Unformatted text preview: Cross ‐ Membrane Transport Concentration gradients by which diffusion and osmosis operate are only partially effective when all needs of the plant are considered. Some essential materials, for example, are present in small amounts in the soil but used in greater concentrations by the plant. How do the plants retain such materials as they accumulate in cells against the concentration gradient? Or, how is it possible for plants to get rid of unneeded or toxic substances that diffuse inward? Three means of transport take place: passive, active, and vesicle. Passive transport Simple diffusion . Some materials, like water, simply diffuse across the cell's membrane as a function of the concentration gradient across the membrane, i.e. they move from a region of their higher concentration to a region of their lower concentration through the phospholipid layer. Materials higher concentration to a region of their lower concentration through the phospholipid layer....
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- Fall '08