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- Endocytosis = bringing materials into the cell

- 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

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- energy used to move the molecules changes the shape of the carrier protein

- Meaning the molecule can only fit in on one side

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- Carrier proteins act as pumps

- 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

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- Use facilitated diffusion

- Two types of protein molecules involved

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

- Carrier proteins - Shaped for specific molecules

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- CO2 & O2 small enough to pass through membrane

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

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- Diffuse down the concentration gradient

- Through membrane into cell

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- Temperature = higher temp gives molecules more energy, diffusion rate increases

- 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

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- Movement of molecules produces kinetic energy which diffusion depends on.

- Passive process

- Higher to lower concentration

- continual movement

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- Cells need a supply of nutrients to survive

- Reactions produce waste products that must be removed

- Molecules need to enter & leave the cells