Homeostasis and the Plasma Membrane BIOLOGY Maintaining Balance

Homeostasis and the Plasma Membrane BIOLOGY

Maintaining Balance • Living cells maintain a balance by controlling materials that enter and leave. • The Plasma Membrane maintains homeostasis by allowing only certain particles to pass through, this ability is known as: • Selective Permeability

Structure of the Plasma Membrane • Lipid Bi-layer - Two layers of phospholipids • Phospholipid - two fatty acids and a phosphate group, attached to a glycerol ‘backbone’.

Structure of the Plasma Membrane • Phosphate heads are polar, they are attracted to water which causes them to line up with the heads pointing in opposite directions.

Structure of the Plasma Membrane • Phospholipid molecules are able to move sideways within the membrane - fluid mosaic model.

Cholesterol • Cholesterol molecules are rigid. • They strengthen the fluid mosaic and make it more stable. • Help keep the fatty acid tails of the phospholipids separated.

Protein • Made of: • Used as:

Proteins • Doorways for the membrane. • Allow certain particles to pass through. • Serve as markers, enzymes, communicatons centers.

Bibliography • Biology The Dynamics of Life, Biggs, Kapicka, Lundgren, Glencoe/Mc. Graw-Hill, 1995 • www. class. unl. edu/bios 201/chapter 4 WEB/index. htm, Professor Steven D. Schwartzbach, 10/22/99 • www. ultranet. com/~jkimball/Biology. Pages/c? Cell. Membra nes. html, Cell Membranes, 5/21/99