Chap. 5: Homeostasis and the Cell Membrane

1. Chap. 5: Homeostasis and the Cell Membrane --- Homeostasis – steady state of balance between a cell and its environment.

2. I. Types of Membranes • 1. Selectively (Semi) Permeable – decides what will enter or exit the cell. (What cell membrane is most of the time) • 2. Permeable – allows everything in or out of cell. • 3. Impermeable – does not allow anything in or out of cell.

3. II. How a Selectively (Semi) Permeable Membrane Selects What Enters or Exits • 1. Size of Particle – small do (water, glucose, ions, etc) and large do not. • 2. Chemical makeup – if water then automatically does and anything dissolved in it (sugar, salt, ions) • 3.What conditions are inside and outside the cell --- Diffusion and Osmosis

4. III. Diffusion and Osmosis • -- diffusion – moving of particles from high concentration to low concentration. Requires no energy • -- osmosis – diffusion of only water • -- solute – substance being dissolved (smaller quantity) • -- solvent – substance being dissolved into (larger quantity)

5. IV. Types of Solutions 1. Hypertonic Solution – solute concentration is greater outside than inside so WATER rushes out. Result : Causes Plasmolysis – cell shrinking. Common in salt water that is why skin shrivels up

6. 2.Hypotonic Solution – solute concentration is greater inside than outside so WATER rushes in. Result : cell swelling which may result in Cytolysis (cell rupture). One-celled organisms(i.eameoba, paramecium) that live in a water environment have ContractileVacuoles to pump water out.

7. 3. Isotonic Solution – solute concentration is the same inside and outside. • Result : little or no movement of WATER into or out of the cell.

8. *** In Plant Cells : Because they have a cell wall there are slight differences. • Hypertonic solution – causes cells to be limp (decreases turgor pressure) • Hypotonic solution – causes cells to be stiff (decreases turgor pressure )

9. V. Types of Transport 1. Passive Transport – Does not require energy. Follows concentration gradient (high to low) a. osmosis b. diffusion c. facilitated diffusion – carrier molecules (proteins) speed up the diffusion process

10. d. Gated channels – channels in cell membrane that specifically allow some molecules to pass through that are not usually permeable to the membrane

11. 2. Active Transport – requires energy by cell to take place A. contractile vacuoles B. sodium – potassium pumps (Na+--K+) – causes electrical charges to travel across cells which lead to muscular contractions and neurons firing. Must go against a concentration gradient. Pumps 3Na+ out and 2 K+ pumped in.

12. c. Endocytosis – the entering of large molecules into the cell. (lipids, fats, polysaccharides, etc.) -- pinocytosis – (cell drinking)- movement of large molecules of fluid and/or ions into cell. -- phagocytosis – (cell eating) – movement of food molecules into cell.

13. d. Exocytosis - exiting of large molecules out of the cell.