Cell size and surface area to volume Ratio:

Cells vary greatly in size.

Mycoplasmas:

The smallest cells are bacteria called mycoplasmas, with diameter between 0.1 µ to 1.0 µ m.

Bulkiest cells:

The bulkiest cells are bird eggs, and the longest cells are some muscle cells and nerve cells. Most cells lie between these extremes.

Note:

Most cells are small in size. Large cells have less surface area in relation to their volume while small cells of the same shape have more surface area.

The surface-to-volume relationship of cube-shaped cells:

The figure shows 1 large cell and 27 small cells. In both cases the total volume is the same:

Volume = 30 µ m 30 m x 30 µ m = 27,000 µ m³

Total surface areas:

In contrast to the total volume, the total surface areas are very different. Because the cubical shape has 6 sides, its surface area is 6 times the area of 1 side. The surface areas of the cubes are as follows:

Surface area of 1 large cube = 6 x (30 µ m x 30 µ m) = 5400 µ m²

Surface area of 1 small cube = 6 x (10 µ x 10 µ m) = 600 µ m² and

Surface area of 27 small cubes = 27 x 600 µ m = 16.200 µ m²

This relationship between cell size and surface area to volume ratio works to limit cell size.

As the size of a cell increases, cell volume increases more rapidly than its surface area.

Effect of cell size on surface area