# Explain why a large surface area to volume ratio makes it more difficult for an organism to maintain a stable internal environment.

> OCR A-Level Biology A (H420) — 5.1 Communication and homeostasis · Explain · 4 marks

> Multicellular organisms have evolved complex communication and homeostatic systems. The need for such systems is linked, in part, to the relationship between an organism's size and its surface area relative to its volume.

## Mark scheme (4 marks)

1. A large SA:V ratio means a greater relative surface area across which heat or substances can be lost or gained by diffusion/conduction
2. Internal conditions (e.g. temperature, water potential, ion concentration) therefore change more rapidly / fluctuate more
3. This means corrective homeostatic responses must be triggered more frequently or with greater magnitude to counteract deviations from the set point
4. This requires a greater expenditure of energy / metabolic resources to maintain homeostasis, making it more difficult to sustain a stable internal environment

## Key terms

- [surface area to volume ratio](https://www.gradenine.co.uk/glossary/surface-area-to-volume-ratio)
- [internal environment](https://www.gradenine.co.uk/glossary/internal-environment)

## Related

- [Revision notes for OCR A-Level Biology A (H420)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-a-large-surface-area-b73b3492) · Published by Druglandscape Ltd.