Good for introductory plant physiology

1. BIO 2203: INTRODUCTORY
PLANT AND ANIMAL
PHYSIOLOGY AND HISTOLOGY
Dr. Omony John Bosco

2. Part A: What is a plant?
Definition - by most definitions, a plant:
 is multicellular;
 is non-motile
 has eukaryotic cells
 has cell walls comprised of cellulose
 is autotrophic; and
 exhibits alternation of generations - has a distinctive diploid (sporophyte) and
haploid (gametophyte) phase.
• Examples - the Plant Kingdom includes the angiosperms (flowering plants),
gymnosperms (cone-bearing plants), ferns, and bryophytes (mosses & liverworts).
• Recent classification systems suggest that these organisms, in addition to the
red algae and green algae, should be classified in the Plant Kingdom (Plantae).

3. PLANT PHYSIOLOGY
Plant physiology deals with various functions and processes occurring
in plants. For examples; metabolism, water relations, mineral nutrition,
development, movement, irritability study(response to the
environment), growth, and transport processes.
Definitions (numerous) - Plant physiology is the study of:
 the functions and processes occurring in plants
 the vital processes occurring in plants
how plants work
• In essence, plant physiology is a study of the plant way of life, which
include various aspects of the plant lifestyle and survival including:
metabolism, water relations, mineral nutrition, development,
movement, irritability (response to the environment), organization,
growth, and transport processes

4. Cont……….
• These functions are performed by the protoplasm. Maintenance of life and
activity of protoplasm requires the following;
- Water for absorption of inorganic materials from the soil, provides
medium for the transportation of gases and soluble food in plants. Many
chemical changes are also carried out in solution in the plant body.
- Air, plants require oxygen for respiration and carbon dioxide for
manufacturing food.
- Optimum heat of about 30oC maintains high activities of the protoplasm
and all vital processes carried out on it, since most physiological
processes are controlled by enzymes.
- Light has a stimulating effect on growth, it’s responsible for green
coloration of plants, utilization of carbon dioxide of air and manufacturing
of sugar and starch.
- Food for its nutrition.
Therefore, plant physiology is the study of life processes of plants

5. Why study plant physiology?
• Food source: Plants are the route by which solar energy enters
ecosystems
• Economically important products: Plants produce countless products
such as fibres, medicines and wood.
• Applications to other disciplines: Applicable in agriculture, chemistry,
forestry, horticulture etc.
• Career purpose: Industries, research institutes, Jobs! etc
• Theoretical importance In application of the theories and knowledge
obtained to explain other related fields –
Botany Without Borders is a good online film that highlights the
importance of plants. It was created by Dr. K Niklas (Cornell).
How can you become a plant physiologists?
• Go through undergraduate training
• Join professional societies
• Read plant physiology and do related researches
• Perform tasks in several careers.

6. PLANT CELLS AND TISSUES
•A tissue is a group of cells of the same type or of the mixed type, having a
common origin and performing an identical function.
• Tissues are classified into two groups as illustrated below:
i. Meristematic tissues composed of cells that are in a state of division or
retain the power of dividing to produce daughter cells which grow and
form the rest of the plant body
ii. Permanent tissues composed of cells that have lost the power of
dividing having attained their definite form and size.
iii. Parenchyma tissues. Consists of collection of living cells which are oval
and spherical in transverse section; polygonal and elongated in
longitudinal section as shown below.

7. Adaptations to functions of parenchyma cells
• Parenchyma cells which contain chloroplasts (are called chlorenchyma)
manufactures sugar and starch.
• Large vacuole which stores large quantities of sap which maintains
turgidity of the young shoot especially herbaceous plants.
• The cells are unspecialized which make them act as packing tissues
between
more specialized tissues e.g. in central pith of stems and outer cortex of
stems and roots.
• The turgid cells during the periods of water shortage lose water resulting
in wilting of the plants. This leads to closure of stomata in the leaves hence
reduced rate of water loss by transpiration.
• The cells are metabolically active, thus sites of many vital activities of the
plant body. They may also store food e.g. in potato tubers.

8. Cont……
• The air spaces between the living cells are for gaseous exchange between
the cells and their external surrounding environment.E.g.in the spongy
mesophyll layer of the leaves. Oxygen for respiration and carbondioxide for
photosynthesis can diffuse through the airspaces along concentration
gradient
• The cell walls are made of cellulose, pectins, hemicelluloses which allow
water and mineral salt transport through the plant.

