4 A Membranes 1 Membranes 1 Membranes Thin

4 A - Membranes

• 1. Membranes –

• 1. Membranes – – Thin covering that forms the outer boundary of a cell – Made of lipids (fats) and protein – Fluid Mosaic Model – lipids form a fluid (film) in which the proteins float around in. The proteins make patterns (mosaics) in the fluid.

• 2. Membranes are selectively permeable. – Selectively permeable means that certain molecules can go through the membranes while others can not. – Different membranes let different substances pass through them. For example some may allow sugar to pass through, while others do not.

• 3. There are two ways that substances can pass through a membrane. – Passive Transport – Active Transport

• 4. Passive Transport –

• 4. Passive Transport – – Passive transport is one of the ways that substances can pass through a membrane. – The cell does NOT use its own energy with passive transport. – Two types of passive transport: • Diffusion and Osmosis

• 5. Diffusion –

• 5. Diffusion – – One type of passive transport – Diffusion – movement of molecules from a place where there are many of them to a place where there are few of them. – Examples: Spray air freshener, Kool-Aid mix in water.

• 6. Osmosis –

• 6. Osmosis – – One type of passive transport – Osmosis is the diffusion of water through a membrane. – Example – stentor pg. 68

• 7. Active Transport – – One way substances move through a membrane. – Cells use own energy to move substances.