1. Cell Membranes Osmosis and Diffusion

2. Functions of Membranes 1. Protect cell 2. Control incoming and outgoing substances 3. Maintain concentrations of various substances 4. Selectively permeable - allows some molecules in, others are kept out

3. Methods of Transport Across Membranes 1) Two types of Passive Transport (uses no energy to move substances) Diffusion – the moving of particles from areas of higher concentration to those of a lower concentration (no energy used; like going down a hill) Osmosis - diffusion of water across a membrane 2) Active Transport- requires energy to transport molecules against a concentration gradient (like up a hill)

4. Diffusion

5. Osmosis

6. Blood-Brain Barrier Allows some substances into the brain, but screens out toxins and bacteria Substances allowed to cross include: water, CO 2, Glucose, O 2, Amino Acids, Alcohol, and antihistamines. HIV and bacterial meningitis can cross the barrier.

7. Plant and Animal Cells put into various solutions

8. Questions: 1.Which picture represents the carrot in the plain water? Why? 2.Which picture represents the carrot in the salt water? Why? 3. How does the human body maintain homeostasis using diffusion? (Hint: think about what happens when you eat a whole bag of sunflower seeds?)

9. http://www.youtube.com/watch?v=AYNwy nwaALohttp://www.youtube.com/watch?v=AYNwy nwaALo