Gas exchange in single-celled organisms, insects and fishAQA A-Level Biology: Mind map

Exam questions on Gas exchange in single-celled organisms, insects and fish

1. Amoeba is a single-celled organism that lives in freshwater ponds. It takes in oxygen and loses carbon dioxide across its cell surface membrane and has no gas exchange organs.
   Explain how a concentration gradient for oxygen is maintained across the cell surface membrane of Amoeba.2 marks
2. A locust is a terrestrial insect. Air enters through openings along the surface of its thorax and abdomen and passes into branching tubes that end next to the muscle cells. The outer surface of the locust is covered by a waterproof layer.
   Explain how the locust's gas exchange system is a compromise between gas exchange and limiting water loss.2 marks
3. In a bony fish, water passes over the gills and flows across the gill lamellae in the opposite direction to the flow of blood in the capillaries inside each lamella. Water entering the gills is 90% saturated with oxygen and leaves 20% saturated. Blood entering the lamellae is 5% saturated with oxygen and leaves 85% saturated.
   Explain how counter-current flow allows the fish to absorb a high percentage of the oxygen from the water.3 marks