3.4 Diffusion and Osmosis KEY CONCEPT Materials move across membranes because of concentration differences.

3.4 Diffusion and Osmosis Passive transport does not require energy input from a cell. Molecules can move across the cell membrane through passive transport. There are three types of passive transport. Diffusion – the movement of molecules from a higher concentration to a lower concentration. Osmosis – the diffusion of water. Facilitated diffusion – the diffusion of molecules across a membrane through a transport protein.

3.4 Diffusion and Osmosis Diffusion and osmosis are types of passive transport. Molecules diffuse down/with a concentration gradient which is the difference in concentration of a substance from one location to another. This means molecules move from a region of higher concentration to a region of lower concentration. “Spreading out”

3.4 Diffusion and Osmosis Another example of diffusion is the gas exchange in our bodies. - O2 (oxygen) is higher in the lungs than in the blood, so O2 diffuses from the alveoli in the lungs to the blood. CO2 (carbon dioxide) moves from the blood to the lungs also by diffusing down its concentration gradient.

3.4 Diffusion and Osmosis Diffusion, osmosis and facilitated diffusion are types of passive transport. Osmosis is the diffusion of water molecules across a semipermeable membrane. Osmosis requires no energy to occur because osmosis happens with the concentration gradient.

3.4 Diffusion and Osmosis Examples of Osmosis: The absorption of WATER by plant roots - and - The absorption of WATER in the small intestine and colon use osmosis.

3.4 Diffusion and Osmosis Some molecules can only diffuse through transport proteins. Some molecules cannot easily diffuse across the cell membrane. Facilitated diffusion is diffusion through transport proteins. This process does not require energy. Facilitated diffusion usually occurs when molecules cannot directly pass through the membrane on their own due to the size of the molecule, charge or polarity.

Example of Facilitated Diffusion - Glucose 3.4 Diffusion and Osmosis Example of Facilitated Diffusion - Glucose

3.4 Diffusion and Osmosis Diffusion and osmosis are types of passive transport. There are three types of solutions. Isotonic – iso means “the same” Hypertonic – hyper means “over or too much” Hypotonic – hypo means “under or not enough”

Factors that affect rate of diffusion? Take some time to think about various factors that could affect the rate of diffusion. Which factors would increase the rate? Which factors would decrease the rate? Temperature Particle Size pH Solute concentration