AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Diffusion is the spreading out of the particles of any substance in…
Full specification wording
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 the passive spreading out of particles.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 2 of 11
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Diffusion is the passive spreading out of particles. It applies to particles of a substance in solution and to particles of a gas. The particles move randomly in all directions, but if one region has a higher concentration than another, there are more particles moving away from the high-concentration region than into it. This produces a net movement from higher concentration to lower concentration. Eventually the concentrations become equal and there is no net movement, although particles continue to move randomly. A familiar example is a drop of ink spreading through water until the colour is even. The statement is assessed by asking you to define diffusion precisely, including the type of particles and the direction of net movement.
What earns the marks
- Diffusion involves the spreading out of particles of a substance in solution or particles of a gas.
- Particles move randomly, which causes them to spread from where they are more concentrated.
- There is a net movement from an area of higher concentration to an area of lower concentration.
- Net movement means the overall movement, even though individual particles move in all directions.
- Diffusion continues until the concentration is uniform, after which there is no net movement.
- Diffusion is a passive process and does not require energy from respiration.
Common mistakes and how to put them right
Defining diffusion as movement only from high to low concentration without mentioning random particle movement.
Put it right: Include both the random motion and the net direction.
Saying particles stop moving when concentrations are equal.
Put it right: Particles continue to move randomly but there is no net movement.
Applying diffusion only to gases.
Put it right: Particles of substances in solution also diffuse.
Exam tips
- Use the words net movement and concentration gradient to make the definition precise.
- State that particles are in solution or in a gas, because this matches the specification wording.
- If asked to explain, link random particle motion to the overall net direction.
Try the lesson
The start of the 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. lesson, made from checked teaching notes for this specification point.
Have a go first
Which sentence gives the correct meaning of diffusion?
Listen
Diffusion is the passive spreading out of particles. It applies to particles of a substance in solution and to particles of a gas. The particles move randomly in all directions, but if one region has a higher concentration than another, there are more particles moving away from the high-concentration region than into it. This produces a net movement from higher concentration to lower concentration. Eventually the concentrations become equal and there is no net movement, although particles continue to move randomly. A familiar example is a drop of ink spreading through water until the colour is even. The statement is assessed by asking you to define diffusion precisely, including the type of particles and the direction of net movement. A strong answer earns marks for these points. Diffusion involves the spreading out of particles of a substance in solution or particles of a gas. Particles move randomly, which causes them to spread from where they are more concentrated. There is a net movement from an area of higher concentration to an area of lower concentration. Net movement means the overall movement, even though individual particles move in all directions. A common slip: Defining diffusion as movement only from high to low concentration without mentioning random particle movement. Instead, include both the random motion and the net direction. Exam tip: Use the words net movement and concentration gradient to make the definition precise.
Key words
Say what each word means before you turn the card.
Diffusion
Try answering aloud or in your head before turning the card.
Random motion
Try answering aloud or in your head before turning the card.
Net movement
Try answering aloud or in your head before turning the card.
See every definition
- Diffusion
- 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.
- Random motion
- The way particles move randomly in all directions, which causes them to spread from where they are more concentrated.
- Net movement
- The overall movement from an area of higher concentration to an area of lower concentration, even though individual particles move in all directions.
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of 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.
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge