Gas exchange in animals and plantsEdexcel A-Level Biology B: Mind map

Exam questions on Gas exchange in animals and plants

1. A locust is an insect that can fly long distances. Air enters its body through paired openings along the thorax and abdomen. From these openings a branching network of air-filled tubes carries air towards the tissues, and the finest tubes end in thin-walled, fluid-filled tips lying against the flight muscle cells. The locust has no oxygen-carrying pigment in its body fluid.
   Explain how the structure of the tracheal system allows the flight muscle cells to be supplied with oxygen rapidly.2 marks
2. Trout live in cold, fast-flowing streams, where the water contains far less oxygen than air does. A trout takes water in through its mouth and passes it over its gills before it leaves beneath a bony flap. Each gill has many filaments, and each filament bears many thin plate-like lamellae containing blood capillaries. Blood flows through each lamella in the opposite direction to the water. Blood leaving a lamella of a trout is about 80% saturated with oxygen, whereas if blood and water flowed in the same direction the blood could not exceed about 50% saturation.
   Explain why the counter-current flow of blood and water in the lamellae allows the trout to take up more oxygen than parallel flow would.2 marks
3. Marram grass grows on exposed sand dunes, where it is windy, hot and dry. In dry weather its leaves roll up into a tube. Its stomata are found only on the inner surface of the leaf, where they sit in pits lined with hairs, and the outer surface of the leaf is covered by a thick waxy cuticle.
   Explain how these features of marram grass reduce the loss of water.3 marks