Water transport

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

• water moves through the cytoplasm
• 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

The transpiration stream

Question 8

Explain how water moves up through the xylem, against gravity

Answer 8

• transpiration (water evaporating from the leaves) creates a tension, which pulls more water into the leaf
• water molecules are cohesive and stick together so whole columns of water in the xylem moves upwards
• water molecules also bind to the walls of the xylem through adhesive forces, helping it to rise up through the xylem

Question 9

Where and how does water exit the plant

Answer 9

Through the leaves surface called transpiration

Question 10

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

Answer 10

• 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