INSECTS FISH PLANTS

Question 1

Adaptations for efficient gas exchange in fish

Answer 1

-Large surface to volume ratio (created by many gill filaments covered in many gill lamellae)
-Short diffusion distance (due to a capillary network in every lamellae and very thin gill lamellae)
-Maintaing conc gradient (with countercurrent flow mechanism)

Question 2

Countercurrent exchange principle

Answer 2

In the gills of fish, blood flows through the lamellae in one direction and water flows over them in the opposite direction.
The countercurrent system means that the water with a relatively high oxygen concentration always flows next to the blood with a lower concentration of oxygen. Ensuring equilibrium not reached. This ensures a steep concentration gradient is maintained across the entire length of the lamellae

Question 3

Control of water loss in xerophytes.

Answer 3

-Stomata sunk in pits to trap water vapour, reducing the concentration gradient of water between the leaf and the air. This reduces evaporation of water from the leaf
-A layer of ‘hairs’ on the epidermis to trap water vapour round the stomata
-Curled leaves with the stomata inside, protecting them from wind(windy conditions increase rate of diffusion and evaporation)
-A reduced number of stomata, so there are fewer places for water to escape
-Thicker waxy waterproof cuticles on leaves and stems to reduce evaporation.