Explain how the body size and surface area to volume ratio of endotherms living in cold climates is an adaptation that reduces heat loss to the environment.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Bergmann's rule states that within a species of endotherm, individuals living in colder climates tend to have larger body masses than those living in warmer climates.
Model answer (4 marks)
Bergmann’s rule shows that larger endotherms have a smaller surface area to volume ratio. Heat is lost across the body surface, so a smaller surface area relative to the volume means less heat is lost per unit volume or mass. Metabolic heat is produced throughout the body volume; a larger volume therefore generates more heat relative to the surface through which it is lost. This allows the animal to maintain a stable core body temperature more efficiently in cold environments.
Examiner tips
- Use the exact phrase ‘surface area to volume ratio’
- Explain both heat loss and heat production
- Show the causal link to thermoregulation
- Keep answer to 4 clear points
Common mistakes
- Confusing surface area with total surface area of the body
- Ignoring the volume component of heat production
- Using vague terms like ‘size’ without mentioning ratio
Mark scheme (4 marks)
- Larger body size means a smaller surface area to volume ratio
- Heat is lost across the body surface, so a smaller surface area relative to volume means less heat is lost per unit volume/mass
- Metabolic heat is generated throughout the body volume, so a larger volume produces more heat relative to the surface through which it is lost
- This enables the animal to maintain a stable core body temperature (thermoregulation/homeostasis) in cold environments more efficiently
Key terms in this question
surface area to volume ratio · endotherm
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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