9. Collenchyma.
• Collenchyma consists of living cells modified to give support and
Mechanical strength.
• Their cells are elongated and polygonal with tapering ends, the corners of
the cell are deposited with extra cellulose and pectin to provide mechanical
function/support. However, some of the cells contain chloroplasts for
manufacturing sugars and starch.

10. Sclerenchyma.
• The mature cells are dead due to heavy deposition of lignin, therefore
providing great support and mechanical strength for the plant
Xylem and Phloem
They constitute the vascular tissue of the plant. Both of them contain more
than one type of cells as described below.
Xylem
• The xylem consists of four cell types, i.e tracheids, vessel elements,
parenchyma and fibres.
• Xylem as a whole is for conduction of water and mineral salts upwards
from the roots to the leaves. Tracheids and vessels have empty lumen for
Passage of water without being destructed by living contents. The lignified
walls are perforated with numerous pits to permit passage of water in and
out of the lumen.

11. Cont……
• Tracheid walls are usually provided with one or more rim of bordered pits
for controlling passage of water.
• Xylem also gives mechanical strength to the plants body. Vessels have thick
walls which are lignified for strengthening the plant body.
• The ray parenchyma is more extensive and forms radial sheets of tissues
called medullary rays which maintain a living link through the wood between
the cork and the pith for food storage; deposition of tannins, crystals; radial
transport of food and water; gaseous exchange through the intercellular
spaces.

12. PHLOEM
•There are five cell types in the phloem i.e sieve tube elements, companion
cells, parenchyma, fibres and sclereids.
In the sieve tubes and companion cells;
-The sieve pores allow the flow of solution(organicsolutese.gsucrose)
from one element to the next.
-Secondary phloem is crossed by bands of lignified fibres and medullary rays
of parenchyma for transportation of materials across cells.

13. Phloem parenchyma, fibres and scleroids
• Phloem parenchyma and fibres are found in dicotyledons but not in
monocotyledons.
• Phloem parenchyma cells are much more elongated though the general
structure functions (primary and secondary) are the same as those of
parenchyma cells of xylem already discussed earlier
• Phloem fibres are exactly the similar to the sclerenchyma fibres already
described. They occur occasionally in the primary phloem, but more
Frequently in the secondary phloem of dicotyledons, where they form
Vertical running bands of cells to resist pressure on the phloem as it
stretches during growth.
• Scleroids has been already discussed, occur frequently in especially older
phloem.

14. PLANT-WATER R ELATIONS
Water is the main constituent of all living plant cells. However, water content
of plant cells varies depending on the type & physiological status of the cells
e.g;
• Most plants are comprised of atleast 70% water, e.g. lettuce leaves
constitute about 95% water
• However, some dormant plant organs e.g. seeds & buds have less than
10% water
• Water is therefore essential for chemical transformation in plants
• The limiting resource for crop productivity in most agricultural systems.

15. Physical and chemical properties of water
Chemical properties of water:
Polarity
•Water is important because it readily forms hydrogen bonds (i.e. a
positively-charged hydrogen atom attracted to a negatively-charged
oxygen atom)
•A hydrogen bond is a weak bond that forms between a hydrogen atom
covalently bonded to two electronegative oxygen atoms
• Thus water readily forms hydrogen bonds with other polar molecules
•The attraction of hydrogen bonds between water molecules is termed as
cohesion.
•The attraction between water molecules and other molecules is called
adhesion (i.e., when a paper towel absorbs water, water and cellulose
adhere to one another).

16. Cont……
•Cohesion and adhesion are responsible for capillary action, i.e. the
movement of water up a stem or thin column.
•Polarity dissolves other molecules e.g NaCl so that ions are easily taken up
by plants
Solvent
•A universal solvent hence dissolves more substances than any other salts
due to small size & high dielectric constant (i.e. high degree of transmitting
electric fields) that weakens forces between elements such as sodium (Na+,
Cl-), hence the ions formed can be easily absorbed by the plants. Hydrophilic
substances dissolve readily while hydrophobic ones do not.
•Water doesn't react since it’s chemically inert; this makes it a medium of
other metabolic reactions and does not interfere with them.

17. Cont….
Note: Water dissociation into hydrogen ions and hydroxyl ions is the
basis for pH system during formation of equilibrium constant, vital for
enzymatic activities in plant