Diffusion | 9-1 GCSE Science Biology | OCR, AQA, Edexcel

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They key points covered in this video include:
1. How are things transported in cells?
2. What is diffusion?
3. How does diffusion work across cell membranes?

How are Substances Transported in Cells?

Substances can be transported in and out of cells through diffusion, osmosis and active transport. These processes move things through the cell membrane.

What is Diffusion?

Diffusion is the spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an area of lower concentration. Diffusion is a term for particles spreading from one area to another. The particles move from an area of high concentration to low concentration. This is called moving down a concentration gradient. Diffusion happens in gases and solutions. It does not require any energy - it is passive.

How does Diffusion Work Across Cell Membranes?

Cell membranes allow the diffusion of substances in and out. This is because they have small holes in them - this makes them partially permeable. They are called partially permeable because they only let some things through. Small molecules like water and amino acids can go through but not larger molecules like proteins and starch. Particles, such as glucose, move from a higher concentration to a lower concentration through small holes. They always move down the concentration gradient. The movement of particles is random so they go both ways - what is important is the overall (or net) movement of particles.

Summary
1. We can transport things out of cells through active transport, diffusion and osmosis
2. Diffusion is the movement of particles from an area of high concentration to low concentration
3. Diffusion is passive - this means it does not require any energy
4. Diffusion can move particles through the cell membrane