2.3 - Cell Size

Cell Size and Material Exchange

• Importance of Material Exchange: Cells must continuously exchange materials with their environment to obtain nutrients, eliminate waste, and manage energy.

• Impact of Cell Size:

  • Efficiency of Diffusion: Cells depend on diffusion—the movement of substances from areas of high concentration to low concentration—to facilitate these exchanges. In larger cells, diffusion may be insufficient to transport nutrients quickly across the cell, impacting efficiency.

  • Advantage of Smaller Cells: Smaller cells, with their reduced volume, generally have a more effective exchange of materials due to a favorable surface area to volume ratio.

• Surface Area to Volume Ratio (SA):

  • Critical for Exchange: The ability of a cell to exchange materials effectively is largely dependent on its surface area relative to its volume. A higher SA ratio typically means better material and energy exchange.

  • Mathematical Representation: The ratio is often expressed as SA
    or S/V, where a higher ratio indicates a greater capacity for exchange.

• Specialized Structures Enhancing Exchange:

  • Microvilli: Some cells feature specialized structures like microvilli that increase surface area, enhancing their ability to absorb nutrients and expel waste.

  • Cristae: In mitochondria, the inner membrane forms folds known as cristae, significantly increasing the surface area available for biochemical reactions that produce ATP.