Diffusion

• Diffusion is the gradual movement of particles from places where there are lots of them to places where there are fewer of them - it’s just the natural tendency for stuff to spread out.
• Diffusion is the spreading out of particles from an area of higher concentration to an area of lower concentration.
• The simplest type of diffusion is when gases diffuse through each other. This is what’s happening when the smell of perfume diffuses through the air in a room.
• In diffusion, the bigger the concentration gradient (the difference in concentration), the faster the diffusion rate.
• In diffusion, a higher temperature will give a faster diffusion rate because they particles have more energy so move around faster.
• Cell membranes hold the cell together but they let stuff in and out as well.
• Dissolved substances can move in and out of cells by diffusion. Only very small molecules can diffuse through cell membranes though - things like oxygen (needed for respiration), glucose, amino acids and water.
• Big molecules like starch and proteins can’t fit through cell membranes.
• Just like diffusion with air, particles flow through cell membranes from where there‘s a higher concentration (a lot of them) to where there‘s a lower concentration (not such a lot of them).
• In diffusion through cell membranes, the particles are moving about randomly so they go both ways - but if there are a lot more particles on one side of the membrane, there‘s a net (overall) movement from that side.
• In diffusion through cell membranes, the larger the surface area of the membrane, the faster the diffusion rate because more particles can pass through at once.