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Question

What is the composition of the cell membrane?
How do molecules move in this selectively permeable membrane? [3 MARKS]


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Solution

Naming: 1 Mark
Explanation: 1 Mark each.

A cell’s outer membrane is composed of a combination of proteins and fats called lipids. Lipids give membranes their flexibility. Proteins transmit chemical messages inside the cell.

Molecules move inside the cell by two means of transport.

  • Passive transport:
  • The molecules move through the cytoplasm by means of diffusion and osmotic pressure.
  • No external energy is used.
  • This is a slow process.
  • Active transport:
  • Here the molecules move using external energy provided by the mitochondria in the form of ATP.
  • This is a rapid process
  • Usually unidirectional.

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