1. CHAPTER 09
Transport in Plants 1

2. 9.1 The Transport Structures of Flowering Plants
Chapter 9
Transport in Plants
9.1 The Transport Structures of Flowering Plants
9.2 Studying the Movement of Substances in Plants
9.3 Entry of Water into a Plant
9.4 Moving Water against Gravity 2

3. The Transport Structures of Flowering Plants 9.1
Learning Outcomes
After this section, you should be able to:
identify the positions of xylem and phloem tissue in a dicotyledonous leaf and stem; and
explain the functions of xylem and phloem tissue. 3

4. The Transport Structures of Flowering Plants 9.1
LEAF
STEM
ROOT
dermal tissue
ground tissue
vascular tissue
Diagram showing the dermal, ground and vascular tissue systems in plants 4

5. There are two types of vascular tissues: Xylem vessels Phloem vessels
The Transport Structures of Flowering Plants
9.1
There are two types of vascular tissues:
Xylem vessels
Phloem vessels
(sieve tube elements
and companion cells) 5

6. The Transport Structures of Flowering Plants 9.1
In a stem
xylem vessels
phloem 6

7. Conducts water and mineral salts from the roots to the stem and leaves
The Transport Structures of Flowering Plants
9.1
Functions of xylem
Conducts water and mineral salts from the roots to the stem and leaves
Provides water for the plant 7

8. Has a continuous lumen with no cross- walls or protoplasm
The Transport Structures of Flowering Plants
9.1
Structure of xylem
A xylem vessel is made up of many dead cells fused together at the ends to form a long hollow tube.
Has a continuous lumen with no cross- walls or protoplasm
Lignin deposits in the inner walls of xylem vessels 8

9. Why do you think there are different patterns of lignifications?
The Transport Structures of Flowering Plants
9.1
Why do you think there are different patterns of lignifications?
Allows water to go to the side of the plant
transverse section of a pitted xylem vessel
annular
spiral
pitted
Other forms-
scalariform
reticulate 9

10. How is the xylem adapted for its function?
The Transport Structures of Flowering Plants
9.1
How is the xylem adapted for its function?
Empty lumen without protoplasm or cross-walls enables water to move easily through the lumen
Walls are lignified to prevent the collapse of vessels 10

11. The Transport Structures of Flowering Plants
9.1
Function of phloem
Transports manufactured food (sucrose and amino acids) from the leaves to other parts of the plant 11

12. Structure of phloem (sieve tube)
The Transport Structures of Flowering Plants
9.1
Structure of phloem (sieve tube)
Sieve tube cells are elongated cells that lack nuclei and have thin layers of cytoplasm
Sieve tube elements are made of sieve tube cells that are joined end to end to form a column with sieve plates in between.
Sieve plates are cross-walls with many small sieve pores.
Sieve tube cells have no nucleus but are living-used to carry food -are bidirectional
Companion cell used to maintain sieve tube cells 12

13. Structure of phloem (companion cell)
The Transport Structures of Flowering Plants
9.1
Structure of phloem (companion cell)
Narrow, thin-walled cell with cytoplasm, nucleus and numerous mitochondria 13

14. The Transport Structures of Flowering Plants 9.1
degenerate protoplasm within sieve tube cells
sieve plates with sieve pores
companion cell
Diagram showing L.S. and T.S. of phloem 14

15. How is the phloem adapted for its function?
The Transport Structures of Flowering Plants
9.1
How is the phloem adapted for its function?
Phloem sieve tube elements have very little protoplasm and are arranged to form a continuous column. This reduces the resistance to the flow of substances within the phloem.
Pores within the sieve plates allow rapid flow of manufactured food substances 15

16. How is the phloem adapted for its function?
The Transport Structures of Flowering Plants
9.1
How is the phloem adapted for its function?
Companion cells have numerous mitochondria to produce energy for the loading of sugars into the phloem sieve tubes.
Every phloem sieve tube cell has an associated companion cell to ensure its survival. 16

17. How are the vascular tissues organised in stems?
The Transport Structures of Flowering Plants
9.1
How are the vascular tissues organised in stems? 1
In a dicotyledonous stem, the xylem and phloem are grouped together to form vascular bundle. 2
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.
phloem
xylem
cambium
The vascular bundles are arranged in a ring around a central region called the pith. 3
vascular bundle 17

18. How are the vascular tissues organised in stems?
The Transport Structures of Flowering Plants
9.1
How are the vascular tissues organised in stems? 1
vascular bundles
Collateral 2
cambium
pith 3
The stem is covered by a layer of cells called the cuticle. The epidermal cells are protected by a waxy, waterproof epidermis that greatly reduces evaporation of water from the stem. 4 5
The region between the vascular bundles and the epidermis is the cortex. Both the cortex and the pith are storage tissues.
Vascular Bundle 18

