1. Transport system in plants Movement of water through a Plant
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KNOWLEDGE AREA: Life processes in plants and animals
Topic : Support and transport systems in plants
Transport system in plants Movement of water through a Plant

2. SUMMARY OF THE PRESENTATION
Transpiration and Guttation.
Wilting
Absorption and Transport of Water and Mineral Salts.
Lateral Transport of Water and Mineral Salts to the Stele.
Upward Movement of Water and Mineral Salts in a Plant.
Translocation of Manufactured foods from Leaves to the rest of the Plant.

3. transpiration
Transpiration is the process during which water is lost in the form of water vapour from the aerial parts of the plant, mainly through the stomata of the leaves.
Transpiration has both advantages and disadvantages.
We will concentrate on the advantages and look at the disadvantages later.

4. transpiration

5. transpiration ADVANTAGES OF TRANSPIRATION:
Transpiration leads to transpiration pull, which in turn is responsible for the upward movement of water through the plant.
Transpiration helps in the cooling of the plant through the loss of water vapour.

6. transpiration RELATIONSHIP BETWEEN WATER LOSS AND LEAF STRUCTURE:
We must remember that leaves are all not the same.
They differ in the following ways::
Their shape and size.
The arrangement of the leaves themselves.
Hairs: are present or not.
The cuticle: thickness.
The stomata: number and position

7. transpiration
These differences effect the rate at which water is lost form the plant , through transpiration.
The rate at which water is lost through transpiration is called the rate of transpiration.
The rate of transpiration refers to how quickly or slowly water vapour is lost from the plant.

8. transpiration
They can change the rate of transpiration in the following ways:
The shape and size of leaves are changed to reduce the surface area and this leads to a reduction in the rate of transpiration. Example the leaves of the pine tree which are needle- shaped.
Leaves may overlap each other to reduce surface area exposed to the sun and therefore reduces the rate of transpiration.

9. transpiration
Hairs maybe present on some leaves, these hairs reflect sunlight and reduces air movement, therefore reducing the rate of transpiration.
Waterproof cuticle maybe thickened to further reduce the rate of transpiration.
The arrangement and number of stomata may be altered to reduce the rate of transpiration. For example more stomata are found on the undersurface of the leaf, away from the direct sunlight. Some of the stomata are sunken to trap moisture reducing the rate of transpiration.

10. transpiration
Effect of Environmental factors on the rate of Transpiration:
Earlier we discussed how the structure of the leaf affected the rate of transpiration. We call these internal structures.
The environment may also affect the rate of transpiration. These are called external factors.
We shall now discuss how these external factors affect the rate of transpiration.

11. transpiration
Wind:
Usually there is a pocket of humid air around the leaf.
The wind blows away the pocket of humid air.
Therefore there is a higher concentration of water vapour molecules inside the leaf than outside.
Remember that water always moves from a region of high concentration to a region of lower concentration. ( In other words from where there is a lot to where there is a little.)

12. transpiration
Therefore water would move out of the leaf into the surrounding atmosphere.
Therefore wind increases the rate of transpiration.
However very strong winds causes the stomata to close, reducing the rate of transpiration.

13. transpiration Temperature:
When the temperature increases the kinetic energy of the water molecules also increases.
This increased energy causes the water molecules to move faster. In other words they move at a faster rate.
Therefore more water molecules will diffuse out of the leaf on a hot.
In other words the rate of diffusion of water molecules out of the leaf is higher on a hot day than a cold one.
This means that…

14. transpiration
high temperatures increases the rate of transpiration.

15. transpiration
Humidity:
Humidity refers to the amount of moisture in the atmosphere.
On a humid day there is a high concentration of water vapour around the leaves.
Therefore water will remain within the leaf because there is a higher concentration of water vapour molecules outside the leaves.
Remember that water moves from a region of high concentration to a region of low concentration.
This means that…

16. transpiration
increased humidity decreases the rate of transpiration.

17. transpiration Light Intensity:
The stomata open in the presence of light.
Therefore as light intensity increases the rate of transpiration…
increases.
However if the light intensity is too high the stomata closes to prevent excessive loss of water.

18. Guttation:
Guttation is the loss of water in the form of droplets form special pores in the leaves called hydathodes.
The hydathodes are found on the margins of the leaves.
It occurs in the following way…
Guttation

19. Guttation:
If the air is very humid transpiration may slow down or can even stop because there is more moisture outside the leaf that in.
The concentration gradient has been reversed.
If there is enough moisture in the soil and the plant has absorbed more water than necessary then it loses the excess water in the form of droplets through the hydathodes.

20. wilting
Sometimes the environmental factors causes an increase in transpiration, causing the plant to lose a large amount of water.
The plant must be able to absorb more water from the soil to replace the water lost through transpiration.
If the soil does not have enough water or the roots do not have a large enough surface area to absorb enough water to replace the lost water then..
The xylem absorbs the water from the surrounding cells for example the parenchyma.

