Chap. 5: Homeostasis and the Cell

Membrane

--- Homeostasis – steady state of balance between a cell and its environment.

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.

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

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 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

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 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

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.