3.4 Diffusion and Osmosis

1. 3.4 Diffusion and Osmosis • LEQ: How does passive transport move chemicals across a cell membrane? • Reading: 3.5, 3.2 (focus on organelles with membranes) • Quiz friday • Journal: • Think of several features and parts of membranes necessary for them to function correctly and then write an entry detailing how changing them could cause a membrane to function poorly. • Key terms – diffusion, osmosis, passive transport

2. 3.4 Diffusion and Osmosis Diffusion is the random movement of particles in a solution. • All molecules and atoms are in constant motion: • Energy • Collision • Heat (thermal energy) • Diffusion applet (see screen) • 3 general types of passive transport:

3. Journal prompt: Have you ever been stuck in crowd? A cramped elevator or a packed concert can cause certain responses in people. Describe how people might feel in a crowded space. • Construct an analogy to explain why molecules diffuse from high to low concentrations using crowds.

4. 3.4 Diffusion and Osmosis Materials move across membranes because of concentration differences. • Passive Transport: • Powered by random atomic & molecular movement • No energy requirements

5. 3.4 Diffusion and Osmosis 1) Some chemicals can move across the cell membrane by simple diffusion. • Diffusion gradients: • Differences in concentration • Net movement: • high  low • small, nonpolar solutes: • O2, CO2, steroids

6. 3.4 Diffusion and Osmosis 2) Many solutes can only pass across a membrane through facilitated diffusion. • Facilitated diffusion moves chemicals through specialized transport proteins • Small or large • Polar, Ionic • Regulation • Size/shape restricted • gates

7. 3.4 Diffusion and Osmosis • 3) Osmosis is the net movement of water in response to solute concentrations and pressure • Cells are sensitive to changes in solutions • Water diffuses down concentration gradients • Weakly via simple diffusion • Facilitated • aquaporins

8. 3.4 Diffusion and Osmosis • normalcy for animal cells • equilibrium • Crenation (wrinkling) • dysfunctional • expansion • cell death (lysis)

9. Summary • Explain what a concentration gradient is and what it means for a molecule to diffuse down its concentration gradient • Explain why facilitated diffusion does not require energy from a cell • A cell is bathed in fluid. However, you notice that water is flowing out of the cell. In what kind of solution is this cell immersed: isotonic, hypotonic, or hypertonic? • How are receptors and transport proteins similar?

10. Answers • A concentration gradient is the difference in concentration of a substance from one location to another. A molecule diffuses down its concentration gradient by moving from one region of higher concentration to a region of lower concentration. • No energy is needed because the molecules move down an concentration gradient • Hypertonic • Both are proteins and may work with only specific molecules. In addition, both may require a change in shape to accomplish their function.