1. Chapter 5 Homeostasis and Transport
Section 5.1

2. Passive Transport
The movement of substances across a cell membrane without any input of energy from the cell

3. Diffusion Simplest type of passive transport
Molecules move from an area of higher concentration to an area of lower concentration
Driven by kinetic energy

4. Equilibrium
When the concentration of the molecules of a substance are the same throughout a space

5. Diffusion Across Membranes
Cell membranes allow some molecules to pass through, but not others
Depends on size and type of molecule
Also depends on the chemical nature of the membrane

6. Osmosis
Water molecules diffuse across a cell membrane from an area of higher concentration of H2O to an area of lower concentration

7. Direction of Osmosis
Hypotonic- the concentration of solute molecules outside the cell is LOWER than the inside of the cell
Water moves INTO the cell

8. Hypertonic- the concentration of solute molecules outside the cell is HIGHER than the inside of the cell
Water moves OUT OF the cell

9. Isotonic- the concentrations of solutes outside and inside the cell are equal
No movement of water occurs

10. How Cells Deal with Osmosis
Contractile vacuole- organelles to remove water
Turgor pressure- pressure of water against the cell wall
Plasmolysis- cells shrink away from cell walls

11. Facilitated Diffusion
The movement of molecules across a cell membrane through the use of carrier proteins
First, a carrier protein binds to a molecule on one side of the cell membrane

12. Second, the carrier protein changes shape shielding the molecule from the interior of the membrane
Finally, the molecule is released on the other side of the membrane

13. Diffusion Through Ion Channels
Ion channels provide small passages for ions to diffuse across the cell membrane
Channels may have “gates” that respond to stretching of the cell membrane, electrical signals, or chemicals in the cytosol

14. Ions such as Na+, K+, Ca2+, and Cl- are important for a variety of cell functions