transport of water

Question 1

What process does water use to enter into the roots from the soil?

Answer 1

Osmosis, going from a high water potential to a low water potential

Question 2

What process do mineral ions use to enter the roots from the soil?

Answer 2

Active transport, going from a low concentration to a high concentration

Question 3

Explain how the 2 processes of osmosis and active transport is maintained

Answer 3

• the endodermis cells carry out active transport which delivers minerals from the cortex to the xylem
• this lowers the water potential in xylem, so water enters through osmosis

Question 4

What is the apoplast pathway for movement of water through the roots?

Answer 4

• Water moves through the cell walls
• the walls are very absorbent and water can simply diffuse through them.
• the water can carry solutes
• cohesive and tension forces acting on the plant is what pulls the water up the plant
• water always moves from areas of high hydrostatic pressure to areas of low hydrostatic pressure.
• example of mass flow
• fastest movement of water

Question 5

What is the symplast pathway for movement of water through the roots?

Answer 5

• What is the symplast pathway for movement of water through the roots?
• the cytoplasm of neighbouring cells connect through plasmodesmata (small channels in the cell wall)
• water moves through osmosis

Question 6

What happens to the water travelling along the apoplast pathway when it gets to the endodermis cells in the roots? Explain why this is good

Answer 6

• its path is blocked by the casparian strip (a waxy strip which is waterproof and made of Suberin), so the water has to now take the symplast pathway
• this is good because the water now has to go through a cell membrane, which are partially permeable and able to control if substances in the water get through

Question 7

What is the movement of water from the roots to the leaves called?

Answer 7

transpiration stream

Question 8

Where and how does water exit the plant

Answer 8

Through the leaves surface called transpiration

Question 9

How does water move from the xylem vessels into the leaves and then out of the plant?

Answer 9

• water moves mainly through the apoplast pathway in the leaf cells
• water then evaporates from the cell walls into the spaces between the spongy mesophyll cells
• water vapour then diffuses out of the stomata into the surrounding air

Question 10

explain why water loss from plant leaves is unavoidable (2 marks)

Answer 10

the stomata open and close to allow the exchange of gases between outside and inside of leaf. gas exchange is required for photosynthesis so water diffuses out too.

Question 11

state and explain two adaptations of leaves that reduce evaporation (2 marks)

Answer 11

• waxy cuticle = waterproof, stops water vapour escaping through epidermis
• hairy leaves = reduce air flow and increases humidity which reduces water potential gradient by trapping water vapour