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

2. 3.4 Diffusion and Osmosis A concentration gradient is the
difference in the concentration
of a substance from one location
to another.
Molecules diffuse down a concentration
gradient, which means that they move
from an area of higher concentration
to an area of lower concentration, until
equilibrium is reached (same amount
of molecules on both sides of the cell
membrane).

3. 3.4 Diffusion and Osmosis
Passive transport is the movement of molecules across a cell membrane without energy input from the cell.
There are two types of passive transport:
Diffusion – the movement of molecules in a fluid or a gas from a region of higher concentration to a region of lower concentration
Osmosis – the movement of water molecules from a region of higher concentration to a region of lower concentration

4. 3.4 Diffusion and Osmosis
Diffusion and osmosis are types of passive transport.
There are three types of solutions.
isotonic
hypertonic
hypotonic

5. 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.