Question

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

Answer 1

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.