19. How are the vascular tissues organised in stems?
The Transport Structures of Flowering Plants
9.1
How are the vascular tissues organised in stems? 1
vascular bundle
phloem
cambium
xylem 2
pith 3 4
epidermis
cortex 5 19

20. How are the vascular tissues organised in roots?
The Transport Structures of Flowering Plants
9.1
How are the vascular tissues organised in roots?
In a dicotyledonous root, the xylem and phloem are not bundled together. They alternate with each other. 1
xylem
phloem
The cortex of the root is a storage tissue. The innermost layer of root cortex is called the endodermis. 2
cortex
endodermis
Protects inner organells 20

21. How are the vascular tissues organised in roots?
The Transport Structures of Flowering Plants
9.1
How are the vascular tissues organised in roots? 3
The epidermis of the root is the outermost layer of cells. It is also called the piliferous layer.
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. 4
Not a new cell but just an extension/growth 21

22. How are the vascular tissues organised in roots?
The Transport Structures of Flowering Plants
9.1
How are the vascular tissues organised in roots?
xylem and phloem alternate with each other 1 4
root hair
cortex 2
piliferous layer 3 22

23. 9.1 The Transport Structures of Flowering Plants
Chapter 9
Transport in Plants
9.1 The Transport Structures of Flowering Plants
9.2 Studying the Movement of Substances in Plants
9.3 Entry of Water into a Plant
9.4 Moving Water against Gravity 23

24. Studying the Movement of Substances in Plants 9.2
Learning Outcomes
After this section, you should be able to:
state that translocation is the transport of food substances in phloem; and
describe experiments that provide evidence to the function of xylem in transporting water and the function of phloem in transporting food substances. 24

25. Studying the Movement of Substances in Plants 9.2
What is translocation?
Translocation is the transport of manufactured food substances, e.g. sucrose and amino acids, in plants.
It is bi-directional. Food substances can move either down the phloem tissues of the shoots to the roots, or up the phloem tissues of the shoots to the leaves. 25

26. Studying the Movement of Substances in Plants 9.2
Translocation studies
The characteristics of translocation can be studied using:
1) aphids
2) the ‘ringing’ experiment
3) radioactive carbon isotopes 26

27. Using aphids Studying the Movement of Substances in Plants 9.2
Anaesthetise the aphid with CO2 while it is feeding on a stem.
Cut off its body such that its proboscis remains in the plant tissue.
Analyse the liquid that exudes from cut end of proboscis.
Section the portion of the stem that contains the proboscis and examine it under a microscope. 27

28. Using aphids Studying the Movement of Substances in Plants 9.2
Why is it necessary to anaesthetise the aphid while it is feeding?
Answer:
To enable the body of the aphid to be cut off while the aphid is still feeding. This ensures that the proboscis remains in the phloem sieve tube.. 28

29. Using aphids Studying the Movement of Substances in Plants 9.2
What tests can we use to analyse the contents of the liquid that exudes from the cut end of proboscis?
Answer:
The following food tests can be used to determine the contents of the liquid:
Biuret’s test for proteins,
Benedict’s test for reducing sugar, and
Ethanol emulsion test for fats.. 29

30. Using aphids Studying the Movement of Substances in Plants 9.2
Why do we section the stem, at the region where the proboscis is, for examination under a microscope?
Answer:
To determine which tissue the proboscis was inserted into. 30

31. Using the ‘ringing’ experiment
Studying the Movement of Substances in Plants
9.2
Using the ‘ringing’ experiment
Cut off a complete ring of bark from the main stem of a woody twig A. The ring is above the water level. A B
region with bark removed
unringed twig
water 31

32. Using the ‘ringing’ experiment
Studying the Movement of Substances in Plants
9.2
Using the ‘ringing’ experiment
Set up a control using an unringed twig B.
Ensure that the bottom end of both twigs are in contact with water.
Observe the twigs daily. A B
region with bark removed
unringed twig
water
Predict the appearance of twigs A and B after a week. 32

33. Using the ‘ringing’ experiment
Studying the Movement of Substances in Plants
9.2
Using the ‘ringing’ experiment
Answer: A B
region with bark removed
unringed twig
water
Twig A after 1 week 33

34. Using the ‘ringing’ experiment
Studying the Movement of Substances in Plants
9.2
Using the ‘ringing’ experiment
Suggest an explanation for the observation.
Answer:
The removal of phloem prevents the translocation of sugars to the region below the ring, resulting in an accumulation of sugars. This accumulation of sugars lowers the water potential of the cells in the region, causing water to enter the region causing the region to cell. 34

