to activate selected
B-cell/lymphocyte:
i) Secretesantibodiesofthe same type into the blood
ii) Divided by mitosis to produce a clone
iii) Cells grow to form plasma cells producing masses
of free antibodies. Some of the cells remain in the
blood as memory cells.
Secondary response: this occurs if an individual is
exposed again to the same antigen. There is
immediate recognition and distraction - faster, larger
response usually prevents harm. Antibodies are
produced more rapidly and in larger amounts.
B- AND T-LYMPHOCYTES
 B-lymphocytes (B-cells) secrete antibodies
(humoral immunity)
 T-lymphocytes (T-cells) assist B-cells and may
attack infected cells (cell-mediated responses).
 Both cell types originate in the red bone marrow
from stem cells, but they undergo different
development processes in preparation for their
distinctive roles.
 B-lymphocytes then spread through the body
and settle in lymph nodes, although some
continue to circulate in the blood. T-lymphocytes
collect in the thymus gland, where they mature
before spreading into the same areas as B-
lymphocytes. The thymus gland disappears at
around the time of puberty. Both types of
lymphocyte have a large, rounded nucleus that
takes up most of the cell. They can only be told
apart by their different actions
 During the maturation process, any lymphocytes
that produce receptors that would bind with
those on the body’s own cells are destroyed.This
means that the remaining lymphocytes will only
act against non-self-molecules that are not
normally found in the body. Non-self-molecules,
such as those on the surfaces of invading
bacteria, are called antigens.
 Several different types of cell, including
macrophages, place antigens of pathogens they
have encountered in their cell surface
membranes,where there is a good chance that a
B-lymphocyte or T-lymphocyte may encounter
them.
These cells are called antigen-presenting cells.

An illustration of the process of formation of
lymphocytes
Action of B-lymphocytes
® A B-lymphocyte places some of its specific
receptor molecules in its cell surface membrane.
If it encounters an antigen that binds with this
receptor, the B-lymphocyte is activated. It
divides repeatedly by mitosis to produce a clone
of genetically identical plasma cells.
® Some of these synthesize and secrete large
quantities of proteins called immunoglobulins or
antibodies. The antibodies have the same
binding sites as the specific receptors in the B-
lymphocyte’s membrane, so they can bind with
the antigens. This may directly destroy or
neutralise the antigens, or it may make it easier
for phagocytes to destroy them.
® Some of the clone of B-lymphocyte cells become
memory cells. These remain in the blood for
many years. They are able to divide rapidly to
produce plasma cells if the same antigen invades
the body again.
® More antibody is therefore secreted more
rapidly than when the first invasion happened,
and it is likely that the pathogens will be
destroyed before they have a chance to
reproduce. The person has become immune to
this pathogen
AN illustration of action of B-lymphocytes
T-Lymphocytes: Cell-Mediated Response
 Cytotoxic lymphocytes defend against infection
in body cells. This occurs when a Virus enters a
cell thus more difficult to remove. No antibodies
involved / work directly on the infected cell by
destroying it.
 Special proteins called Major Histocompability
Complex (MHC) are present on all human cells.
Non-self-antigen interacts with MHC as human
cell becomes infected by a pathogen.
 Specific T-lymphocyte recognizes specific non-
self-antigen only with a chemical marker next to
it (MHC)
 Activated T-lymphocytes multiply by mitosis and
enter circulation
 Cells differentiate into different types of cell.
i) Cytotoxic T-Cells: destroy pathogens and infected
cells by enzyme action, and secrete chemicals which
attract and stimulate phagocytes.
ii) Helper T-Cells: stimulate the activity of the
cytotoxic T-Cells and B-lymphocytes by releasing

