1. Chapter : Transport in Plants
state the functions of xylem and phloem.
identify the positions of xylem and phloem tissues as seen in transverse section of roots, stems and leaves.
investigate, using a suitable stain, the pathway of water in a cut stem.

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

3. Think Like a Scientist
Scientists use ‘thought experiments’ to help them solve problems. 3

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

5. How does water move through the transport system of a plant IF
it does not have a heart to act as a pump?
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 from the leaves to the roots?
PAUSE to
PONDER 5

6. 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?

7. Transport in Plants
Plants need a transport system so that cells deep within the plants tissues can receive the nutrients they need for cell processes
The problem in plants is that roots can obtain water, but not sugar, and leaves can produce sugar, but can’t get water from the air

8. What substances need to be moved?
The transport system in plants is called vascular tissue
Xylem tissue transports water and soluble minerals
Phloem tissue transports sugars

9. Structure of Xylem
Used to transport water and minerals from roots to leaves
Consists of tubes for water, fibres for support and living parenchyma cells

10. Xylem vessels Obvious in dicotyledonous plants
Long cells with thick walls containing lignin
Lignin waterproofs walls of cells and strengthens them
Cells die and ends decay forming a long tube
Lignin forms spiral, annular rings or broken rings (reticulate)
Some lignification is not complete and pores are left called pits or bordered pits, allowing water to move between vessels or into living parts

12. Adaptations of Xylem to Function
Xylem can carry water and minerals from roots to shoot tips because:
Made of dead cells forming continuous column
Tubes are narrow so capillary action is effective
Pits allow water to move sideways
Lignin is strong and allows for stretching
Flow of water is not impeded as: there are no end walls, no cell contents, no nucleus, lignin prevents tubes collapsing

14. Structure of Phloem
Function to transport sugars from one part to another
Made of sieve tube elements and companion cells

15. Sieve Tubes
Sieve tube elements not true cells as they have little cytoplasm
Lined up end to end to form a tube
Sucrose is dissolved in water to form a sap
Tubes (known as sieve tubes) have a few walls across the lumen of the tube with pores (sieve plates)

17. Companion cells In between sieve tubes Large nucleus, dense cytoplasm
Many mitochondria to load sucrose into sieve tubes
Many gaps in cell walls between companion cells and sieve tubes for flow of minerals

19. The Vascular Tissues
Xylem and phloem are found together in vascular bundles, that sometimes contain other tissues that support and strengthen them

20. Vascular bundles: xylem & phloem
Xylem transports water & dissolved minerals from roots to leaves.
Phloem transports food (sugar) made in leaves to all other parts of the plant.

21. Stem The vascular bundles are found near the outer edge of the stem
The xylem is found towards the inside of each vascular bundle, the phloem is found towards the outside
In between the xylem and phloem is a layer of cambium
Cambium is a layer of meristem cells that divide to make new xylem and phloem

22. Xylem & phloem tissues in stems.

23. Phloem
Xylem
Stem

24. Root The vascular bundle is found in the centre
There is a large central core of xylem- often in an x-shape
This arrangement provides strength to withstand the pulling forces to which roots are exposed
Around the vascular bundle are cells called the endodermis which help to get water into the xylem vessels
Just inside the endodermis is the periycle which contains meristem cells that can divide (for growth)

25. Distribution of vascular bundles in roots
xylem
phloem
Distribution of vascular bundles in roots
xylem
phloem

26. Xylem vessel wall
Xylem vessel lumen
Phloem
Endodermis
Starch grains
Root

27. Leaf
The vascular bundles (xylem and phloem) form the midrib and veins of the leaf
A dicotyledon leaf has a branching network of veins that get smaller as they branch away from the midrib
Within each vein, the xylem can be seen on top of the phloem

28. Distribution of vascular bundles in leaves.
xylem
phloem
Distribution of vascular bundles in leaves.

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

30. C/D = Upper/Lower epidermis
A = Xylem
B = Phloem
C/D = Upper/Lower epidermis
Leaf

31. Root vs. stem vs. leaf
The vascular bundle differs depending on if it is a root or stem

32. Transport Structures Leaf Stem Root Xylem Phloem Xylem Xylem Phloem

33. Chapter : Transport in Flowering Plants
describe the structure and functions of root hair cells in relation to their surface area, and to water and ion uptake.
define transpiration.
describe how factors (e.g humidity, temperature, light intensity) affect the rate of transpiration.
describe how wilting occurs.

34. Transport of Water

35. Root
Stem
Leaves

36. Water uptake in ROOT
Animation

37. How does the root maintain a concentration gradient?
Root Pressure
Osmotic pressure that build up within the root cells which forces water up the root xylem
Recap on Osmosis
How does the root maintain a concentration gradient?

