6.4 Gas exchange in the leaf of a plant

Question 1

What reduces gas exchange with the external air in plants?

Answer 1

Plants undergo photosynthesis which means plant cells take in carbon dioxide and produce oxygen. The gases produced in one process can be used for the other

Question 2

What maintains the diffusion gradient in leaves?

Answer 2

The diffusion gradients in and out of the leaf are maintained by mitochondria carrying out respiration and chloroplasts carrying out photosynthesis.

Question 3

Describe the structure of a plant leaf

Answer 3

1. many small pores (stomata) 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 4

Give 2 points that make exchange in insects and plants similar

Answer 4

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 5

Describe the structure and function of stomata

Answer 5

• each stoma is surrounded by a pair of guard cells
• these cells can open and close on the stomatal pore
• in this way they can control the rate of gaseous exchange
• this is important as terrestrial organisms lose water by evaporation
• by closing the stomata at times when water loss would be excessive they control water loss and balance needs of gas exchange