Diffusion
Cambridge IGCSE Biology (0610) · Unit 3: Movement into and out of cells · 10 flashcards
Diffusion is topic 3.1 in the Cambridge IGCSE Biology (0610) syllabus , positioned in Unit 3 — Movement into and out of cells , alongside Osmosis and Active transport. In one line: Diffusion is the net movement of particles from a region of their higher concentration to a region of their lower concentration (down a concentration gradient) due to their random movement.
This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). Past papers from 2022 to 2025 record 1 explicit question on this topic — though the concept underpins many adjacent topics, so it is tested far more often than that figure suggests.
The deck below contains 10 flashcards — 1 definition, 6 key concepts, 1 process card and 2 application cards — covering the precise wording mark schemes reward. Use the definition card to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.
Diffusion
Diffusion is the net movement of particles from a region of their higher concentration to a region of their lower concentration (down a concentration gradient) due to their random movement.
What the Cambridge 0610 syllabus says
Official 2026-2028 specThese are the exact learning objectives Cambridge sets for this topic. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks.
- Describe Describe diffusion as the net movement of particles from a region of their higher concentration to a region of their lower concentration (i.e. down a concentration gradient), as a result of their random movement
- State State that the energy for diffusion comes from the kinetic energy of random movement of molecules and ions
- State State that some substances move into and out of cells by diffusion through the cell membrane
- Describe Describe the importance of diffusion of gases and solutes in living organisms
- Investigate Investigate the factors that influence diffusion, limited to: surface area, temperature, concentration gradient and distance
Define diffusion.
Diffusion is the net movement of particles from a region of their higher concentration to a region of their lower concentration (down a concentration gradient) due to their random movement.
Where does the energy for diffusion come from?
The energy for diffusion is derived from the kinetic energy of the random movement of molecules and ions. Increased temperature leads to faster movement and, therefore, a faster rate of diffusion.
How do some substances move into and out of cells?
Some substances, like oxygen and carbon dioxide, move into and out of cells by diffusion through the cell membrane. The cell membrane is partially permeable, allowing only small, non-polar molecules to pass directly.
Why is the diffusion of oxygen and carbon dioxide important in plants?
Oxygen is important for aerobic respiration, generating energy for the cells. Carbon dioxide diffuses into the leaf for photosynthesis to make food and diffuses out as a waste product of respiration.
Why is the diffusion of oxygen and carbon dioxide important in animals?
Oxygen is transported from the lungs to respiring tissues in the body, facilitating energy release. Carbon dioxide moves from the respiring tissues to the lungs and gets exhaled as waste.
How does surface area affect the rate of diffusion?
A larger surface area increases the rate of diffusion. The small intestine has villi to increase surface area for efficient absorption of digested food into the bloodstream.
How does temperature affect the rate of diffusion?
An increase in temperature increases the rate of diffusion. Higher temperatures provide more kinetic energy to the molecules, causing them to move faster and increasing diffusion rate.
How does the concentration gradient affect the rate of diffusion?
A steeper concentration gradient (larger difference in concentration) increases the rate of diffusion. The greater the difference, the faster the net movement of particles.
How does distance affect the rate of diffusion?
A shorter distance decreases the time it takes for diffusion to occur, increasing the rate. Diffusion is only efficient over short distances because the rate of diffusion is inversely proportional to the square of the distance.
Give examples of molecules that move via diffusion through cell membranes.
Small, non-polar molecules like oxygen (O2), carbon dioxide (CO2), and urea readily move across cell membranes via diffusion due to their chemical properties. Large or polar molecules need carrier/channel proteins.
Key Questions: Diffusion
Define diffusion.
Diffusion is the net movement of particles from a region of their higher concentration to a region of their lower concentration (down a concentration gradient) due to their random movement.
Tips to avoid common mistakes in Diffusion
- ● Nail the definition of osmosis: the net movement of water molecules from a region of high water potential to a region of low water potential, through a partially permeable membrane.
- ● Always consider how surface area affects diffusion rate — more surface means faster diffusion.
- ● Master the four factors that affect diffusion: concentration gradient, surface area, temperature, and diffusion distance — steeper gradients, higher temps, and larger areas all *increase* diffusion rate.
- ● Burn this into your memory: diffusion moves particles down a concentration gradient, and it's a passive process (no ATP needed).
- ● Diffusion's rate goes up with surface area, concentration gradient, and temperature — remember all three factors.
More topics in Unit 3 — Movement into and out of cells
Diffusion sits alongside these Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 0610 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Key terms covered in this Diffusion deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
Related Biology guides
Long-read articles that go beyond the deck — cover the whole subject's common mistakes, high-yield content and revision pacing.
How to study this Diffusion deck
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