Cell membranes

• Cell membranes hold the cell together but also let things in and out.
• Dissolved substances can move in and out by diffusion.
• Only very little molecules can diffuse through cell membranes such as oxygen, glucose, amino acids and water.
• Big molecules such as starch and proteins can't fir through the membrane.
• Just like diffusion in air, particles flow through the cell membrane from where there's a higher concentration to a lower concentration.
• The particles move randomly so they move both ways but if there is a lot more particles on one side of the membrane there's a net movement from that side.
• net movement means overall movement
• The larger the surface area of the membrane the faster the diffusion rate because the more particles that can move through at once.