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A-Level Biology OCR A

Surface Area Exchange Sa:V Body Explain Volume Ratio

The decreasing surface area to volume ratio in larger organisms necessitates specialized exchange systems because surface absorption alone cannot meet the increased diffusion distances and higher oxygen demands.

A decreasing surface area to volume ratio in larger organisms lengthens diffusion distances, making it difficult or impossible for surface absorption alone to meet the body's oxygen demands, thus requiring specialized exchange systems.

Front Explain how surface area to volume ratio affects the need for a specialised exchange system.
Back SA:V & exchange systems:
  • As organisms get larger, SA:V gets smaller and distances substances need to travel from outside to reach cells in center of body get longer
  • This makes it harder and ultimately impossible to absorb enough oxygen through the available surface area to meet the demands of the body

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