Apr 3
In this free science revision tuition programme sample, we look at diffusion.

Diffusion is the thing that allows you to smell a great meal being cooked downstairs while you are upstairs. It is the movement of particles in a solution or gas from an area of high concentration to an area of low concentration.

Movement of particles
You need to think about the arrangement of particles and remember that gases have lots of energy and are constantly moving in random motion.
When they collide with the particles that are in a high concentration, they move them about the gas. We call this dissipation.

The same thing happens in liquids because liquids are able to flow over each other.

Essential process
Diffusion is an essential process for all living things; it means oxygen enters our cells and carbon dioxide leaves as oxygen is in a higher concentration outside the cell than inside, and the reverse is true for carbon dioxide.

These are simple molecules that can diffuse easily through the cell membrane. Not all molecules are small enough to do this, such as large proteins.

Examples of diffusion
So, some examples of diffusion in plant and animal cells are oxygen into the blood in the lungs and carbon dioxide out of the blood into the air at the lungs. The higher the concentration gradient, the faster the diffusion happens.

Plant cells need carbon dioxide for photosynthesis, so carbon dioxide will be in a lower concentration in the cell than outside it, so it will diffuse into the cell.

Increasing and decreasing diffusion
Several factors can increase the diffusion rate, one of which we have already mentioned – concentration gradient. The larger the difference between the two sides of the membrane, the faster diffusion happens.

Diffusion happens faster at higher temperatures as the particles have more energy and move faster and more randomly.

The other factor is the membrane’s surface area and thickness. The larger the surface area, the faster the diffusion rate (remember, the rate is something happening over time). The thinner the membrane, the faster the rate of diffusion.

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