Chapter 9 transport in plants lecture

1. Chapter 9 Transport in Plants

2. How is water transported
against gravity from the
roots, up the xylem and
to the leaves?

3. I wonder where
trees get water
from?
Well,
obviously
from the
ground.
What are the
processes involved?

4. How does water move
through the transport
system of a plant IF
it does not have a heart
to act as a pump?
PAUSE to
PONDER
•How is water lifted
against gravity from the
ground to the leaves
through this transport
system?
• Are the products of
photosynthesis also
carried in a set of vessels 4

5. Diagram of Xylem Vessel

6. Transport Structures of Flowering
Plants
1) Xylem
• Consists of mainly xylem vessels that are
made up of dead cells.
• Inner walls of xylem vessels are
strengthened by lignin.
• Lignin deposited in the form of rings or
spirals.

7. 1) Xylem (cont)
• Function:
– Conduct water and mineral salts from
roots to stems and leaves.
– Provide mechanical support for plant.
Transport Structures of Flowering
Plants

8. Adaptations of the xylem vessel for its
function
1) Empty lumen, no protoplasm or cross-walls.
– Reduces resistance to water flowing through
2) Walls thickened with lignin.
– Lignin is a hard and rigid substance.
– Prevents collapse of the vessel
(Mechanical support)

9. 2) Phloem
• Consists mainly of sieve tubes and companion
cells.
• Sieve tube consists of columns of sieve tube
cells, that are elongated and thin-walled.
• Companion cells provide the nutrients and help
the sieve tube cells transport manufactured food.
(Sucrose)
Transport Structures of Flowering Plants

10. Diagram of Phloem

11. 2) Phloem (cont)
• Function:
– Conducts manufactured food (sucrose and
amino acids) from the leaves to the other parts of
the plant.
Transport Structures of Flowering Plants

13. Monocotyledon VS Dicotyledon

14. 1 Vascular bundles
14
How Are the Vascular Tissues Organised
in Stems?
In a dicotyledonous stem, the xylem
and phloem are grouped together to
form vascular bundles.
xylem
cambium
phloem
vascular bundle
The phloem lies outside the xylem with
a tissue called the cambium between
them.
•Cambium cells can divide and
differentiate to form new xylem and
phloem tissues,
•Giving rise to a thickening of the stem.
2 Cambium

15. How Are the Vascular Tissues Organised in
Stems?
Pith
The vascular bundles are arranged
in a ring around a central region
called the pith.
3
Cortex
4
The region between the vascular
bundles and the epidermis is the
cortex.
•Both the cortex and the pith serve
to store up food substances, such
as starch.

16. How Are the Vascular Tissues Organised in
Stems?
Epidermis
The stem is covered by a layer of
cells called the epidermis.
•The epidermal cells are protected
by a waxy, waterproof cuticle
•Which greatly reduces evaporation
of water from the stem.
5

17. 2 Pith
1 Vascular Bundles
3
4 Cortex
5 Epidermis
Xylem
Cambium
Phloem
Vascular
bundle
17
How Are the Vascular Tissues Organised in
Stems?

18. How Are the Vascular Tissues Organised in
Roots?
xylem
phloem
In a dicotyledonous root, the
xylem and phloem are not
bundled together. Instead, they
alternate with each other.
1 Vascular bundles
2 Cortex
The cortex of the root is also a
storage tissue. The innermost
layer of root cortex is called the
endodermis.

19. How Are the Vascular Tissues Organised in
Roots?
Piliferous layer
The epidermis of the root is the
outermost layer of cells. It bears
root hairs. It is also called the
piliferous layer.
Root hair
Each root hair is a tubular
outgrowth of an epidermal cell.
•This outgrowth increases the
surface area to volume ratio of the
root hair cell.
•The absorption of water and
mineral salts is increased through
this adaptation.
4
3

20. 1 Xylem and phloem alternate with
each other.
2 Cortex
Endodermis
3 Piliferous layer
4 Root hair
20
How Are the Vascular Tissues
Organised in Roots?

21. How Are the Vascular Tissues
Organised in Leaves?

22. Distribution of vascular bundles in leaves.
xylem
phloem

23. xylem
phloem
Diagram showing a
section through a leaf.

24. How you ever noticed such dots on
tree trunks? WH AT IS IT?

25. Formation of Lenticles
• In woody stems the stomata are blocked by the
presence of cork cells
• The epidermis of woody stems breaks up to form tiny
pores called lenticles which allow gaseous exchange.

