Diffusion in Biology (Cambridge (CIE) IGCSE Biology): Revision Note

Diffusion

What is diffusion in biology?

• Diffusion is the movement of molecules from a region of its higher concentration to a region of its lower concentration

• Molecules move down a concentration gradient, as a result of their random movement

  

• For living cells, the principle of the movement down a concentration gradient is the same, but the cell is surrounded by a cell membrane which can restrict the free movement of the molecules

• The cell membrane is a partially permeable membrane - this means it allows some molecules to cross easily, but others with difficulty or not at all

• The simplest sort of selection is based on the size of the molecules

• Diffusion helps living organisms to:

  • Obtain many of their requirements

  • Get rid of many of their waste products

  • Carry out gas exchange for respiration

Examples of diffusion in living organisms 

• Living organisms obtain various substances they need through diffusion, such as oxygen, carbon dioxide, and other nutrients.

• It is worth noting that plants require oxygen for respiration at all times, as well as carbon dioxide for photosynthesis when conditions for photosynthesis are right (e.g. enough light and a suitable temperature)

Examples of diffusion in living organisms

Where does the energy for diffusion come from?

• All particles move randomly at all times

• This is known as Brownian motion

• The energy for diffusion comes from the kinetic energy of this random movement of molecules and ions