Membrane

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Membrane Essay, Research Paper

The membrane has a double lipid layer through which fat- soluble substances will

move, by passive transport or diffusion. The molecules will only move through if

they are small enough. There are globular protein regions, which are

hydrophilic. These regions allow water and water soluble substances through, but

only if they are small enough, for example starch grains are too big. These

substances move through by passive transport or diffusion. Diffusion is the

passive movement of substances from a high concentration to a low concentration

( N.B., you don’t need a membrane present, e.g. diffusion occurs in the air). In

CONTRAST, diffusion of water across a semi- permeable membrane is called

OSMOSIS. Active Transport Active transport requires energy from ATP, and

involves carrier molecules studding the membranes. The carrier combines with the

molecule on the outside, which requires ATP. It then moves across, (which also

requires ATP), and returns. An example is glucose being transported by active

transport by insulin. Why is it called the Fluid Mosaic Model? Fluid- it is

called a fluid because proteins are said to wander through the membrane (hence

fluid) Mosaic- it is a mosaic because it is a collection (or mosaic) of

structures Model- because no matter how real the diagram looks, it is not real.

Therefore, it is a model. SO you put all three bits together and you get.

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