chemicals (cytokines/lymphokines and interleukins).
It’s the one destroyed by HIV.
iii) Suppressor T-Cells: switch off the T and B cell
responses when infection clears
iv) MemoryT-Cells:Some activatedT-Cellsremain in
the circulation and can respond quickly when same
pathogen enters body again.
Action of T-lymphocytes
 T-lymphocytes include T helper cells and T killer
cells. Both of these types of cell place their
specific receptors in their cell surface
membranes. On encountering the relevant
antigen, they are activated and divide by mitosis
to form a clone.
 Activated T helper cells secrete chemicals called
cytokines. These stimulate B-lymphocytes to
produce plasma cells, and stimulate monocytes
and macrophages to attack and destroy
pathogens.
 Activated T killer cells attach to body cells that
display the antigen matching their receptor.This
happens when a virus invades a body cell. The T
killer cell destroys the infected body cell
 Some of the clone of T cells become memory
cells, which remain in the body and can react
swiftly if the same pathogen invades again.
An illustration of the mechanisms of action of T-
lymphocytes
CELL MEDIATED IMMUNITY IN HUMANS
 Microorganisms bind onto receptor molecules
on the surface membrane of the T-lymphocytes.
They divide repeatedly/proliferate to form many
cells whichinclude T-helpercells;T-killercells and
T-suppressor cells.
 The T-helper cells produce large amount of
lymphokines which destroy the microorganisms
or stimulate T-cellsto multiply and produce more
lymphokinase or stimulate B-cells to produce
antibodies.
 The killer-T cells produce small amounts of
lymphokines which kill or destroy infected cells
with the viruses or cancer cells or transplanted
organs.
 Suppressor cells secrete lymphokinase which
decrease the activities of T-cells, white blood
cells and phagocytes.
Question: Describe the interactive role of
lymphocytes in adaptive immune responses (08
marks)
•Disease causingmicroorganisms produce antigens.
• Macrophages identify the antigen carrying
organism, chop off its piece and present it to a T4
(helper) cell.
•T4cells thenproduce lymphokines whichstimulate
multiplication of T and B- lymphocytes, promote
inflammation.
• B cell population undergoes clonal selection
forming two groups; plasma/effector cells and
memory cells.
• Plasma cells secrete anti bodies which destroy the
antigen carrying organism by; opsonization, lysis,
neutralization, precipitation or complement
activation.
Mechanisms used by pathogens to invade the
immune system.
•Antigenic variation;changing the structure of their
antigens so that they can’t bind to immune cells.
• Antigenic mimicry. Presenting antigens which
possess structures similar to self-proteins. The latter
cannot be attacked except during auto immune
syndromes.
• Immuno-suppression: Certain viruses reduce the
action of many immune cells and make it easy for
pathogen attack.
• Interference with cytokines: cytokines are
chemical signals between the humoral and cell
mediated pathways. Once they are blocked, the
systems fail to eliminate a pathogen.
• Complement inactivation: complement proteins
found in inactive form in the serum.When activated,

complements bring about a number of reactions
against microbes including inflammation reactions
and attraction of polymorphs or phagocytic cells into
the affected area.
NB: the roles of complement proteins in the body
defence against infections include the following:
1. Some attract phagocytes; by chemotaxis;
towards the area of infection;
2. Some coat bacteria; that allow phagocytes to
recognize; bind; and therefore engulf the
bacteria;
3. Some punch holes in the cell surface membranes
of bacteria; causing the bacterial cells to swell
and burst;
4. Some promote inflammation around a wounded
tissues; which attracts lymphokines to the
affected area;
Question: Briefly explain the features of HIV that
makes it a successful pathogen. (10 marks)
1. Antigenic variations/ change of antigens; due to
mutations;sothat it cannolongerbeidentified by
the white blood cells; hence it escapes being
removed from the body;
2. Long latency periods within the infected cells;
allows the spread of the viral DNA; without
triggering an immune response; and also protects
the virus from antiviral agents;
3. Attack on the CD4 cells; leads to improper
meditation of immune responses; weakening the
whole system making it unable to fight the virus;
4. It doesnot kill its host quickly; this provides more
time for its spread;
Types of immunity
These include the following;
1. Natural passive immunity
This involves passing antibodies in the body of an
organism into the body of another organism of the
same species e.g. from the mother to the foetus via
to the placenta to defend the body against disease
and also via the first milk called colostrum to the
child. This type of immunity is temporary.
2. Acquired passive immunity
This is the immunity in the body whereby the
antibodies in the body of an organism are extracted
and injected into the body to offer temporary
immunity e.g. the antibodies for tetanus.
3. Natural active immunity
This is the immunity that involves formation of
antibodies by the body of an organism in the
presence ofcertain antigens.This type of immunity is
permanent because during the immune response,
memory B-cells are produced which recognize the
microbes on reinfection (second infection) and then
stimulate the rapid production of large amounts of
antibodies to curb down the microbes before
causing significant damage. Memory B-cells stay for
long in blood.
4. Acquired active immunity
This involves introducing a small amount of antigens
(vaccines) orally or by injection into the body of an
organism to provoke and stimulate it to produce
corresponding antibodies. This results in rapid
immune response towards the living microbes in
case of an infection because of production of
memory B-cells which cause greater production of
many antibodies on second infection.
VACCINES
Vaccines are toxic chemicals or killed or attenuated
(weakened)microbes introduced into the body of an
organism to make it produce very many antibodies
against a certain pathogen.
The killed microbes are usually viruses and bacteria.
The attenuated microbes are living microbes which
are inactivated and they lack powers to infect the
body due to the chemical or temperature treatment
given to them.
Note; toxins are toxic chemicals produced by
microbes and therefore can work as antigens

