Gas exchange in the leaf of a plant

Question 1

How can plants reduce the gas exchange with external air?

Answer 1

Sometimes the gases produced in one process can be used for another so it doesn’t constantly need to exchange from external air.

Question 2

How does the volume and type of gases which are being exchanged by a plant leaf change?

Answer 2

It depends on the balance between the rate of photosynthesis and respiration:

• When photosynthesis happens, some CO2 comes from the respiration of the cells but mostly comes from the external air. Similarly, some O2 are been used in respiration but mostly diffused out of the plant.
• When photosynthesis isn’t happening, e.g. in the dark, O2 diffuses into the leaf because it’s constantly been used up during respiration and CO2 is produced during respiration which then is diffused out.

Question 3

How does the structure of the plant leaf make it efficient for gas exchange?

Answer 3

• All living cells are close to the external air so it’s close to sources of O2 and CO2.
• Diffusion takes place is gaseous air, which is much more rapid than it is to be taken in water.
  (So overall a short, fast diffusion pathway).
• There are air spaces inside a leaf has a large SA in comparison to its volume of living tissue.

Question 4

How is a plant leaf adapted for rapid diffusion of gas?

Answer 4

• Many small pores, stomata which open to allow gas exchange, and close to control loss of water. The closing and openings are controlled by guard cells.
• Many air spaces throughout the mesophyll so gases can readily come in contact with mesophyll cells.
• Large SA of mesophyll cells for rapid diffusion.

Question 5

What does do stomata in a leaf?

Answer 5

• They can usually be found on the underside of the leaf. - - Each stoma is surrounded by a pair of guard cells.
• The guard cells can open and close the stomatal pore which can control the rate of gaseous exchange, this is important because plant cells can lose water by evaporation.
• So through the opening and closing of the guard cells, it can balance the needs for gas exchange and control of water loss.