6.4 Gas Exchange in the leaf of a plant

Question 1

Where do cells get carbon dioxide for photosynthesis?

Answer 1

Some from respiration, but mostly from the external air. Carbon dioxide from respiration diffuses out of the cell when photosynthesis does not occur (no light)

Question 2

Where do cells obtain oxygen for photosynthesis from?

Answer 2

Most diffuses into the leaf, however some is from photosynthesis

Question 3

How is gas exchange in a plant similar to that of an insect?

Answer 3

1. No living cell is far from the external air, and therefore oxygen and carbon dioxide
2. Diffusion takes place in the gas phase (air) making it more rapid than if it were in water

Question 4

How are leaves adapted for rapid diffusion?

Answer 4

1. Many small pores, stomata, so no cell is far from one. This creates a short diffusion pathway
2. Numerous interconnecting air spaces throughout mesophyll so gases can readily come in contact with cells
3. large SA of mesophyll cells for rapid diffusion

Question 5

Where are stomata found?

Answer 5

Stomata are minute pores that occur mainly on the underside of leaves

Question 6

What controls the rate of gas exchange in stomata?

Answer 6

Each stoma is surrounded by a pair of guard cells which can open and close the stomatal pore

Question 7

How have plants evolved to control water loss?

Answer 7

Plants have evolved to balance the conflicting needs of gas exchange and water loos by closing stomata at times when water loss would be excessive