chap. 5: homeostasis and the cell membrane --- homeostasis – steady state of balance between a...
TRANSCRIPT
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.