35. Using radioactive carbon isotope
Studying the Movement of Substances in Plants
9.2
Using radioactive carbon isotope
Supply radioactive carbon (14C) to an intact leaf enclosed in a sealed chamber.
Allow photosynthesis to take place.
Cut a section of the stem and expose it onto an X-ray photographic film. 35

36. Using radioactive carbon isotope
Studying the Movement of Substances in Plants
9.2
Using radioactive carbon isotope
Predict the regions where radioactivity would be detected.
Answer:
Carbon-14 radioactivity will be detected in the phloem. 36

37. Studying the pathway of water
Studying the Movement of Substances in Plants
9.2
Studying the pathway of water
Allow a young plant to stand in a dilute red ink solution.
After a few hours, cut a transverse section of the stem and a transverse section of a portion of the root that was not immersed in ink. 37

38. Studying the pathway of water
Studying the Movement of Substances in Plants
9.2
Studying the pathway of water
Predict which tissue would be stained red in the transverse section of the stem and root.
What conclusion can be drawn?
Water is drawn up the xylem vessels. 38

39. 9.1 The Transport Structures of Flowering Plants
Chapter 9
Transport in Plants
9.1 The Transport Structures of Flowering Plants
9.2 Studying the Movement of Substances in Plants
9.3 Entry of Water into a Plant
9.4 Moving Water against Gravity 39

40. Entry of Water into a Plant 9.3
Learning Outcomes
After this section, you should be able to:
explain how water enters the root and moves between root cells; and
relate the structure of root hairs to its function in water and ion uptake. 40

41. How does water enter a plant?
Entry of Water into a Plant
9.3
How does water enter a plant?
soil particles
Root hairs grow between the soil particles. They are in close contact with the surrounding soil particles. 1
root hair 41

42. How does water enter a plant?
Entry of Water into a Plant
9.3
How does water enter a plant?
Each soil particle has a thin film of liquid surrounding it. The soil solution is a dilute solution of mineral salts. 2
The sap in the root hair cell is more concentrated due to the presence of sugars and mineral salt; it has a lower water potential than the soil solution. Hence, water enters the root hair by osmosis. 3 42

43. How does water enter a plant?
Entry of Water into a Plant
9.3
How does water enter a plant?
root hair C B A 3
The entry of water dilutes the root hair cell 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 43

44. How does water enter a plant?
Entry of Water into a Plant
9.3
How does water enter a plant?
Similarly, water passes from cell B into the next cell (cell C). This process continues until the water enters the xylem vessels. 5 C B A
xylem
root hair
cortex 44

45. Entry of Water into a Plant 9.3
How is the root hair cell adapted for its
function?
It is long and narrow with a large surface area-volume ratio. This increases the rate of absorption.
Presence of endodermis layer and cell membrane prevents leakage of cell sap and allows water to enter the cell by osmosis down the water potential gradient. 45

46. Entry of Water into a Plant 9.3
Mineral salts are absorbed into root hair cells by:
Diffusion
When the concentration of ions is higher in the soil solution than in the root hair cell, ions diffuse into the root hair cell.
Active transport
When the concentration of ions is higher in the root hair cell than the soil solution, ions are taken into the cell with the use of energy. 46

47. Entry of Water into a Plant 9.3
Thinking question:
Why is water and mineral ions absorption decreased in water-logged soil?
Answer:
Water-logged soil has a very dilute soil solution. This lowers the concentration of ions and the root hair cell is unable to absorb mineral ions. This affects the absorption of water as the cell sap would not have much mineral ions. Therefore, the water potential gradient would be less steep. This mean that less water will be absorbed by osmosis. 47

48. 9.1 Transport Structures of Flowering Plants
Chapter 9
Transport in Plants
9.1 Transport Structures of Flowering Plants
9.2 Movement of Substances in Plants
9.3 Entry of Water into a Plant
9.4 Moving Water against Gravity 48

49. Moving Water against Gravity 9.4
Learning Outcomes
After this section, you should be able to:
outline the pathway in which water travels from the roots to the leaves;
understand and explain what transpiration is; and
explain how various factors affect the rate of transpiration. 49

50. Moving Water against Gravity
9.4
What is root pressure?
Root pressure is pressure resulting from the constant entry of water into the roots. 50

51. What is capillary action?
Moving Water against Gravity
9.4
What is capillary action?
Tendency of water to move up inside very narrow tubes
Depends on the forces of cohesion and adhesion.
URL 51

52. Moving Water against Gravity
9.4
What is transpiration?
It is the loss of water from the aerial parts of the plant, especially through the stomata of the leaves. 52

