With the use of biology microscopes, it can be observed that living cells maintain an internal composition very different from, but highly dependent upon, their milieu. This is due to a combination of active and passive transport. In particular, cells respond by changes in size and shape to changes in the osmotic activity of the environment. Such changes may be noted through biology microscopes.

The systems of active transport, especially for ions, generally respond by feedback mechanisms to changes in the external medium. Thus, compensating, at least in part, for imbalances. Somatic cells, observed under biology microscopes, are somewhat resistant to wider range of osmolality than erythrocytes. Ion transport and changes in ionic concentrations outside and inside the cells affect the transport of other nutrients.