1. Objective: 4(B) Investigate and explain cellular processes, including homeostasis, energy conversions, transport of molecules, and synthesis of new molecules.

4.  The process of maintaining balance in an organism’s internal environment is called homeostasis.  One of the structure responsible for homeostasis is the plasma membrane.  The Plasma membrane forms a thin, flexible boundary between a cell and its environment.

5.  Plasma membranes have selectively permeability, meaning they allow some substances to pass through while keeping others out.  Control of how, when, and how much of various substances enter and leave a cell depends on the structure of the plasma membrane.

6.  The plasma membrane is composed of a phospholipid bilayer – composed of phospholipid molecules arranged with polar heads facing the outside and nonpolar tails facing the inside.

7.  The phospholipid bilayer is polar on its surface and nonpolar in the middle.  The plasma membrane separates the internal and external environment.  Because water soluble substances will not move easily through due to the nonpolar middle.

8. Other Components of the Plasma Membrane  Proteins  Some are receptors that transmit signals to the inside of the cell.  Some serve as support structures for the membrane.  Some are transport proteins that move needed substances and wastes through the membrane.

9.  Cholesterol  Prevents the fatty acids tails of the phospholipid bilayer from sticking together.  Contributes the fluidity of the membrane.

10.  Carbohydrates  Define the cell’s characteristics.  Help cell identify chemical signals.

11.  The fluid mosaic model describes the bilayer as a “sea” in which other components can float and move around.  Different substance in the plasma membrane create a mosaic pattern on the surface of the cell.