Shape and structure of cell
Cell is a simple sphere, well-defined structure, with extended process for example neuron or epithelial cells that have distinct apical and basolateral surfaces carrying out distinct functions. The abilities of cells to take such different forms depends on the following:
· Separation of a membrane called plasma membrane from the external environment which control import and export
· Cellular components that are constructed by food sources
· Genetic information and gene expression
For unicellular organisms, homeostasis is necessary because the exterior environment may be subjected to significant fluctuations. For multicellular organisms, it enables individual cells to maintain internal environments that are distinct from that of the extracellular fluid.
The cell responds to this situation by controlling the movement of ions and water across the plasma membrane. Its ability to maintain a constant internal environment is called homeostasis. This is an important function of all cells, whether they are part of unicellular or multicellular organisms. One major role of homeostasis in animal cells is to cope with osmotic pressure by balancing the ionic composition so as to avoid the accumulation of water. To maintain homeostasis, ions and water may need to be moved into or out of a cell in a regulated manner.
The cell membrane regulates movement of water and ions. The difference in permeability to water and to ionic solutes has an important consequence in allowing osmotic pressure to develop across the membrane in response to differences in concentrations of dissolved substances on either side. Typically, the interior of the cell has higher potassium but lower sodium and calcium concentrations than that in the exterior. Sodium or potassium ions can diffuse less than the rate of water diffusion. So, there is a difference in ion concentrations on either side of the membrane. Water moves across to equalize the concentration of solutes on either side. If a cell had no mechanism to control solute levels, it would shrink or expand in response to osmotic pressure, whenever the concentration of solutes outside was greater than inside or vice versa.