2 Difference between active and passive transport Cells maintain homeostasis by controlling the movement of substances across their cell membrane.No energy needed = passive transportEnergy needed = active transport
3 Passive TransportDifferences in concentration = concentration gradientConcentration is the same all through = EquilibriumPassive transport can happen when there is a concentration gradientMolecules in equilibrium continue to move but the movement is equal in all directions
4 Diffusion – the most common form of passive transport Molecules move from an area of high concentration to an area of lower concentrationMany substances enter or leave cells by diffusing across the cell membrane.
6 Osmosis – a special type of diffusion The diffusion of water through a selectively permeable membrane = osmosis.Water goes into or out of a cell by osmosis
7 Osmosis, continuedThere are three possibilities for the direction of water movement:Water moves out - the cell shrinks. A solution that causes a cell to shrink is a hypertonic solutionWater moves in - the cell swells. A solution that causes a cell to swell is a hypotonic solutionEqual water movement – the cell stays the same. A solution that produces no change in cell volume is an isotonic solution
9 Other forms of passive transport 1. Diffusion Through Ion ChannelsA transport protein with a pore through which ions can pass.An ion can cross the cell membrane without touching the interior of the lipid bilayer.
11 Other forms of passive transport, continued 2. Facilitated DiffusionCarrier proteins - can bind to a substance on one side of the cell membrane, carry the substance across the cell membrane, and release it on the other side.