1. Chapter 5 Homeostasis and Cell Transport
Section 1 Passive Transport

2. Passive Transport
Substances cross the cell membrane without any input of energy
Ex. diffusion
Red dye diffusing into water

3. Diffusion
The movement of molecules from an area of high concentration to an area of lower concentration

4. Diffusion occurs until equilibrium is reached…
…the concentration of molecules is the same throughout a space

5. Diffusion Across Membranes
Called simple diffusion- cell membranes only allow certain substances to pass through
Cell membranes are semi-permeable

6. Materials that enter the cell through simple diffusion…
1) carbon dioxide
2) oxygen
Earthworms “breathe” through their skin!

7. Osmosis- a form of passive transport concerning water
The movement of water from an area of high concentration to an area of low concentration

8. The direction of osmosis…
Water moves out- cell shrivels
Water moves in-cells may burst
Same amt. of water moves in and out

9. What is the fate of the cell in each condition???
Isotonic-nothing; it’s normal
Hypertonic-shrivel/shrink
Hypotonic- burst

10. Hypotonic (Hippo-)
The cell gets bigger.

11. For red blood cells, this is fatal…
Hypotonic  isotonic  hypertonic

12. How Cells deal with Osmosis
For unicellular freshwater organisms, this is a problem. Some of them have special organs for removing water.
Ex. Paramecia have pumps called contractile vacuoles that constantly remove water from their bodies

13. Do the cells of this plant have turgor pressure?
Section 1 cont.
Turgor pressure- the pressure that water molecules exert against the cell wall
Do the cells of this plant have turgor pressure?

14. Plasymolysis- when a plant doesn’t receive enough water and the cell membrane shrinks from the cell wall; turgor pressure is not maintained

15. Facilitated Diffusion
A type of passive transport that is used for
1) molecules too large to pass through
the cell membrane
2) molecules that do not dissolve in lipids

16. Facilitated diffusion uses a carrier protein.

17. Facilitated Diffusion
What might this
molecule be?
Molecule attaches to protein.
Protein changes shape.
Molecule is released to other side.
Protein returns to original shape.

18. Ion Channels
Membrane proteins move Na+, K+, Ca+2, Cl- across the cell membrane

19. Three kinds of stimuli determine whether “gates” are open:
1) stretching of the cell membrane
2) electrical signals
3) chemical signals