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National 5 Transport across membranesAll cells are enclosed by a cell membrane, which is selectively permeable. Molecules can move into or out of cells by diffusion and active transport. Cells can gain or lose water by osmosis. Part of Biology Cell biology
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DiffusionMolecules can move into or out of cells by the process of diffusion. The video below shows how you can investigate diffusion and selective permeability using a model cell. download TranscriptDownloadTranscriptDiffusion is the net movement of molecules from an area where they are at a higher concentration to areas where they are at a lower concentration. This is due to the random movement of the molecules. The difference in the concentration of a substance between two areas is called the concentration gradient. The bigger the difference, the steeper the concentration gradient and the faster the molecules of a substance will diffuse. The direction of diffusion is said to be 'down' or 'with' the concentration gradient. Diffusion stops when the concentration of the substance is equal in both areas. This does not mean that the molecules of substance are not moving any more, just that there is no overall movement in one direction. Molecules of substance are moving equally in both directions. Diffusion can be observed by placing potassium permanganate into a beaker of water. The crystals begin to diffuse into the water to give layers of different concentrations. After one hour, equilibrium has been reached which means the potassium permanganate crystals are at an equal concentration throughout the water. Diffusion has stopped.
National 5 Subjects
What is the movement of molecules from higher concentration to lower concentration?Diffusion: Diffusion is the movement of particles from an area of higher concentration to lower concentration. The overall effect is to equalize concentration throughout the medium.
What is the movement of molecules from an area of lower concentration to one of higher concentration with carrier molecules using energy called?The movement of molecules across a membrane without the input of energy is known as passive transport. When energy (ATP) is needed, the movement is known as active transport. Active transport moves molecules against their concentration gradient, from an area of low concentration to an area of high concentration.
What is the movement of molecules from an area of high to low concentration and does not require energy?The movement of molecules from an area of higher concentration to an area of lower concentration is called diffusion.
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What is movement of molecules from an area of higher concentration to an area of lower concentration?
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