(a) Measurement of oxygen consumption, carbon dioxide and heat production to compare metabolic rates.

• Metabolic rate can be measured using respirometers, oxygen probes, carbon dioxide probes and calorimeters.

(b) Organisms with high metabolic rates require more efficient delivery of oxygen to cells.

• Birds and mammals have higher metabolic rates than reptiles and amphibians, which in turn have higher metabolic rates than fish.

• Comparative anatomy and physiology of heart chambers and circulatory systems in amphibians, reptiles, mammals and birds, and heart and circulation in fish.

  • Birds and mammals have a complete double circulatory system consisting of two atria and two ventricles. 

  • Amphibians and most reptiles have an incomplete double circulatory system consisting of two atria and one ventricle. 

  • Fish have a single circulatory system consisting of one atrium and one ventricle.

  • Complete double circulatory systems enable higher metabolic rates to be maintained. 

  • There is no mixing of oxygenated and deoxygenated blood and the oxygenated blood can be pumped out at a higher pressure. 

  • This enables more efficient oxygen delivery to cells.