what is diffusion? - diffusion is movement of particles from a high to low concentration and is a passive process , does the substance have to be soluble in order to diffuse through the semi-permeable membrane? - Yes, give 3 examples of soluble substances - steroid hormones, Oxygen, Carbon Dioxide , give 3 examples of insoluble substances - Glucose, proteins, lipids , what 4 factors affect diffusion? - temperature (kinetic energy), distance, surface area, thickness of membrane , What is facilitated diffusion? - passive process where specific protein carriers and channels are used , What particles are transported by facilitated diffusion and why? - charged particles and polar charged particles because large particles are too big to cross the membrane by facilitated diffusion , What is co-transport - where two different molecules are transported by same carrier protein, Give an example of co-transport - glucose and sodium , Why two proteins are utilised in facilitated diffusion? - Carrier proteins and Channel proteins , What are channel proteins and what do they do? - They consist of pores lined with polar groups (hydrophilic). This allows charged ions to pass through . Each channel is specific for one type on ion and can open and close depending on needs of cell , What do carrier proteins do? - Allow facilitated diffusion of large polar molecules across the membrane. A particular molecule attaches to a carrier protein at the binding site, changing its shape or causing a rotation in the membrane which releases the molecule on the other side of the membrane , What is the process of facilitated diffusion?, What is happening at point X - the sodium ions and glucose are attached to the carrier protein which changes shape and deposits and leaves the sodium and glucose in the cell , What is happening at point Y - The glucose and sodium diffuse separately so at Y the sodium is pumped out of the epithelial cells by active transport and therefore maintains the concentration gradient needed for sodium to diffuse from the gut lumen to the cells , What is happening at point Z - Glucose leaves the epithelial tissue at Z by facilitated diffusion ,

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