MS3- Metabolic rate

• An organism's metabolic rate is the amount of energy expended by that organism in a given time period- usually daily
• The metabolic rate can be measured in different ways:

  • oxygen consumption
  • carbon dioxide production
  • heat production
• A respirometer is used to measure the oxygen consumption of an organism
• An organism's metabolic rate can also be calculated using a calorimeter, a piece of equipment used to measure heat production
• Oxygen, carbon dioxide, and temperature probes can all be used to help calculate an organism's metabolic rate
• Oxygen is consumed during aerobic respiration. If the rate at which energy is demanded rises, then so too must the rate of oxygen delivery
• In simple organisms, oxygen can dissolve and diffuse through cell membranes
• However, with increasing complexity, multi-cellular organisms must devise oxygen delivery systems
• This gives rise to the cardiovascular systems seen in higher animals
• 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
• Fish have a circulatory system where blood passes through the heart once in each complete circuit of the body
• Fish have a two-chambered heart consisting of one atrium and one ventricle
• Amphibians and most reptiles have an incomplete double circulatory system
• Amphibians and most reptiles have a three chambered heart consisting of two atria and one ventricle
• Birds and mammals have a complete double circulatory system
• Birds and mammals have a four-chambered heart consisting of two atria and two ventricles
• There is no mixing of oxygenated and deoxygenated blood and the oxygenated blood can be pumped out at higher pressure
• This enables more efficient oxygen delivery to cells
• Birds and mammals have a high energy demand which requires efficient delivery of oxygen to the tissues
• Complete double circulatory systems enable higher metabolic rates to be maintained