SA : Vol Ratio

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•  Surface area to volume ratio is important in the limitation of cell size

Cells need to produce chemical energy (via metabolism) to survive and this requires the exchange of materials with the environment

  • The rate of metabolism of a cell is a function of its mass / volume  (larger cells need more energy to sustain essential functions)
  • The rate of material exchange is a function of its surface area  (large membrane surface equates to more material movement)

As a cell grows, volume (units3) increases faster than surface area (units2), leading to a decreased SA:Vol ratio

  • If metabolic rate exceeds the rate of exchange of vital materials and wastes (low SA:Vol ratio), the cell will eventually die
  • Hence growing cells tend to divide and remain small in order to maintain a high SA:Vol ratio suitable for survival

Overview of Surface Area to Volume Ratio

SA-Vol ratio

Increasing SA:Vol Ratio

Cells and tissues that are specialised for gas or material exchanges will increase their surface area to optimise material transfer

  • Intestinal tissue of the digestive tract may form a ruffled structure (villi) to increase the surface area of the inner lining
  • Alveoli within the lungs have membranous extensions called microvilli, which function to increase the total membrane surface

villi and microvilli