what materials does cell memberane allow ? can cell memberane allow all small substances or particles which obey law of diffusion. because cell memberane only allows small particles or substances to move across through passive process?

Asked by Saurabh Vyas | 13th Sep, 2010, 12:00: AM

Expert Answer:

A few substances can diffuse directly through the lipid bilayer part of the membrane. The only substances that can do this are lipid-soluble molecules such as steroids, or very small molecules, such as H2O, O2 and CO2.
Water molecules can diffuse freely across a membrane, but always down their concentration gradient.
Facilitated diffusion allows certain ions and glucose to diffuse through the cell membrane.
Active transport uses energy and transports materials against their concentration gradient. A very important active transport system in all animals is the one that maintains sidium and potassium gradients between cells and the surrounding extracellular fluid.
Large molecules (such as proteins, polysaccharides and nucleotides) and even whole cells are moved in and out of cells by using membrane vesicles.

Answered by  | 14th Sep, 2010, 03:09: PM

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