How Diffusion Works
Explain diffusion as the net movement of particles from a region of higher concentration to lower concentration, and describe its role in moving materials (oxygen, carbon dioxide, glucose) in and between cells
What a learner can do afterwards
- Defines diffusion using particle theory
- Explains the direction of diffusion of oxygen and carbon dioxide at the alveoli
- Explains how cells get glucose from the blood using diffusion
- Identifies factors that affect the rate of diffusion (concentration gradient, surface area, distance)
The lesson
You already know a cell has a membrane around it. Diffusion is one way substances cross that membrane, and no pumping is needed. Every particle in a liquid or gas is always moving in random directions. When one area has more particles than another, this random motion causes a net movement from the crowded area to the emptier area, until the particles spread out evenly.
In your lungs, tiny air sacs called alveoli sit next to blood vessels. The air you breathe in has a high concentration of oxygen, and the blood arriving there has a low concentration of oxygen, so oxygen diffuses from the air into the blood. At the same time, the blood has a high concentration of carbon dioxide, and the air has a low concentration, so carbon dioxide diffuses the other way, from blood into air.
After you eat, your blood carries a high concentration of glucose. A body cell uses up glucose for energy, so the concentration inside the cell is often lower than in the blood next to it. Glucose diffuses from the blood, through the cell membrane, into the cell, moving from high concentration to low concentration.
Diffusion happens faster when the concentration gradient is steeper, when the surface area for particles to cross is larger, and when the distance particles must travel is shorter.
Diffusion is the net movement of particles from high to low concentration, and it moves oxygen, carbon dioxide, and glucose in and out of cells without the body using energy to pump them.
Watch it
Where it sits
Learn first
This opens up
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.