- Reactions produce waste products that must be removed

- Molecules need to enter & leave the cells

- Passive process

- Higher to lower concentration

- continual movement

- Concentration gradient

- Agitation = increases movement, diffusion rate increases

- Surface area = more surface area, more area for diffusion, diffusion rate increases

- Distance/thickness = thicker distance, longer diffusion takes, diffusion rate decreases

- Size of molecule = smaller molecules, diffusion rate increases

- Through membrane into cell

- Water molecules are very small, pass straight through despite being polar

- Two types of protein molecules involved

- Channel proteins - form pores in the membrane, gated (open & close)

- Carrier proteins - Shaped for specific molecules

- they are complementary to the molecules they carry

- Carries large/charged molecules

- moves molecules one way

- uses metabolic energy (ATP)

- opposite direction to concentration gradient

- Faster rate of movement than diffusion

- Molecules can be accumulated either inside cells or organelles, or outside cells

- Meaning the molecule can only fit in on one side

- Exocytosis = moving material out of the cell

- Bulk transport is possible because membranes can easily fuse, separate and 'pinch off'

- Require energy from ATP, used to form vesicles