exchange across the plasma membrane

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Diffusion  is the passive movement of particles from a high concentration to a low concentration (down the gradient). Factors such as a large surface area (microvilli), thin exchange surface and a high concentration gradient all increace the rate of diffusion.


Osmosis is the net movement of particles over a partially permeable membrane from an area of high water potential to an area of low water potential.

Facillitated Diffusion

This is used when larger molecules need to be excanged over the plasma membrane but cant do so by themselves. Instead, the molecules use carrier proteins or protein channels in order to move over the membrane.

Carrier proteins

The large molecule attaches to the protein, which then changes shape and allows the molecue to move into the low concentration.

Channel Proteins

Channel proteins allow charged particles to exchange over the membrane, and each channel is specific to a certain particle. The protein creates a pore in order to allow the charged particles to pass over into the lower concentration gradient.

Active Transport

Active transport uses energy in order to transport molecules and ions across the plasma membrane from a low concentration to a higher concentration (against the gradient).

Active transport uses Carrier Proteins or Co-transporters.

Carrier Proteins

A molecule or an ion attaches to the wall of the carrier protein. The protein then changes shape using ATP as a form of energy and releases…


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