26. Test yourself! (pg.179)
• Qn 1

27. The Journey so far…
• Xylem
– Structure: Arrangement of lignin
– 2 functions
– 2 adaptations
• Phloem
– Structure: Made of ? & ?
– Function
– Adaptation
• Arrangements of X & P (VB) in roots,
stems, leaves

28. Lesson Objectives
• Movement of substances and the
processes involved in the roots and leaves

29. 29
cytoplasm
vacuole
nucleus
cell wall
cell surface membrane
of root hair cell
film of liquid
(dilute solution
of mineral salts)
soil particles
Entry of Water into a Plant

30. Entry of Water into a Plant
30
A
B
C
xylem
phloem cortex
root hair
piliferous layer
A section of
root
showing the
path of
water
through it

31. 31
cytoplasm
vacuole
nucleus
cell wall
cell surface membrane
of root hair cell
film of liquid
(dilute solution
of mineral salts)
soil particles
Each root hair is a fine tubular outgrowth of an
epidermal cell.
•It grows between the soil particles,
•Coming into close contact with the water
surrounding them.
1
Entry of Water into a Plant
1

32. 32
cytoplasm
vacuole
nucleus
cell wall
cell surface membrane of root
hair cell
film of liquid
(dilute solution
of mineral salts)
soil particles
1
Entry of Water into a Plant
2
The thin film of liquid surrounding
each soil particle is a dilute solution
of mineral salts.
2

33. Entry of Water into a Plant
33
The sap in the root hair cell is a relatively concentrated solution of
sugars and various salts.
•Thus the sap has a lower water potential than the soil solution.
• These two solutions are separated by the partially permeable cell
surface membrane of the root hair cell.
• Water enters the root hair by osmosis.
3
A
B
C
xylem
phloem cortex
root hair
piliferous layer
water entering
the root hair
A section of root showing
the path of water through
it
3

34. Entry of Water into a Plant
34
The entry of water dilutes the sap.
• The sap of the root hair cell now has a higher water potential
than that of the next cell (cell B)
• Hence, water passes by osmosis from the root hair cell into the
inner cell.
4
A
B
C
xylem
phloem
cortex
root hair
piliferous layer
water entering the
root hair
A section of root showing the
path of water through it
3
4

35. Entry of Water into a Plant
35
Similarly, water passes from cell B into the next cell
(cell C) of the cortex.
•This continues until the water enters the xylem vessels
and moves up the plant.
5
A
B
C
xylem
phloem
cortex
root hair
piliferous
layer
water entering the
root hair
A section of root
showing the path of
water through it
3
4
5

36. How do nitrate ions
get into plants?
Are they directly
absorbed from the
air?
No. Even though
the air has 79% of
nitrogen, it is
highly unreactive.
PAUSE to
PONDER
•How are ions transported around in
plants?

37. How do root hairs absorb ions and mineral
salts?
1) Active Transport
• When the concentration of ions in the salt solution
is lower than that in the root hair cell sap
• Root hairs absorb the salts against a concentration
gradient
• Energy for this process comes from cellular
respiration in the root hair cell.

38. 2) Diffusion
• When concentration of certain ions in the soil
solution are higher than that in the root hair cell.
How do root hairs absorb ions and mineral
salts?

39. How the root hair cell is adapted to its
function of absorption
1) Root hair is long and narrow
• Increases surface area to volume ratio
• Which in turn increases the rate of absorption of
minerals and water.
2) Cell surface membrane prevents cell sap from
leaking out
• Cell sap contains sugars, amino acids and salts
• Has lower water potential than soil solution
• Results in water entering the root hair by osmosis

40. 3) Living root hair cell
• Able to provide energy for active transport of ions
(mineral salts) into the cell.
• Energy produced by the mitochondria during
cellular respiration.
How the root hair cell is adapted to its
function of absorption

41. Movement of
Water inside
a Leaf
41
Cuticle
Film of water
Xylem
Phloem
Intercellular air space
Upper
epidermis
Palisade
mesophyll
Spongy
mesophyll
Lower
epidermis
Guard cell
Stomatal pore

42. Movement of
Water inside
a Leaf
42
Cuticle
chloroplast
s
Nucleus
Film of
water
Xylem
of vein
Phloem
Intercellular
air space
Sub-stomatal
air space
Upper epidermis
Palisade
mesophyll
Spongy
mesophyll
Lower
epidermis
1
arrows show path
of water vapour
and water
Guard cell
Stomatal pore
Cell sap
Water
continuously
moves out of the
mesophyll cells to
form a thin film of
moisture over
their surfaces.
1

