Cell Size and SA:V Ratio

See why cells remain small or increase membrane surface.

Choose a biological example

Learning mode

Guided process

Cell conditions

Cell size12 µm
Membrane folds0
Metabolic demand100%
Outside nutrient80%
Membrane permeability70%
Simulation speed1×

Live measurements



Tap the cell, membrane, nucleus or a molecule for a microscopic view.
Surface area
Volume
SA:V ratio
Supply / demand

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Narrated size lesson

Chapters

Learning objectives

  • Calculate how surface area and volume change with cell size.
  • Explain why surface-area-to-volume ratio falls as a cell grows.
  • Relate exchange capacity to metabolic demand.
  • Compare adaptations that increase effective surface area.

Key concepts

  • Surface area increases with the square of length.
  • Volume increases with the cube of length.
  • Membrane folds, thin shapes and projections increase exchange surface.
  • Cell division restores a higher surface-area-to-volume ratio.

Suggested experiments

  • Double cell size and compare the percentage changes.
  • Add membrane folds without changing volume.
  • Raise metabolic demand in a large cell.
  • Compare a sphere with a flattened or elongated cell.

Seven-question challenge

Score: 0 / 7