1. Membrane Structure and Function
AP Biology
Chapter 7 (Part)

2. Passive Transport
Passive transport- the movement of materials across the cell membrane without using energy
All living cells live in a liquid environment.

3. Passive Transport
Diffusion: the process by which solute particles move from an area of high concentration to an area of lower concentration.
Solution  Solute + solvent
Concentration  amount of substance in a given volume

4. Passive Transport Diffusion Down concentration gradient
From higher concentration to lower concentration
Affected by size (more you have, the longer it takes)

5. Simple Diffusion
Suppose a substance is present in unequal concentrations on either side of a cell membrane.

6. Simple Diffusion
If the substance can cross the cell membrane, its particles will tend to move toward the area where it is less concentrated until it is evenly distributed.

7. Simple Diffusion
At that point, the concentration of the substance on both sides of the cell membrane is the same, and equilibrium is reached.

8. Simple Diffusion
Even when equilibrium is reached, particles of a solution will continue to move across the membrane in both directions.
Because almost equal numbers of particles move in each direction, there is no net change in the concentration on either side.

9. Passive Transport Summary
Diffusion is the tendency of molecules of any substance to spread out in the available space.
Diffusion is driven by kinetic energy (thermal motion or heat) of molecules.
In the absence of other forces, a substance will diffuse from where it is more concentrated to where it is less concentrated, down its concentration gradient.
Diffusion is a spontaneous process that increases entropy by creating a randomized mixture.

11. Osmosis: An Example of Diffusion
OSMOSIS: the movement of water through cell membranes
extremely important process
movement of water molecules from an area of higher concentration to an area of lower concentration

13. Osmosis Definitions
Differences in the relative concentration of dissolved materials in two solutions can lead to the movement of ions from one to the other.
Solution with higher concentration of solutes is hypertonic relative to the other solution.
Solution with the lower concentration of solutes is hypotonic relative to the other solution.
Solutions with equal solute concentrations are isotonic.

15. Movement of Water
Hypertonic solution will have relatively less free water than a hypotonic solution
The direction of osmosis is determined only by a difference in total solute concentration.
The kinds of solutes in the solutions do not matter.
When two solutions are isotonic, water molecules move at equal rates from one to the other, with no net osmosis.