What is the average size of a mammalian cell?

• A. 1-2 nanometers
• B. 10-20 micrometers
• C. 100-200 micrometers
• D. 1-2 millimeters

Answer: (B)

Cells in mammals are sized to balance housing essential internal components with the need to exchange nutrients and wastes efficiently. Most mammalian cells are about 10 to 20 micrometers in diameter. That micrometer scale is small enough to keep diffusion of molecules rapid across the cell, while large enough to contain the nucleus and major organelles like mitochondria and the cytoskeleton. Nanometers are the scale of individual molecules and organelles, not whole cells, so that option would be far too small. Conversely, sizes in the hundreds of micrometers or millimeters would be impractically large for typical mammalian metabolism and diffusion; such dimensions would slow exchange processes too much. So the 10–20 micrometers range best reflects the average mammalian cell size.