Surface Area to Volume Ratio

By Levi Clancy for Student Reader on
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The surface area to volume ratio restricts cell size. Large cells have less surface relative to a small cells. Large cells produce more waste, but have proportionately less surface area through which to expel that waste. This means that waste will build up inside the cell and kill the cell. In addition, large cells need more nutrients, but have proportionately less surface area through which nutrients can diffuse. This means that large cells get proportionately less nutrients and can starve to death.

  • Large cells: Low surface area to volume ratio

  • Small cells: High surface area to volume ratio.

Cell size is restricted by surface area to volume ratio. Cells become large only when they are able to expel their waste quickly, and obtain nutrients readily. There are some cells which at first seem to contradict this rule:

  • Neurons have axons which can be as long as 2 meters. They maintain a high surface area to volume ratio by making this axons extremely thin.

  • Some kelp, which can be as tall as 30 meters, are unicellular. They maintain a high surface area to volume ratio by staying extremely flat.