38. Root Pressure Uptake of water by the root hair by Osmosis
Uptake of dissolved minerals through active transport
Cell sap within the root hairs becomes more concentrated than the water in the soil

39. Root Pressure
Occurs when the soil moisture level is high either at night or when transpiration is low during the day
Can only raise the water in some plants up to 20cm
Not the main force

41. Water transport in STEM
You have learnt that water is transported from the root to the stem and the leaf.
How does the plant transport water upwards against gravity??

42. Transpiration Evaporation of water from the plant
Loss of water vapor through the stomata on the underside of the leaves
The mesophyll cells in the leaves are covered with a thin layer of moisture
Essential for efficient gas exchange to occur
Some of this moisture evaporates into the intercellular spaces which diffuses through the stomata into the ‘drier’ air
Water is pulled upwards through osmosis (Transpiration Pull)
The waterway in which the water moves from a higher water potential to a lower water potential
Transpiration Stream

43. 4 Environmental Factors that affect Transpiration
Animation
Wind speed
Humidity
Light intensity
Temperature
Water supply

44. Light intensity During the day, stomata of the leaves open. Why?
Photosynthesis!!
Gases exchange (CO2 & O2)
Water vapor also evaporates (Transpiration)

45. At 30ºC, a leaf may transpire 3 times as fast as it does at 20ºC
Temperature
The higher the temperature, the higher the air water capacity to hold moisture
At 30ºC, a leaf may transpire 3 times as fast as it does at 20ºC

46. 5 Factors that affect Transpiration
Wind speed
Increases  Increases transpiration rate
Humidity
Increases  Decreases transpiration rate
Light intensity
Temperature
Water supply
Decreases  Decreases transpiration rate

47. Potometer
The rate at which plants take up water depends on the rate of transpiration- the faster a plant transpires, the faster it takes up water.

48. Capillary Action
The attractive force between the molecules of a particular liquid is known as Cohesion
Water coheres to each other via chemical bonds called hydrogen bonds (holds the droplets of water together)
The attractive force between two unlike materials is known as Adhesion
Adhesion causes water to stick to the inside of the glass
When water passes up the thin xylem vessels, it adheres to the surface of the vessels, while the force of osmosis gently ‘pushes’ the water molecules, which cohere to each other, upwards

50. Capillary Action

51. Forces that promotes uptake of water
Root Pressure
Promotes uptake of water in the root
Transpiration pull
Main force to ‘suck’ up the water
Capillary Action
Pushes the water upwards due to the adhesion between the walls of the xylem vessels and water molecules as well as the cohesion between the water molecules

52. Transport of Food

53. Transport of Food in plant
Food substances (sugar & amino acids) are manufactured in the green leaves through the process called photosynthesis
Translocation is the process of transporting food substances downwards from the leaves to all other parts of the plant, through the phloem

54. Animation
Animation

55. How would you show phloem transports food substances?

56. 3 experiments to show phloem transport food substances
Using Aphids
Aphid penetrates the stem into the phloem using its mouthpart called stylet and sucks the plant sap
A feeding aphid can be anaesthetized and the stylet cut off
The phloem sap flows out through the stylet and can be analysed. It is found to contain sugars and other organic substances

58. 3 experiments to show phloem transport food substances
The Ringing Experiment
Swelling above the ring
Reduced growth below the ring
Leaves are unaffected

59. 3 experiments to show phloem transport food substances
Using radio-isotopes

60. Wilting of plant

61. Wilt
Temporary or permanent loss of turgor pressure due to excessive transpiration of the leaves & shoot
Result in flaccid appearances of leaves & shoot
Characterized by drooping & shriveling of soft tissue

62. Is wilting necessary a disadvantage to the plants? Why?
b.      Wilting reduces loss of water in leaves. How does it affect intake of water for photosynthesis?
c.       How is it the prolong process of wilting cause harm to plants?
d.      What other conditions may cause plants to wilt?

63. Advantage of wilting
Rate of transpiration reduces as the leaves folds up, reducing surface that is exposed to sunlight.
This will cause guard cells to become flaccid and the stomata will close to conserve water in the plant.
Disadvantage of wilting
Rate of photosynthesis will be reduced due to the following reasons:
Water becomes a limiting factor now.
The amount of sunlight that can be absorbed becomes a limiting factor as leaves shriveled up.
The amount of carbon dioxide becomes a limiting factor as the stomata are closed.

64. Things to ponder What time of the day should you water your plant?
Too much water, is it good for your plant?

65. People often give potted houseplants more fertilizer than they need
People often give potted houseplants more fertilizer than they need. As a result, the plants begin to wilt and eventually die instead of getting larger and healthier. What could be the reason for this result?

66. “Girdling” or ring-barking is a term referring to the bark of the tree in a complete ring around the trunk or a branch. Predict the effect that girdling will have on a tree. Explain. Beneficial or Destructive to plants?