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Active Transport

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Unlike diffusion, osmosis and facilitated diffusion, active transport requires energy in the form of ATP (adenosine triphosphate), and moves substances against a concentration gradient (from a lower concentration to a higher concentration). This process is essential in removing of all toxins from the body, as well as the movement of rare chemicals.

Active transport is achieved by specific carrier proteins in the plasma membrane, and relies on adequate oxygen supply (which results in ATP being available). Here's a quick video that shows the process:

There are certain cells which carry our active transport more than others, for example in the kidney. These cells have special adaptations, such as microvilli for increased surface area, hence more carrier proteins available, as well as many mitochondria for the production of ATP.