Answer to Question #96840 in Cell Biology for Andrea

Question #96840
Describe how molecules enter and leave a cell without the use of the cell's energy
Expert's answer

Transport through cell membrane which does not require energy is called passive transport. Passive transport is performed by diffusion, facilitated diffusion, and transport through pores.

Along the path of simple diffusion, particles of a substance move through a lipid bilayer. The direction of simple diffusion is determined only by the difference in the concentrations of the substance on both sides of the membrane. Through simple diffusion hydrophobic substances (O2, N2, benzene) and polar small molecules (CO2, H2O, urea) penetrate the cell. Polar large molecules (amino acids, monosaccharides), charged particles (ions) and macromolecules (DNA, proteins) do not penetrate.

Large polar particles (amino acids, monosaccharides), charged particles (ions) pass through membranes with the help of channel proteins or carrier proteins in a process called facilitated diffusion.

Transportation through channels (pores). The channel is a section of the membrane that includes protein molecules and lipids that forms a passage in the membrane. This passage allows penetration through the membrane of water molecules, large ions.

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