53. Moving Water against Gravity 9.4
Where does transpiration occur?
Set up the experiment shown below and observe the water levels of A and B after several hours.
oil
water A
B (control) 53

54. Moving Water against Gravity 9.4
Observation
After several hours the water level in A would have decreased, while the water level in B would have remained unchanged.
water level A
B (control) 54

55. Moving Water against Gravity 9.4
Conclusion
This experiment demonstrates that transpiration occurs mainly through the leaves of a plant.
water level A
B (control) 55

56. What is transpirational pull?
Moving Water against Gravity
9.4
What is transpirational pull?
It is the pull caused by transpiration which results in water to move up the xylem.
What is a transpirational stream?
It is the stream of water that moves up in the plant. 56

57. Movement of water through a leaf
Moving Water against Gravity
9.4
Movement of water through a leaf
palisade mesophyll
upper epidermis with cuticle
Water that moves out of the mesophyll cells to form a thin film of moisture around the cells. 1 1
thin film of moisture 57

58. Movement of water through a leaf
Moving Water against Gravity
9.4
Movement of water through a leaf
spongy mesophyll
xylem
phloem
air spaces
Water from the thin film of moisture evaporates to form water vapour in the intercellular air spaces.
The water vapour accumulates in the air spaces near the stomata. 2 2 2 58

59. Movement of water through a leaf
Moving Water against Gravity
9.4
Movement of water through a leaf
Water vapour diffuses out of the stomata into the environment. This is evaporative cooling. 3
spongy mesophyll
lower epidermis 3 59 59

60. Movement of water through a leaf
Moving Water against Gravity
9.4
Movement of water through a leaf
Movement of water out of the cells to replace the thin film of moisture that has evaporated decreases the cell sap’s water potential. 4
xylem
phloem 6
The mesophyll cells absorb water via osmosis from the cells deeper in the leaf. 5 5 4
These cells, in turn, absorb water from the xylem vessels. 6 60

61. Movement of water through a leaf
Moving Water against Gravity
9.4
Movement of water through a leaf
This results in the production of a suction force that pulls the column of water in the xylem vessel up. 7
xylem
phloem 7 61

62. Moving Water against Gravity 9.4
Checkpoint
Outline the pathway of water from the roots to the leaves. 62

63. Pathway of water from the roots to stem
Moving Water against Gravity
9.4
Answer:
Pathway of water from the roots to stem 1
The sap in the root hair cell has lower water potential than the soil solution.
Water enters the root hair via osmosis.
Xylem conducts water away. 3
section of root
Water transfer methods:
-Apoplast (Cell wall)
-Synplast (Cytoplasm)
-Vacular ( Vacuole) 2
Water flows across the root cortex, down a water potential gradient. 63

64. Pathway of water from the roots to the leaves
Moving Water against Gravity
9.4
Answer (continued):
Pathway of water from the roots to the leaves
section of leaf
phloem
xylem
water movement by osmosis
intercellular air space 4
Water evaporates from surface of mesophyll cells into the intercellular air spaces.. 5
Water vapour diffuses out of leaf through stomata 64

65. Measuring the rate of transpiration
Moving Water against Gravity
9.4
Measuring the rate of transpiration
(1)
(2) 65

66. Calculating the rate of transpiration
Moving Water against Gravity
9.4
Calculating the rate of transpiration
Rate of transpiration = Loss in mass (g) (g/h) Time taken (h)
Rate of transpiration = Loss in volume (cm3) (cm3/h) Time taken (h) 66

67. Moving Water against Gravity 9.4
Factors affecting transpiration rate
Factor
Condition
Transpiration rate
Humidity of air
Wind or air movement
Temperature of air
Light intensity
High
Decreases
Faster
Increases
High
Increases
High
Increases 67

68. Importance of transpiration
Moving Water against Gravity
9.4
Importance of transpiration
Transpirational pall is a major suction force for moving water and mineral salts up the xylem.
Water is required at the leaves for photsynthesis.
Turgidity is maintained as water that is lost in the aerial portions of the plant is replaced.
Evaporative cooling helps to cool the plant. 68

69. Excessive transpiration
Moving Water against Gravity
9.4
Excessive transpiration
When rate of water loss exceeds rate of water absorption, wilting occurs.
What are the advantages and disadvantages of wilting? 69

70. Moving Water against Gravity 9.4
Advantages of wilting
Reduces rate of transpiration
Prevents excessive water loss
Cooling of plant
Disadvantages of wilting
Stomata close, decreasing intake of CO2 and rate of photosynthesis decreases.
Leaves droop and hence decrease absorption of sunlight, hence rate of photosynthesis decreases. 70

71. Chapter 9
Transport in Plants

72. Chapter 9 Transport in Plants
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