Chap. 5: Homeostasis and the Cell Membrane

Chap. 5: Homeostasis and the Cell Membrane

Chap. 5: Homeostasis and the Cell Membrane--- Homeostasis steady state of balance between a cell and its environment.I. Types of Membranes1. 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.

II. How a Selectively (Semi) Permeable Membrane Selects What Enters or Exits1. 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

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)

IV. Types of Solutions1. 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

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.e ameoba, paramecium) that live in a water environment have Contractile Vacuoles to pump water out.

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

*** 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 (increases turgor pressure ). Solution plants prefer

V. Types of Transport1. 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

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

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.

c. Endocytosis the entering of large molecules into the cell. (lipids, proteins, 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.

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