Homeostasis Ms. Cuthrell

1.2.1 Explain how homeostasis is maintained in the cell and within an organism in various environments (including temperature and pH).

Homeostasis Homeostasis is a state of maintaining an internal balance within cells. Cells use buffers to regulate cell pH. Cells respond to maintain temperature, glucose levels, and water balance.

Plasma Membrane The plasma membrane is responsible for maintaining homeostasis.

1. Passive Transport Requires no energy to move across a membrane. Goes with the concentration gradient.

Diffusion The movement of a substance from an area of high concentration to an area of low concentration.

Osmosis Diffusion of water across a selectively permeable membrane.

Scenario 1 If the concentration of substances in the solution is the same as inside the cell. Water constantly moves in and out of the cell. No shape change. Equilibrium is reached.

Scenario 2 Higher concentration inside the cell. Water moves IN the cell in attempt to reduce the concentration- swelling Animal cells may burst if too much water comes in! Called lysis. Plant cells will only become more and more firm.

Scenario 3 Higher concentration outside the cell than inside. Water will move OUT in attempt to reduce the outside concentration. Cells will shrivel and shrink. Plants will wilt. Ex: When you put salt on a slug, it shrinks and dies.

2. Active Transport Requires energy. Uses the carrier proteins to change shape in order pass a particle. Substances can either go with or against the concentration gradient. Examples- Endocytosis, exocytosis, Sodium-Potassium Pump

Facilitated Diffusion Type of passive or active transport across a membrane with using a transport protein.