Mass Transport Plants EQs

Question 1

Explain the cohesion tension theory to transport water up the xylem?

Answer 1

Water is lost from the leaf due to transpiration
This lowers the water potential of the leaf
Water is puller up the xylem by tension
Water molecules cohere by hydrogen bonding forming a Water column
Adhesion of water to the walls of the xylem

Question 2

Explain how the xylem is adapted to its function?

Answer 2

Hollow-allows for water to travel consistently
No end walls-continous transpiration and allows cohesion
Very thin tubes-high SA to V ratio more hydrogen bonds form increasing adhesion
Lignification-provides xylem with stability and strength
No organelles so less obstruction
Waterproof so resists tension

Question 3

Investigate the mass flow hypothesis?

Answer 3

In the leaf sugars are actively transported into the phloem/sieve tube cells
By companion cells
This lowers the water potential in the sieve cell so water enters by osmosis
Increase in movement causes hydrostatic pressure
Sugars are actively transported into root hair cells
Lowers water potential in root hair cells and creates a pressure gradient

Question 4

How does an increase in wind speed increase the rate of transpiration?

Answer 4

More water evaporates from the spongy mesophyll cell and diffuses through the stomata
Reduces water potential in the spongy mesophyll water pulled up the xylem
Water molecules cohere by hydrogen bonds
Forming a continous water column

Question 5

How are xerophytes adapted?

Answer 5

Sunken stomata to trap water vapour and reduce concentration gradient
Curled leaves so less evaporation as less surface area exposed to the wind
Stomata only open at night so less evaporation