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
Diffusion across the cell membrane
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
You will need to learn examples of substances that organisms obtain by diffusion
Don’t forget 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)
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
