Cells need to be able to transport very small molecules at quick rates. It is also often necessary to have consistent molecule concentration though out a cell. As a cell expands, volume becomes so great that passive means of transport such as osmosis become inadequate. Even active means, including ion "pumps" in the cell membrane, are not able to take molecules over long distances. Cells can overcome this problem, but only to a certain degree. …showed first 75 words of 1374 total…

…showed last 75 words of 1374 total…amount of energy production from the glycolysis reaction without oxygen does give a small margin of life without oxygen. References Taiz, L. and Zeiger, E. 1991. Plant Physiology. NY: Benjamin/Cummings http://www.eurekalert.org/pub_releases/2004-07/uoc--prn072104.php Harley, P.C. and Sharkey, T.D. 1991. An improved model of C3 photosynthesis at high CO2: reversed O2 sensitivity explained by glycerate reentry into the chloroplast. Photosynthesis Research 27, 169-178. http://aob.oupjournals.org/cgi/content/full/89/7/841