SA:V Ratio & Metabolic Rate (AQA A Level Biology)

The Relationship between Surface Area: Volume Ratio & Metabolic Rate

• The metabolic rate of an organism is the amount of energy expended by that organism within a given period of time

• The basal metabolic rate (BMR) is the metabolic rate of an organism when at rest. The BMR is significantly lower than when an organism is actively moving

• During periods of rest, the body of an organism only requires energy for the functioning of vital organs such as the lungs, heart and brain

• The metabolic rate of an organism can be measured/estimate using different methods:

  • Oxygen consumption

  • Carbon dioxide production

  • Heat production

Metabolic rate increases with body mass

Body Mass

• Experiments conducted by scientists have shown that the greater the mass of an organism, the higher the metabolic rate

  • Therefore, a single rhino consumes more oxygen within a given period of time compared to a single mouse

SA:V Ratio

• Although metabolic rate increases with body mass the BMR per unit of body mass is higher in smaller animals than in larger animals

  • Smaller animals have a greater SA:V ratio so they lose more heat, meaning they have to use up more energy to maintain their body temperature

• Different apparatus can be used for investigating metabolic rates in organisms:

  • Respirometers

  • Oxygen/carbon dioxide probes

  • Calorimeters