SA:V and heat transfer
Thermal energy leaves an animal across its body surface. SA:V therefore determines how much heat-transferring surface is available in relation to the amount of body tissue.
For a smaller animal, surface area is large in proportion to volume, giving a high SA:V ratio. Heat loss is therefore greater relative to its size.
For a larger animal, surface area forms a smaller proportion of its volume, giving a low SA:V ratio. It consequently loses less heat relative to its size.
1 Small animal
- High SA:V ratio
- More heat-transfer surface for each unit of volume
- Greater heat loss relative to body size
2 Large animal
- Low SA:V ratio
- Less heat-transfer surface for each unit of volume
- Lower heat loss relative to body size
This does not mean that a small animal has the larger total body surface. A large animal may have much more surface overall, but it has less surface in proportion to its volume.
Exam Tip: In a heat-loss explanation, compare surface area with volume. State that a high SA:V provides more surface for heat transfer for a given amount of body tissue; do not state that the smaller animal has the greater total surface area.