Higher Biology | Key Area 2.3: Metabolic Rate

Metabolic rate

The amount of energy an organism will use within a given time.

How can metabolic rate be measured?

- Substrates and products of respiration:

- Oxygen consumption; by respirometer, O2 probe

- Carbon dioxide production; by respirometer, CO2 probe

- Heat production; by calorimeter

General rules of metabolic rate in relation to mass of organism:

- The metabolic rate increases with body mass of an organism. Larger organisms require more efficient delivery of oxygen to cells due to an increased oxygen demand.

- Birds and mammals (largest) → reptiles and amphibians → fish (smallest)

Circulatory system

Consists of the heart, blood vessels (veins, arteries, capillaries) and blood.

Respiratory system

Consists of the lungs/gills (and other structures involved in the breathing process).

The circulatory and respiratory systems

- Essential for mammals, amphibians, reptiles and fish to deliver oxygen to respiring cells.

- Have evolved to ensure efficient oxygen uptake and transport to tissues.

Complete double circulatory system

- Consists of two atria and two ventricles, where blood travels back to the heart after being oxygenated. Associated with birds and mammals.

- Ensures oxygenated and deoxygenated blood flow separately and do not mix in the heart and body.

- Enables higher metabolic rates to be maintained, as oxygenated blood can be pumped out at higher pressures, allowing more efficient oxygen delivery to cells (via large surface area, extensive blood supplies, thin walls).

Incomplete double circulatory system

- Consists of 2 atria and 1 ventricle, where blood travels back to the heart after being oxygenated. Associated with amphibians and reptiles (except crocodiles).

- Mixing of oxygenated and deoxygenated blood kept to a minimum due to timing of contractions between atria.

- Less efficient delivery of oxygen as oxygenated blood cannot be pumped at higher pressures.

Single circulatory system

- Consists of 1 atrium and 1 ventricle, where blood passes through the heart once in each complete circuit. Associated with fish.

- As blood passes through a capillary bed (eg. at the gills), blood pressure drops.

- Blood delivered to capillary tubes in body tissues is low pressure.