Gas Exchange In Plants

Question 1

What are dicotyledonous plants?

Answer 1

A group of flowering plants.

Question 2

Explain how the leaves of dicotyledonous plants are adapted for gas exchange.

Answer 2

1. They have many stomata, which increases the surface area for gas exchange.
2. They have a spongy mesophyll, which contains air spaces; this increases the surface area for gas exchange.
3. They are thin which provides a short diffusion pathway.

Question 3

Explain the structural adaptation in xerophytic cells that allows efficient gas exchange and limits water loss?

Answer 3

1. They have a thicker waxy cuticle, which increases the diffusion distance and limits the amount of evaporation.
2. They have sunken stomata in pits. These trap water, reduce the water potential gradient and limit the amount of evaporation.
3. They have spines which reduce the surface area: volume ratio.

Question 4

How do guard cells control the opening and closing of the gard cells?

Answer 4

1. When the water potential outside the guard cells is higher compared to inside the guard cells, water moves into the guard cells via osmosis.
2. This causes the guard cells to become turgid. This forces the stomata open to allow gas exchange to occur.
3. When the water potential outside the guard cells is lower compared to inside the guard, water moves out of the guard cells via osmosis.
4. This causes the guard cells to become flaccid. This forces the stomata close to limit the amount of water lost.