21. wilting The loss of water causes… the vacuoles to shrink in size and
Sometimes even the volume of the cytoplasm to decrease due to the water loss.
These cells lose the tugour or turgidity.
This loss of turgidity can sometimes result in the leaves and even stems becoming limp.
They then droop.
When this happens then the plant is wilting.

22. wilting
However wilting does not have to be permanent, it can be reversed if the plant is placed in water or water is added to the soil, provided that it did not suffer a water loss for too long.

23. Absorption and transport of water & mineral salts by plants:
The root hair is responsible for the absorption of water and mineral salts from the soil.
This is possible because the soil water always has a higher concentration of water molecules than the cell sap of the vacuole in the root hair.
The cell sap has a lower concentration of water because it has a high concentration of salts.
This difference in concentration ensures that water will always move into the root.
The water moves into the root by osmosis.

24. Absorption and transport of water & mineral salts by plants:
Remember that osmosis is the movement of water from a region of high concentration to a region of low water concentration across a differentially permeable membrane until equilibrium is reached.
The cell membrane and tonoplast of the vacuole act as a differentially permeable membranes.
Therefore water simply moves into the root by osmosis.

25. Absorption and transport of water & mineral salts by plants:
However with the absorption of mineral salts it is slightly different.
Mineral salts cannot diffuse into the root because there is a higher concentration of salts in the vacuole than in the soil water.
This means that mineral salts have to be absorbed from a region of low concentration to a region of high concentration.
When this happens we say that the substance is being absorbed against the concentration gradient.
This process is called active transport because it requires energy.

26. Lateral transport of water to the stele:
Remember the soil has a higher concentration of water molecules than the cell sap of the vacuole therefore water will move into the epidermis of the root by osmosis.
Now the epidermis has a higher water concentration that the cells of the cortex.
Diagram showing the lateral
movement of water through
the root.

27. Lateral transport of water to the stele:
Therefore water will now enter the cells of the cortex through osmosis.
This entry of water now ensures that the cells of the cortex has a higher water concentration than the endodermal cells.
Water would therefore move into the endodermal cell by osmosis.
The endodermal cells directs the movement of water because some of the cells are thickened by the casparian strip. The water is only able to move through the non thickened passage cells.
The endodermal cells now have a higher water concentration than the cells of the xylem.
Water will therefore enter the xylem by osmosis.

28. Something for you to do:
Explain the lateral movement of water in the root using the diagram below.

29. Solution:
Since the soil water has a higher water concentration than the epidermis of the root, water enters the epidermis of the root by osmosis.
The epidermis now has a higher water concentration than the parenchyma cells of the cortex.
Water will therefore move into the parenchyma cells of the cortex by osmosis.
The parenchyma cells of the cortex now has a higher water concentration than the cells of the endodermis.

30. Solution:
The endodermis directs the follow of water by allowing the water to move only through the passage cells to the cells of the xylem.
The passage cells are unthickened, while the rest of the endodermis is thickened by the casparian strip.
Water therefore enters the xylem by osmosis, because the endodermis has a higher water concentration than the xylem.

31. Upward movement of water & mineral salts through the plant
Water moves up the plant by 3 processes.
These are:
Root pressure
Capillarity
Transpiration pull
Root Pressure:
This process forces water up the xylem for only a short distance.
It is an upward force that is brought about by the continuous entry of water into the roots.

32. Upward movement of water & mineral salts through the plant
Capillarity:
Capillarity is the natural tendency of liquid to move up tubes with fine bores on their own.
A fine bore means that the tube has a very small diameter.
Xylem vessels and tracheids are very long tubes with fine bores.
Therefore water will move up xylem vessels and tracheids by capillarity.
However capillarity is only responsible for the movement of water only very short distances.

33. Upward movement of water & mineral salts through the plant
Transpiration Pull:
This is the main force responsible for pulling water up the xylem of a plant.
It occurs in the following way:
When transpiration occurs, the water is evaporated from the air space of the sub- stomatal chamber.
The air space now has a lower concentration of water molecules than the mesophyll cells.
Therefore water from the mesophyll cells now enter the air space of the sub-stomatal chamber.

34. Upward movement of water & mineral salts through the plant
Now the concentration of water molecules of the mesophyll tissue is lower than the concentration of water molecules in the xylem of the leaf.
Therefore water moves from the xylem to the mesophyll tissue.
But the xylem of the leaf is continuous with the xylem of the stem and the xylem of the root.
And strong forces of attraction exist between water molecules themselves. This force is called the cohesive force.

35. Upward movement of water & mineral salts through the plant
Therefore when water moves from the xylem of the leaf into the mesophyll tissue, the tension is transmitted into the xylem of the stem and root.
Therefore water will move be pulled up the plant as a column of water.
The cohesive force between the water molecules and continuation of the xylem of the root, stems and leaves ensure that water moves up the plant as a column of water.

36. Translocation of manufactured food from leaves to other parts of the plant
Unfortunately the transport of manufactured food through the plant is still under investigation by scientists and not fully understood yet.
However here is what is understood:
Manufactured food is transported by the sieve tube of the phloem.
This food (in the form of glucose) is transported as cytoplasmic strands.
The cytoplasmic strands pass from one sieve tube to another through the sieve plates.

