Changes to body shape and the development of systems in larger organisms as adaptations that facilitate exchange as this ratio reduces
As organisms get larger, their surface area to volume ratio falls. Larger organisms compensate by changing body shape or evolving specialised exchange systems, such as lungs or gills.
Real World
The flatworm Planaria has no circulatory or respiratory system but survives because its flattened body keeps every cell within 1–2 mm of the surface, allowing oxygen to reach all cells by diffusion alone.
Exam Focus
Link each adaptation explicitly to SA:V ratio — state that it 'increases surface area relative to volume' to secure application marks.
Evaluation Scaffold
A four-step framework for high-quality evaluation. Use this for 'assess', 'evaluate', and 'to what extent' questions.
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