When we think “physiology”, we think about functions, chemical and biochemical processes that occur in the cell; these functions occur in “time and space” inside the cells. The problem lays in the experimental approach: in order to study functions you need a living cell, because a fixed one can maintain some structures but not its functions. The cell must be studied while it is living without altering too much its functions. Thus, the first very important thing is that cell physiology studies the cell during its life in time and space.