37. Terminology:
Transpiration: is the process during which water is lost in the form of water vapour from the aerial parts of the plant, mainly through the stomata of the leaves.
Rate of transpiration: refers to how quickly or slowly water vapour is lost from the plant
Humidity: refers to the moisture in the atmosphere.
Guttation: is the loss of water in the form of droplets from the hydathodes of the leaves.

38. Terminology:
Hydathodes: these are pores found on the leaf margin through which guttation occurs.
Wilting: when the leaves and stems droop as a result of water loss from the vacuole of cells.
Active transport: when substances are absorbed against a concentration gradient and energy is required for this process.
Cohesive forces: are the forces of attraction between water molecules themselves.
Root pressure: is the upward force caused by the continual entry of water into the roots.
Capillarity: is the natural tendency of liquids to move up tubes with fine bores.

39. The force necessary for the upward movement of water is called…
A. Root pressure
B. Capillarity
C. Transpiration pull
D. Xylem pressure
QUESTION 1

40. QUESTION 2
The natural tendency for liquids to move up tubes with fine bores is called…
A. Root pressure
B. Capillarity
C. Transpiration pull
D. Xylem pressure

41. The upward force that is caused by the continual entry of water into the roots is called…
A. Root pressure
B. Capillarity
C. Transpiration pull
D. Xylem pressure
QUESTION 3

42. Water is able to move up the plant as a continuous column because of the…
A. Cohesive forces of water molecules only
B. Continuation of the xylem of the leaf with the xylem of the root and stem.
C. Root pressure.
D. Both A and B
QUESTION 4

43. QUESTION 5 Water enters the epidermis of the root because…
A. The soil water has a higher water molecule concentration
B. The epidermis has a higher water molecule concentration
C. The soil water has a lower water molecule concentration
D. Both A and B
QUESTION 5

44. The endodermis is able to direct the flow of water because of its…
A. Completely thickened walls of the cells
B. Passage cells that are also thickened
C. Unthickened passage cells
D. None of the above
QUESTION 6

45. QUESTION 7 Mineral salts are absorbed by active transport because…
A. They are absorbed against the concentration gradient
B. Energy is required for their absorption
C. They are absorbed with the concentration gradient
D. Both A and B
QUESTION 7

46. Mineral salts cannot enter the root hairs by diffusion because…
A. The cell sap already has a high salt content
B. The cell sap has a lower salt content
C. The soil has a high salt concentration
D. There is no mineral salt in the soil
QUESTION 8

47. QUESTION 9 Water enters the root hairs by the process of… A. Diffusion
B. Root pressure
C. Osmosis
D. Streaming
QUESTION 9

48. The process during which water is lost in the form of droplets form the hydathodes of the leaves is called…
A. Transpiration
B. Guttation
C. Wilting
D. osmosis
QUESTION 10

49. The process during which the plant loses water in the form of water vapour through the aerial parts of the plant is called…
A. Transpiration
B. Guttation
C. Wilting
D. osmosis
QUESTION 11

50. When the leaves and even stems droop because the plant cell became flaccid is called…
A. Transpiration
B. Guttation
C. Wilting
D. Osmosis
QUESTION 12

51. QUESTION 13 Wilting occurs because the…
A. Cell have taken in excess water and the vacuole becomes swollen.
B. The vacuoles lose water because the plant cannot replace the large amount of water lost through transpiration
C. Water enters the root continuously
D. Water moves up the xylem
QUESTION 13

52. QUESTION 14 Rate of transpiration in increases when…
A. Temperature increases
B. Humidity increases
C. Light intensity decreases
D. Temperature decreases

53. QUESTION 15 Rate of transpiration decreases when…
A. Humidity increases and temperature decreases
B. Humidity decreases and temperature increases.
C. When humidity and temperature decreases
D. When humidity and temperature increases
QUESTION 15

54. QUESTION 16 Light intensity increases rate of transpiration because…
A. The stomata opens in the presence of light
B. Stomata closes in the presence of light
C. The water molecules have less energy
D. None of the above
QUESTION 16

55. QUESTION 17 The rate of transpiration is reduced if a plant has…
A. More stomata on its upper surface
B. No cuticle
C. A large surface area
D. None of the above
QUESTION 17

56. QUESTION 18
Hairs on leaves are able to reduce water loss through transpiration because…
A. The hairs reflect light
B. The hairs reduce air movement
C. Both A and B
D. None of the above

57. A plant that has_____________ will have a reduced rate of transpiration.
A. Hairs on leaves and is broad and flat
B. Hairs on the leaves and is thin and narrow
C. Hairs on the leaves and a large number of stomata on its upper surface
D. Hairs on its leaves and no cuticle
QUESTION 19

58. QUESTION 20 Sunken stomata reduce water loss by transpiration because…
A. Water vapour collects in the sunken pockets.
B. The air in the sunken pockets is dry
C. There is a higher concentration of water molecules inside the leaf
D. None of the above

59. SOLUTION: C B A D A C B D