Gas Exchange: Plants

Question 1

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

Answer 1

1. Many stomata (high density) → large surface area for gas exchange (when opened by guard cells)
2. Spongy mesophyll contains air spaces → large surface area for gases to diffuse through
3. Thin → short diffusion distance

Question 2

Xerophyte:

Answer 2

Plant adapted to live in very dry conditions eg. Cacti and marram grass.

Question 3

Explain structural and functional compromises in xerophytic plants that allow efficient gas exchange while limiting water loss:

Answer 3

1. Thicker waxy cuticle
   ○ Increases diffusion distance so less evaporation
2. Sunken stomata in pits / rolled leaves / hairs
   ○ ‘Trap’ water vapour / protect stomata from wind
   ○ So reduced water potential gradient between leaf / air
   ○ So less evaporation
3. Spines / needles
   ○ Reduces surface area to volume ratio