Cell Membrane Structure and Function
1. Define:
Plasma membrane - an invisible surface layer that surrounds and limits a cell. This layer is very thin so is not visible with a light microscope. It is dynamic (ever changing) and is selectively and differentially permeable. It controls what enters and exits the cell.
Amphipathic (amphiphilic) - molecules that have both polar ( hydrophilic) and non-polar (hydrophobic) parts in their structure. The phospholipids and many of the proteins associated with cell membranes have this characteristic.
Diffusion - the movement of particles to fill an available space. The particles may be liquid, solid or gas, and move passively due to random molecular activity. Net movement is from an area of high concentration to areas of lower concentration. Diffusion does not require a membrane, but may occur across a membrane.
Exocytosis - the process by which large particles (macromolecules) contained within membranous vesicles, may exit a eukaryotic cell. This transport process requires energy or work on the part of the cell. It may also be called emiocytosis or cell vomiting.
Phototaxis - the movement of a cell through it's environment that is directed by light. (Taxis=directed movement). Phototaxis involves light sensitive receptors in the cell membrane. The movement may be directed toward light (positive phototaxis) or away from light (negative phototaxis).
2. plasma membrane or cell membrane/ lipid/ protein
3. integral or intrinsic/ Na+, K+, H+, etc./ facilitated diffusion
4. phospholipids/ fatty acid
5. simple diffusion/ concentration
6. osmosis/ hypertonic
7. gain or take in
8. concentration and/or electrical
9. antiport
10. Facilitated diffusion allows particles to move down their concentration and/or electrical gradients, while active transport can be used to move particles "uphill" or against their concentration and/or electrical gradients. Facilitated diffusion is a passive process, while active transport requires the cell to expend energy.
11. phagocytosis (endocytosis involving large particles)/ pinocytosis (endocytosis involving molecular sized particles - not visible with a light microscope).
12. positive chemotaxis
13. negative phototaxis
14. cholesterol/ ATP
Copyright 2002 Sierra College Biological Sciences Department
Last updated: 01/18/02.
