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Diffusion, Osmosis, Active Transport, and Passive Transport How molecules move through the membrane. Diffusion is the movement of molecules from an area where the molecule is in high concentration to an area where the molecule is in lower concentration. An example would be the food coloring in water. The food coloring (high concentration) will diffuse throughout the water (low concentration). Osmosis is the diffusion of water through a semi-permeable membrane. Water moves from an area of high water molecule concentration (and lower solute concentration) to an area of lower water molecule concentration (and higher solute concentration). Example, in the cell, water molecules can be transported through a channel, but can also diffuse directly through the membrane lipid bilayer. Active transport is the movement of molecules from areas of low concentration to areas where the molecule is found in higher concentration. This movement is not spontaneous and requires ATP energy and a protein carrier because it is moving against the concentration gradient. This process occurs continuously in nerve cell membranes with sodium-potassium pumps. Facilitated diffusion/Passive transport is the movement of a molecule from an area of high concentration to an area of lower concentration to maintain equilibrium within the cell. This type of transport requires no energy since the molecules are moving with the concentration gradient. Small molecules such as glucose or some amino acids that our cells need do this regularly. Comparison of the ways molecules move into and out of cells. Name Type of Transport Direction of Movement Conditions Examples Diffusion passive towards lower concentration Concentration gradient Water, gases (02and CO2), and steroid hormones. Osmosis passive towards lower concentration Concentration gradient, channel proteins optional Water 0nly. Active Transport active towards higher concentration Carrier protein and ATP energy Ions, sugars, and amino acids. Facilitated Diffusion/ Passive transport passive towards lower concentration Concentration gradient, plus channel or carrier proteins Water, glucose, and amino acids.