6.4 Gas exchange in the leaf of a plant

Question 1

What happens when photosynthesis is taking place in terms of gases

Answer 1

Some carbon dioxide comes from respiration of cells, most of it is obtained from the external air however

In the same way, some oxygen from photosynthesis is used in respiration but most of it diffuses out of the plant

Question 2

What happens when photosynthesis is not occurring

Answer 2

Oxygen diffuses into the leaf because it is constantly being used by cells during respiration. In the same way, carbon dioxide produced during respiration diffuses out

Question 3

How is gas exchange in plants similar to that of insects

Answer 3

1. No living cell is far from the external air, and therefore a source of oxygen and carbon dioxide
2. Diffusion takes place in the gas phase, which makes it more rapid than if it were in water

Question 4

Where does most gas exchange occur

Answer 4

In the leaves

Question 5

What adaptations do leaves have for rapid diffusion

Answer 5

1. Many small pores, called stomata, and so no cell is far from a stoma and therefore the diffusion pathway is short
2. numerous interconnecting air-spaces that occur throughout the mesophyll so that gases can readily come in contact with mesophyll cells
3. Large surface area of mesophyll cells for rapid diffusion

Question 6

What are stomata

Answer 6

Small minute pores that occur mainly on the leaves, especially the underside

Question 7

What are each stoma surrounded by

Answer 7

Guard cells which open and close the stomatal pore

Question 8

Why is the opening and closing of stoma by guard cells important

Answer 8

Because terrestrial organisms lose water by evaporation. Plants have evolved to balance the conflicting needs of gas exchange and control of water loss