Algebraic substitution
Don’t feel so confident about calculating surface area to volume ratio? It might help to review how to substitute values into algebraic equations.
Surface area to volume ratio
Understanding the surface area to volume ratio helps us understand how cells efficiently manage transport and exchange with the environment. This affects how cells take in nutrients and get rid of waste. Use this resource to learn how this ratio impacts cell size and function in biology.
The surface area to volume ratio is a measure that compares the size of a cell's surface to its volume. Surface area is the total area of the cell's outer membrane, and volume is the amount of space inside the cell. Sometimes, you may see surface area to volume ratio being written as SA:V.
The difference in the surface area and volume of a cube is shown.
Surface area of a cube
A three-dimensional cube and a two-dimensional net of a cube. The sides of the cube are 2 centimetres long. The volume of the cube is 2 times 2 times 2 equals 8 centimetres cubed. The net of the cube also has sides of 2 centimetres. The surface area of the cube, based on its net, is 2 times 2 centimetres times 6 faces, which is equal to 24 centimetres squared.
Effect of surface area to volume ratio on cell function
A high surface area to volume ratio is important for cell function. The following table highlights specific ways in which a high surface area to volume ratio supports cells.
| High SA:V ... | by ... |
|---|---|
| enhances nutrient uptake | allowing for more efficient absorption of nutrients from the environment. |
| improves waste removal | enabling quicker and more effective transport of waste products out of the cell. |
| increases gas exchange | optimising the exchange of gases like oxygen and carbon dioxide, which are needed for cellular respiration and survival. |
| supports faster communication | allowing signals and materials to be distributed more quickly within the cell and between cel. |
| allows the cell to adapt more quickly to change | enabling cells to react more quickly to changes by speeding up internal and external exchanges. |
A high surface area to volume ratio makes the exchange of nutrients and waste more efficient between the cell and its environment; it maximises the rate of diffusion.
Effect of surface area to volume ratio on cell size
Why are cells so small? The surface area to volume ratio is a key factor in determining the size of a cell.
As a cell grows, its volume increases faster than its surface area. This reduces the ratio and makes it harder for the cell to efficiently take up nutrients and expel waste. To function well, most cells stay small or have adaptations like microvilli (small projections) to increase surface area. Think of them like the bristles of a brush. Just as the many bristles increase the surface area of the brush for cleaning, microvilli increase the cell's surface area to enhance absorption and exchange of materials.
Intestinal epithelial cells are examples of cells that have microvilli to increase their surface area. These cells line the intestine and are involved in absorption of nutrients. The presence of microvilli makes the absorption process more efficient.
This ratio helps explain why cells are usually so small.
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