1. 3.4 Diffusion and Osmosis
KEY CONCEPT Materials move across membranes because of concentration differences.

2. 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. 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

4. 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.

5. 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

6. 3.4 Diffusion and Osmosis
Osmosis is the diffusion of water molecules across a semipermeable membrane.

7. 3.4 Diffusion and Osmosis
Diffusion and osmosis are types of passive transport.
There are three types of solutions.
isotonic
hypertonic
hypotonic

8. 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.

9. 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