Explanation:
-sandwich
In the fluid mosaic model, the plasma membrane contains a lipid bilayer with embedded prteins, which functions to hold the cell's contents together- like slices of bread. The cell's contents, including organelles and other components, are kept contained by the membrane- not unlike sandwich fillings or components.
Further explanation:
Lipids are composed of fatty acids which form the hydrophobic tail and glycerol which forms the hydrophilic head; glycerol is a 3-Carbon alcohol which is water soluble, while the fatty acid tail is a long chain hydrocarbon (hydrogens attached to a carbon backbone) with up to 36 carbons. Their polarity or arrangement can give these non-polar macromolecules hydrophilic and hydrophobic properties i.e. they are amphiphilic.
The polar nature of the membrane’s surface can attract polar molecules, where they can later be transported through various mechanisms. Also, the non-polar region of the membrane allows for the movement of small non-polar molecules across the membrane’s interior, while preventing the movement of polar molecules, thus maintaining the cell’s composition of solutes and other substances by limiting their movement.
Via diffusion, small water molecules can move across the phospholipid bilayer acts as a semi-permeable membrane into the extracellular fluid or the cytoplasm which are both hydrophilic and contain large concentrations of polar water molecules or other water-soluble compounds.
Similarly via osmosis, the water passes through the membrane due to the difference in osmotic pressure on either side of the phospholipid bilayer, this means that the water moves from regions of high osmotic pressure/concentration to regions of low pressure/ concentration to a steady state.
Transmembrane proteins are embedded within the membrane from the extracellular fluid to the cytoplasm, and are sometimes attached to glycoproteins (proteins attached to carbohydrates) which function as cell surface markers. Carrier proteins and channel proteins are the two major classes of membrane transport proteins; these allow large molecules called solutes (including essential biomolecules) to cross the membrane.
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