3.4 Diffusion and Osmosis KEY CONCEPT Materials move across membranes because of concentration differences.
3.4 Diffusion and Osmosis Solution: A homogenous mixture of two or more substances, which may be solids, liquids, or gases, or the combination of these. Ex: Sugar water Solute: Substance dissolved in another substance Ex: Sugar Solvent: Substance doing the dissolving (usually the substance present in the greatest amount) Ex: Water (THE BEST SOLVENT)
3.4 Diffusion and Osmosis Passive transport- the movement of molecules across a cell membrane without energy input from the cell There are two types of passive transport. 1. diffusion 2. osmosis
3.4 Diffusion and Osmosis Diffusion: is the movement of molecules in a fluid or gas from a region of higher concentration to a region of lower concentration.
Concentration gradient- the difference in the concentration of a substance from one location to another. Molecules diffuse down their concentration gradient Top ¼ pg. 30
3.4 Diffusion and Osmosis Osmosis is the diffusion of water molecules across a semipermeable membrane.
3.4 Diffusion and Osmosis Diffusion and osmosis are types of passive transport. There are three types of solutions. isotonic hypertonic hypotonic
Diffusion and Osmosis In terms of the solution: Hypertonic: When the solution is more concentrated than what’s inside the cell. This means water moves out to try and even out the concentration gradient. (The cell shrinks..i.e your fingers in the bathtub) Hypotonic: When the concentration is less concentrated than what’s inside the cell the water moves in to try and even out the concentration gradient. (The cell bursts or “lyses”.) Isotonic: When the concentration inside the cell is equal to that outside. Cell’s size remains constant.
3.4 Diffusion and Osmosis Some molecules cannot easily diffuse across the cell membrane Ex: H2O Facilitated diffusion is diffusion through transport proteins Things like H2O would be repelled by the phospholipid tails, so transport proteins allow the H2O to diffuse easily