Materials move across membranes because of concentration differences. 3.4 Diffusion and Osmosis Materials move across membranes because of concentration differences. High Concentration Low Concentration

Molecules can move across the cell membrane through passive transport. 3.4 Diffusion and Osmosis Molecules can move across the cell membrane through passive transport. Passive transport does not require energy input from a cell. There are two types of passive transport: diffusion osmosis

Diffusion Diffusion- movement of molecules from a region of higher concentration to a region of lower concentration

Molecules diffuse down a concentration gradient 3.4 Diffusion and Osmosis Concentration gradient is the difference in the concentration of a substance from one location to another Molecules diffuse down a concentration gradient

3.4 Diffusion and Osmosis Osmosis is the diffusion of water molecules across a semipermeable membrane.

Osmosis There are three types of solutions. tonic = pressure 1) isotonic 2) hypertonic 3) hypotonic

3.4 Diffusion and Osmosis Some molecules can only diffuse through transport proteins and cannot easily diffuse across the cell membrane. Facilitated diffusion is diffusion through transport proteins.

Facilitated Diffusion