# Diffusion The spreading out of particles from where there are lots of them to where there are fewer. It needs no energy. Biology (school) · Part 02: Moving materials, enzymes and energy · Card 1 of 11 · Last updated 2026-10-19 ## Analogy The smell of perfume spreading across a room. ## In practice Oxygen diffuses from the air in your lungs into your blood. ## Practice ### Flashcards - **Does diffusion need energy from respiration?** No. It is passive and moves particles down a concentration gradient. ### Interview questions **Explain the difference between diffusion, osmosis and active transport.** - Diffusion is the spreading of particles down a concentration gradient - Osmosis is diffusion of water through a partially permeable membrane - Active transport moves particles against the gradient - Active transport needs energy from respiration ## Questions people ask ### What affects the rate of diffusion? Three things matter most. A steeper concentration gradient makes diffusion faster. A higher temperature gives particles more energy, so they move faster. A larger surface area gives more room for particles to cross. This is why lungs and the gut have huge folded surfaces. ### What is a concentration gradient? A concentration gradient is the difference in how many particles there are in two places. Particles move down the gradient from the crowded area to the less crowded area. The bigger the difference, the steeper the gradient and the faster they move, as when a drop of ink spreads in water. ## Related concepts - [Osmosis](https://studyvisually.com/learn/science/biology-school/biology-school-part-2/biology-school-part-2-concept-2) - [Active transport](https://studyvisually.com/learn/science/biology-school/biology-school-part-2/biology-school-part-2-concept-3) Web page: https://studyvisually.com/learn/science/biology-school/biology-school-part-2/biology-school-part-2-concept-1 Study this card in the app: https://studyvisually.com/app/learn?category=biology-school&card=biology-school-part-2-concept-1