Diffusion

• Diffusion is the movement of particles from an area of high concentration to an area of low concentration through a semi-permeable membrane
• High to low
• go down a concentration gradient
• Diffusion will happen faster if the gradient is steeper
• A higher temperature = more kinetic energy = diffusion happens quicker
• Semi-permeable membrane = selective; only small molecules can enter
• Rules of explaining = TYPE OF PROCESS; DEFINITION OF PROCESS; SPM; IN/OUT
• Visking Tubing is a model of a semi-permeable membrane
• Large molecules cannot pass through a semi-permeable membrane
• If there is glucose and starch in a visking tubing, after 30 minutes only the glucose will have diffused as it is small enough to pass through the semi-permeable membrane. BUT the starch is a large molecule so will not be able to diffuse and stays in the visking tubing.
• We use iodine to test for starch, turning inky blue-black if positive
• We use heated benedict's solution to test for glucose, turning brick-red if positive