Exchaing Substances Part 3- Mass Transport In Plants

Question 1

What is transpiration

Answer 1

Process in which water is lost from the plant
Water evaporates form the surface of the mesophyll cell walls into the stomatal airspace
Water vapour diffuses out of the leaf through the stomata into the surrounding air

Question 2

What is the structure of xylem

Answer 2

Dead, hollow cells
No end walls
Allow water to flow from one cell to the next
One continuous tube with xylem cells stacked on top of each other
No organelles/ cytoplasm - more space for transporting water

Lignin - strengthens. Doesn’t collapse under the transpiration pull
Lignin spirals- flexibility

Pits- move in and out

Question 3

Describe the cohesion- tension theory

Answer 3

Water is lost from the leaf because of transpiration/ diffusion form mesophyll cells
This lowers water of mesophyll cells
Water pulled up the xylem - creating tension
Water molecules cohere together (by hydrogen bonds)
Forming continuous water columns
Adhesion of water molecules to walls of xylem

Question 4

What is the evidence to support the cohesion- tension theory

Answer 4

Change in diameter of tree trunks. During the day - the tree shrink sin diameter (more tension in xylem)

If xylem vessel is broken/ ai renters - tree can no longer draw up water (continuous column of water is broken, h20 molecules can no longer stick together)

Xylem vessel is broken- ate doesn’t leak out, instead air is drawn in

Question 5

What does transpiration provide

Answer 5

Water for photosynthesis

Water to maintain turgidity in cells

Movement of mineral ion from the roots to leaves

Evaporation has a cooling affect on leafs to prevent enzymes denaturing

Question 6

What factors affect transpiration and why

Answer 6

Increase temp- increase kinetic - more water rmoelces evaporate into leaf air space
Water potential gradient increases
Decrease humid y - increases water potential gradient
Increase air rmvometn
Increase light intensity

Question 7

Why might the measurement of transpiration not be accurate

Answer 7

Water used for :
Turgidity
Photosynthesis
Water produced in respiration
Apparatus not sealed/ leaks

Question 8

Describe how a potometer may be used to measure the rate of transpiration

Answer 8

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