43. 43
cuticle
chloroplast
s
nucleus
film of
water
xylem of
vein
phloem
intercellular
air space
sub-stomatal
air space
upper epidermis
palisade
mesophyll
spongy
mesophyll
lower
epidermis
1
guard cell
Water evaporates from
this thin film of moisture
• moves into the
intercellular air spaces.
• Water vapour
accumulates in the large
air spaces near the
stomata (sub-stomatal air
spaces).
2
2
stomatal pore
Movement of
Water inside
a Leaf

44. Movement of
Water inside
a Leaf
44
cuticle
chloroplasts
nucleus
film of
water
xylem of
vein
phloem
intercellular
air space
sub-stomatal
air space
upper
epidermis
palisade
mesophyll
spongy
mesophyll
lower
epidermis
1
guard cell
cell sap
2
Water vapour then
diffuses throughout the
stomata to the drier air
outside the leaf. This is
transpiration.
3
3
stomatal pore

45. 45
cuticle
chloroplasts
nucleus
film of
water
xylem of
vein
phloem
intercellular
air space
sub-stomatal
air space
upper epidermis
palisade mesophyll
spongy
mesophyll
lower
epidermis
1
guard cell
2
stomatal pore
Movement of
Water inside a
Leaf
3
4
cell sap
As water evaporates from
the mesophyll cells,
• the water potential of the
cell sap decreases.
• The mesophyll cells begin
to absorb water by osmosis
from the cells deeper inside
the leaf.
• These cells, in turn,
remove water from the vein,
that is, from the xylem
vessels.
4

46. 46
cuticle
chloroplasts
nucleus
film of
water
xylem of
vein
phloem
intercellular
air space
sub-stomatal
air space
upper epidermis
palisade mesophyll
spongy
mesophyll
lower
epidermis
1
guard cell
2
stomatal pore
Movement of
Water inside
a Leaf
3
4
cell sap
This results in a suction
force which pulls the
whole column of water up
the xylem vessel.
5

47. Transpiration
Definition:
It is the loss of water vapour through
the stomata of the leaves.

48. Importance of Transpiration
1) Transpiration pull
• helps to draw water and mineral salts from the
roots to the leaves
2) Evaporation of water removes latent heat
from the plant.
• prevent the plant from overheating
3) Water transported to the leaves can:
• be used for photosynthesis
• keep cells turgid
• replace water lost by the cells.

49. Factors affecting the rate of
Transpiration
1) Humidity of the air
• Humidity refers to the amount of water vapor in
the air.
• Increasing humidity decreases the concentration
gradient between air and leaf.
• Therefore, deceasing the rate of transpiration
2) Wind or Air movement
• The stronger the wind, the faster the rate of
transpiration.

50. 3) Temperature of air
• Increasing temperatures increases the rate of
evaporation.
• Thus increasing the rate of transpiration
4) Light
• Light affects the stomata.
• With increasing light intensity, stomata open and
become wider.
• Therefore, this increases the rate of transpiration
Factors affecting the rate of
Transpiration

51. Wilting

52. Wilting
• Occurs when excess transpiration occurs
• In strong sunlight, rate of transpiration exceed
rate of water absorption by the roots
• cells lose more water than they absorb water,
resulting in plasmolysis  water leaves the cells,
causing the cell membrane to shrink from the
cellulose cell wall
• cells lose their turgor pressure and become
flaccid
• This results in the plant wilting.

53. Advantages of Wilting
• The folding up of the leaves
– Surface area exposed to sunlight is reduced
• Leads to the guard cells becoming flaccid and close
up
– Therefore reducing the rate of transpiration

54. Disadvantages of Wilting
• Water is the limiting factor for photosynthesis
• Stomata is closed,
– Amount of CO2 entering the leaf is also reduced.
– CO2 becomes a limiting factor,
• Therefore decreasing the rate of photosynthesis.

55. Experiments

56. Investigation 9.1

58. • What is transverse?
• Which tissue has been stained red?
• What conclusion can you draw from your
investigation?

59. Investigation 9.2
• Make drawings of your observations
• What does this experiment tell you about
the phloem?
• Suggest an explanation of your
observations.

60. Investigation 9.2
• The phloem tissues have been removed.
• Manufactured food substances (e.g sugar and amino acid)
accumulate above the cut region and cause swelling in twigs A and C.
However in twig B, manufactured food can pass through the phloem
without any barrier.
• This suggests that food is made in the leaves and are transported
through the phloem.
twig A twig B twig C