Cells may frequently find themselves in an environment with very low extracellular concentrations of substances needed in higher amounts inside the cell. To obtain these needed items, such cells would be most likely to engage in- osmosis.- simple diffusion.- facilitated diffusion.- active transport.
Substances must pass through plasmatic membrane to reach the cell content. There are different possible situations:
Osmosis: water is the molecule that crosses the membrane from a solution with low solute concentration to a space with higher solute concentration (down a concentration gradient)
Simple diffusion: small molecules pass across the plasmatic membrane down a concentration gradient.
Facilitated diffusion: bigger molecules pass across the plasmatic membrane down a concentration gradient but they need special channels to do it: proteins or protein-complexes in the membrane that facilitate the transport.
Active transport: to move molecules against (up) concentration gradient, special proteins in cell membrane must use energy from ATP to bring this desired substances inside the cell.
