Water is a polar solvent. All living cells exist in an aqueous internal or external environment.The phospholipid membrane is not soluble in water so forms a selectively permeable barrier to substances on either side of the membrane.Small, non-polar molecules and substances that dissolve in lipid can pass through between gaps between the hydrophobic tails of the phospholipid molecules.Organic solvents such as ethanol can dissolve the phospholipid bilayer in high enough concentrations or when pure.At lower concentrations ethanol disrupts the cell membrane and allows the passage of more substances through and impairs the proper functioning of cells.The enzyme alcohol dehydrogenase in the liver breaks down ethanol.
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Specification: OCR Biology A (H020), AS-level, 2.1.5 Biological membranes. Topic: Plasma Membrane.
Key terms in this lesson
- phospholipid bilayer
- Two layers of phospholipid molecules arranged with hydrophilic heads facing outwards and hydrophobic tails facing inwards, forming the basic structure of cell membranes.
- selectively permeable
- Describes a membrane that allows some substances to cross it but not others.
More in Plasma Membrane
- Extrinsic Proteins
- Cholesterol
- Sites of Chemical Reactions
- Effect of Temperature
- Diffusion
- Diffusion Across Membranes
- Facilitated Diffusion
- Active Transport
All 18 lessons in Plasma Membrane · All OCR AS-level Biology topics