What is a cell-surface membrane and what does it do?

A cell-surface membrane is a membrane surrounding cells. It acts as a barrier between the cell and its environment to control which substances enter and leave the cell. 

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What does it mean when a membrane is partially permeable?

Partially permeable means that the membrane lets some molecules through, but not others. 

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What is the name of the 1972 model used to describe cell membrane structure?

Cell membrane structure is described using the fluid mosaic model. 

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Why are cell membranes described as being fluid mosaic?

Cell membranes are described as fluid because the phospholipid molecules are constantly moving. 


They are described as mosaic because there are proteins of different sizes and shapes embedded in the phospholipid bilayer. 

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Name five components of cell-surface membranes. 

  1. Phospholipid bilayer
  2. Cholesterol
  3. Proteins
  4. Glycoproteins
  5. Glycolipids 

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Why do phospholipids form a bilayer in an aqueous environment?

Phospholipids form a bilayer because the hydrophilic heads face outwards, towards the water while the hydrophobic tails face inwards, away from the water. 

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Can most water-soluble substances pass through the phospholipid bilayer? Why?

Most water-soluble substances cannot pass through the phospholipid bilayer because the core of the bilayer is hydrophobic. 

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Which substances can pass though the phospholipid bilayer? Why?

Substances that are small and non-polar (lipid soluble). 

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What is the role of cholesterol in the cell-surface membrane?

Cholesterol provides stability and reduces fluidity. 

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Describe the roles of channel and carrier proteins in the cell-surface membrane. 

Channel and carrier proteins transport large molecules and ions across the membrane. 

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What are glycoproteins?

Glycoproteins are intrinsic proteins attached to carbohydrates.

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What are glycolipids?

Glycolipids are lipids attached to carbohydrates.

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Give three roles of glycoproteins and glycolipids.

  1. Cell adhesion
  2. Cell recognition
  3. Cell signalling 

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