water transport

Question 1

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

Answer 1

osmosis
- from high to low water potential

Question 2

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

Answer 2

active transport
- from low to high concentration

Question 3

explain how osmosis and active transport are maintained

Answer 3

• endodermal cells carry out AT - delivers minerals from cortex to xylem
• this lowers water potential in xylem so water enters through osmosis

Question 4

describe the apoplast pathway for movement of water through the roots

Answer 4

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

Question 5

describe the symplast pathway for movement of water through the roots

Answer 5

• cytoplasm of neighbouring cells connect through plasmodesmata (small channels in the cell wall)
• water moves through osmosis

Question 6

which pathway is the fastest?

Answer 6

apoplast

Question 7

what happens to water travelling along the apoplast pathway when it gets to the endodermis cells in the roots?

Answer 7

path is blocked by casparian strip (a waxy, waterproof strip made of Suberin), so water has to move into the cell and continue through symplast pathway

Question 8

why is it good that water must move from the apoplast pathway into the symplast pathway?

Answer 8

water has to go through a partially permeable cell membrane - able to control if substances in the water get through (eg. toxins)

Question 9

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

Answer 9

transpiration stream

Question 10

where and how does water exit the plant?

Answer 10

through the leaves surface - through stomata

Question 11

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

Answer 11

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

Question 12

why is water loss from plant leaves unavoidable?

Answer 12

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

Question 13

state and explain two adaptations of leaves that reduce evaporation

Answer 13

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