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Edexcel ·Biology·Cambridge AS & A Level Biology

Cell Membranes & Transport

16 min read

The fluid mosaic model, membrane components, and diffusion, osmosis, active transport, endocytosis and exocytosis.

The fluid mosaic model

The membrane is a phospholipid bilayer with hydrophilic heads facing the watery surroundings and hydrophobic tails inward. Proteins are embedded in a "mosaic" and the whole structure is "fluid" — phospholipids move laterally.

Components and roles:

    Phospholipids — form the bilayer barrier to water-soluble substances.
    Cholesterol — fits between phospholipids, regulating fluidity and stability (less fluid at high temperature, prevents stiffening at low temperature).
    Intrinsic (integral) proteins — channel and carrier proteins for transport.
    Glycoproteins / glycolipids — cell recognition, receptors, antigens.

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