what is the important function of cell membrane regarding to diffusion?

The cell membrane is found in both animal and plant cell and it consists of plasma proteins. It is semi permeable, soft and elastic. It is selectively permeable to ions and organic molecules and the movement of substances in and out of cells are controlled by plasma membrane. Diffusion is one of the important cell membrane transport mechanisms. 

Substances like CO2 O2 and water can move across the cell membrane by diffusion. It is a passive transport process. When molecules move via special transport proteins found within the cell membrane, it is called facilitated diffusion. The cell membrane acts as a barrier for certain molecules and ions, they can occur in different concentrations (High & Low) on the two sides of the membrane. Such a concentration gradient across a semipermeable membrane sets up an osmotic flow for the water. Diffusion does not involve chemical energy.

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  Substances, such as water, ions, and molecules needed for cellular processes, can enter and leave cells by a passive process such as diffusion. Diffusion is random movement of molecules but has a net direction toward regions of lower concentration in order to reach an equillibrium.

Simple passive diffusion occurs when small molecules pass through the lipid bilayer of a cell membrane. Facilitated diffusion depends on carrier proteins imbedded in the membrane to allow specific substances to pass through, that might not be able to diffuse through the cell membrane.

 

Importance: The rate of diffusion is affected by properties of the cell, the diffusing molecule, and the surrounding solution. We can use simple equations and graphs to examine how particular molecules and their concentration affect the rate of diffusion. We can also compare simple and facilitated diffusion.

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