A summary of the different types of immunity
RHESUS FACTOR (D-Antigens)
These are antigens which were first observed in the
bodies of the Rhesus monkeys of genus macaque.
These antigens are also carried on the surface of the
erythrocytes of some human beings. Those people
with D-antigensonthe surface of their redblood cells
are called Rhesus positive (Rh+
) while individuals
missing such D-antigens are called Rhesus negative
(Rh-
).
The bodies of individuals do not have already
manufactured antibodies against the D-antigens.
When an expectant mother who is Rh-
bears the
foetus with which is Rh+
, some foetal erythrocytes
with D-antigenswill cross the placenta andenter into
the blood circulation of the Rh-
mother towards the
end of the gestation period (pregnancy). It is also
possible for the blood of the foetus to mix with that
of the mother during birth so that the mother gets
Rh+
by getting the D-antigens from the child.
The D-antigensthathave enteredthe mother’sblood
circulation stimulate the maternal body to
manufacture corresponding antibodies (antibody-d
or anti-D antibodies) which attack and react with the
D-antigensin the mother. Some formed antibodies-d
can also pass via the placenta and enter the foetal
blood circulation where they attack and react with
the D-antigens which results into clumping together
and bursting of the foetal red blood cells,a condition
called erythroblastosis foetalis (Haemolytic disease
of the new born). This disease results into acute
anaemia which can lead to death of the feotus.
The first born rarely dies because the time is too
short for the mother to produce enough antibodies
that can pass to the foetus to cause death but
subsequent Rh+
foetus can die due to the many
antibodies of the mother entering its circulation to
cause agglutination.
Rh incompatibility does not affect pregnant women.
In a baby, it can cause hemolytic anemia. Hemolytic
anemia causes a baby’s red blood cells to be
destroyed faster than they can be replaced.
The effects of hemolytic anemia can range from mild
to severe. These effects may include jaundice, liver
failure, and heart failure
To prevent this disease, pregnant mothers are
always given anti-D chemicals 72hours to delivery, to
renderherimmune systeminsensitive towards the D-
antigen i.e. the mother may be infected with
antibody-d within 70-72hours to delivery or within 72
hours after herfirst born. Also, the blood of the fetus
can be transfused with normal blood to dilute
antibody-D so as to save the child.
How vaccines produce responses by the immune
system (Artificial active immunity)
Types of vaccine
1. Vaccine containing dead pathogens. Antigen is still
recognized and an immune response made
 Salk polio vaccine (Polio vaccine is injected)
 Influenza
 Whooping cough
2. Vaccine containing a toxin
 Diphtheria
 Tetanus
3. Vaccine containing an attenuated (modified or
weakened) organism which is alive but has been
modified so that it is not harmful
 Sabin polio vaccine (Taken orally, often
sugar pumps)
4. Purified antigen - genetically engineered vaccine.
o Hepatitis B (A gene coding for a surface
protein of the hepatitis B virus has been
inserted into yeast cells which produce the
protein when grown in fermenters)
Transplantation

This is the replacement of diseased tissue or organs
byhealthy onesthrough a surgery.It’sless successful
than blood transfusion because the organ contains
more antigens than blood so they are likely to be
rejected by the body’s immune system. Tissue
rejection has been perfectly overcome by:
® Careful tissue typing i.e. using tissue which
meets the donor and recipient antigens as
exactly as possible.
® Use of immune suppressive drugs which
suppress the recipient’simmunity inorder to
increase the chances of transplant success.
Tissue typing canbe effectedthrough the following
ways;
i) Autograft; the tissue is grafted from one area to
another on the same individual. E.g.skin. Rejectionis
not a problem.
ii) Isograft; a graft betweentwo genetically identical
individuals’ e.g. identical twins. Rejection is not a
problem.
iii) Allograft; a tissue from individual to individual but
the two must be closely attached or related though
of different geneticconstitution. In case of rejection,
immune suppressive drugs can be used.
iv) Xenograft; a graft between individuals of
different species such as from sheep to human.

Uptake and transport in plants updated 2020

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