Briefly explain what it means for a membrane to be selectively permeable. What kinds of molecules can pass freely? What needs help getting through? Is energy always required and when is it needed?
Briefly explain what it means for a membrane to be selectively permeable.
What kinds of molecules can pass freely? What needs help getting through? Is energy always required and when is it needed?
The cell membrane is a biological membrane that separates the interior of all cells from the outside environment (the extracellular space) which protects the cell from its environment.
Semi-permeable membrane or selectively permeable means that the membrane allows certain molecules or ions to pass through it, while restricts the movement of other molecules.
The structure of the lipid bilayer allows small, uncharged substances such as oxygen and carbon dioxide, and hydrophobic molecules such as lipids, to pass through the cell membrane, down their concentration gradient, by the process of simple diffusion.
Facilitated diffusion, therefore, allows polar and charged molecules, such as carbohydrates, amino acids, nucleotides, and ions, to cross the plasma membrane. Two classes of proteins that mediate facilitated diffusion are generally distinguished: carrier proteins and channel proteins.
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