Substances cross cell membranes via diffusion (high to low concentration), facilitated diffusion (with proteins), osmosis (water), or active transport (low to high concentration, requiring proteins and energy). Small, non-polar molecules pass through the lipid bilayer, while larger, polar molecules use proteins.
Substances cross cell membranes via diffusion (high to low concentration), facilitated diffusion (with proteins), osmosis (water), or active transport (low to high concentration, requiring proteins and energy). Small, non-polar molecules pass through the lipid bilayer, while larger, polar molecules use proteins.
| Front | Many different substances enter and leave a cell by crossing its cell surface membrane. Describe how substances can cross a cell surface membrane. ( 5 marks) |
|---|---|
| Back | (Simple/facilitated) diffusion from high to low concentration/down concentration gradient; Small / non-polar / lipid-soluble molecules pass via phospholipids / bilayer; Large / polar / water-soluble molecules go through proteins; Water moves by osmosis/from high water potential to low water potential/from less to more negative water potential; Active transport is movement from low to high concentration /against concentration gradient; Active transport/facilitated diffusion involves proteins/carriers; Active transport requires energy/ATP; Ref. to Na+ /glucose co-transport; |
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