Variations in Cell Size:

Cells vary greatly in size. The smallest cells are bacteria called Mycoplasma, with diameter between 0.1 µm to 1.0 µm. The bulkiest cells are bird eggs, and the longest cells are some muscle cells and nerve cells. Most cells lie between these extremes.

Importance of Cell Sizes or Relation of Cell Size With Function:

Cell size and shape are related to cell function.
Bird eggs are bulky because they contain a large amount of nutrients for the developing young.
Long muscle cells are efficient in pulling different body parts together.
lengthy nerve cells can transmit messages between different parts of the body.
Small cell size also has many benefits, For example human red blood cells are only 8µm in diameter and therefore can move through our tiniest blood vessels i.e., capillaries.

Variation in Surface to Volume Ratio:

Most cells are small in size. In relation to their volumes, large cells have less surface area as compared to small cells.

Importance of Surface to Volume Ratio:

Need of nutrients and the rate of waste production are directly proportional to cell volume. Cell takes up nutrients and excretes wastes through its surface cell membrane. So a large volume cell demands large surface area.