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
Examiner Tip
Plants have much lower metabolic rates than animals as they do not move around their habitat and don’t have to maintain a high body temperature.
