The relationship between the size of an organism or structure and its surface area to volume ratio
As an organism grows larger, its volume increases faster than its surface area. This means larger organisms have less outer surface available, relative to the amount of living tissue inside.
Formula
SA:V ratio = Surface Area ÷ Volume
Real World
A warehouse-sized elephant loses heat far more slowly than a mouse of the same mass-per-unit because its SA:V ratio is much smaller — which is why Arctic mammals like polar bears are bulkier than their tropical relatives.
Exam Focus
Always show your working when calculating SA:V ratios; examiners award a method mark even if the final answer is wrong.
Evaluation Scaffold
A four-step framework for high-quality evaluation. Use this for 'assess', 'evaluate', and 'to what extent' questions.
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