Mass Transport in Plants

Question 1

What are the 3 paths of water uptake in the roots

Answer 1

1 - Vacuolar
2- Symplast
3- Apoplast

Question 2

Describe the cohesion-tension theory of water transport in the Xylem

Answer 2

1 - Water lost from leaf due to transpiration
2 - Lowers water potential in leaf cells
3 - Water pulled up through Xylem (creating tension)
4 - Water molecules cohere (due to Hydrogen bonds)
5 - Forming continuous water column
6 - Adhesion of water molecules to walls of Xylem

Question 3

Why are xylem cells ‘dead’

Answer 3

Walls are lignified
Lignin is impermeable
Prevents substances from passing through cell wall
Living contents of cells die.

Question 4

How does lignin support xylem vessels?

Answer 4

When water is pulled up xylem vessels, causes pressure in vessels to fall
Lignin prevents vessels from collapsing

Question 5

How does a thicker waxy cuticle help Xerophytes?

Answer 5

Thicker Waxy Cuticle - Increases diffusion distance so less evaporation

Question 6

How does sunken stomata in pits/rolled leaves/hairs help Xerophytes?

Answer 6

• Traps water vapour & protects stomata from wind
• Reduces water potential gradient between leaf and air
• So less evaporation

Question 7

How do spines & needles help Xerophytes?

Answer 7

They reduce the SA:V ratio

Question 8

How do hinge cells help xerophytes?

Answer 8

When flaccid, they cause leaves to roll, creating a humid space