Diffusion

Diffusion is the movement of molecules from areas of High Concentration to areas of Low Concentration. Basically, it means molecules tend to spread out if they can.

Brownian Motion is the random movement of particles in a liquid or gas.
Objects in motion will stay in motion unless acted on by an outside force.
If molecules are crowded together, they will bounce off of each other; if their path takes them away from the other molecules, then they will stay on it. Thus, they tend to move to places with fewer molecules.
Osmosis is the diffusion of water across a membrane

Diffusion

Diffusion is the most important method of transport in cells/organisms.

Cell membranes have channel proteins that are like little tunnels that let certain molecules pass through because they are already moving.
Diffusion does not require the cell to use ATP to transport molecules (Passive Transport).
To increase diffusion, cells/organisms need to increase the surface area that is exposed to the molecules.
- Lungs have millions of tiny pockets (alveoli) that allow us to bring in much more oxygen than if our lungs were shaped like balloons.
- Intestines have millions of tiny projections called villi (think of it like shag carpet) that stick out and allow you to absorb more nutrients from your food.

Osmosis

Osmosis is the diffusion of water across a membrane.

It is important for keeping cells/organisms properly hydrated.
- Too much water and they can pop
- Too little water and they can dry out
As long as membranes are permeable to water, osmosis is controlled by solutions on either side of the membrane.
- Solute - the substance dissolved in the solvent
- Solvent - the liquid that dissolves the solute (usually water)
- Hypertonic Solution - one that has a high concentration of solute (low water)
- Hypotonic Solution - one that has a low concentration of solute (high water)
Most membranes are Selectively Permeable - they "choose" what molecules are able to pass through.
- Often, water can pass through, but solutes cannot.
- Water moves from Hypotonic solutions to Hypertonic solutions.