Active Transport

Posted by Professor Cram in Cell Membranes

Active Transport Video

Active Transport

Active transport is the mediated process of moving molecules and other substances across membranes.

Active transport differs from passive transport in that it utilizes chemical energy in the form of adenosine triphosphate, or ATP, to move molecules against the concentration gradient — from an area of lower concentration to an area of higher concentration.

There are two types of active transport:

Primary Active Transport

Primary active transport directly utilizes chemical energy to move molecules through a membrane.

The sodium-potassium pump, present in almost all animal cells, is an example of the use of primary active transport. It expends ATP energy to move sodium ions out of the cell and replace them with potassium ions.

This exchange leaves the interior of the cell more positively charged than the cell’s exterior. This means the sodium-potassium pump must overcome not only a concentration gradient but also an electrochemical gradient as well.

Secondary Active Transport

In secondary active transport, molecules are moved through a membrane as the direct result of the diffusion of another substance.

The sodium-calcium exchanger, or antiporter, uses the normal diffusion of sodium ions into the cell to power the transport of calcium out of the cell (and across a higher concentration gradient).

In another example, the glucose symporter uses the normal diffusion of sodium ions into the cell to piggyback the transport of glucose into the cell as well.

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13 Responses to “Active Transport”

  1. sunita maharjan says:

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  2. Aaron says:

    Water does not passively pass through the cell membrane. They are polar molecules, and the only circumstance under which they can pass through the membrane alone is if it has a large amount of energy and the molecule is forced through the membrane. Water actually passes through proteins called Aquaporins, which allows diffusion with no energy -> passive diffusion

  3. Billy-Joe says:

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  4. Mrs.PhD says:

    Water passes through the cell membrane through osmosis which is a type of passive transport, hence no energy is needed, therefore it does passively pass through the plasma/cell membrane.

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  10. Fray says:

    Yooo. Don’t say water easiely passes through. Only small water molecules pass by at a particular time which is under passive transport as osmosis.
    The reason why only small molecules of H2O pass through is because that is a phospholipid layer and it is hyrophobic.

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