2. The Plasma Membrane and Homeostasis

3. Homeostasis – Maintaining a Balance

4. Homeostasis Keep the proper concentration of nutrients and water Eliminate wastes The plasma membrane is selectively permeable

5. Structure of a Cell Membrane

6. Structure of the Plasma Membrane Lipid bilayer –two sheets of phospholipids –Found around the cell, the nucleus, vacuoles, mitochondria, and chloroplasts. –Embedded with proteins –strengthened with cholesterol

7. What’s a Phospholipid?

8. Pair of fatty acid chains Phosphate group Attached to a glycerol backbone. Polar heads face out Nonpolar fatty acids face inside.

9. Cellular Transport - Passive

10. Passive transport – no energy is needed to move particles. Diffusion – particles move from an area of high concentration to an area of low concentration. Facilitated diffusion – embedded proteins act as tunnels allowing particles to “fall” through Continues until an equilibrium is reached.

11. Osmosis

12. Diffusion of water across a selectively permeable membrane. Occurs until water is balanced on both sides of the membrane. Water MovesCellSolution InHypertonicHypotonic outHypotonicHypertonic No NetIsotonic

13. What’s the Point??

14. Cell Concentrations Hypertonic solutions – more dissolved solute. Hypotonic solutions – less dissolved solute. Isotonic solutions – the same dissolved solute.

15. Overcoming Osmosis

16. Contractile vacuoles –expel excess water from bacterial cells that live in water. Turgor pressure –water pressure in a plant cell. –Loss of turgor pressure causes wilting (plasmolysis).

17. Cellular Transport - Active

19. Active transport – Energy is needed to move particles. – This is movement UP the concentration gradient From an area of low concentration to high concentration.

20. Cellular Transport Active transport – energy is needed to move particles. –Carrier proteins – embedded proteins change shape to open and close passages across the membrane. –Endocytosis – taking something into the cell. –Exocytosis – expelling something from the cell.