Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach. This Science Object, co-developed between FDA and NSTA, second of four Science Objects in the Food Science Safety SciPack. It explores cell functions involving chemical reactions that are made possible by protein catalysts called enzymes. These reactions require a fairly narrow range of temperature and pH. Low temperatures cause them to go too slowly, and high temperatures or acidity can change cell structures. Molecules from the environment may also attach to or pass through a cell's membrane and affect reaction rates. Cells such as bacteria require energy and nutrients from their environment for survival. When they grow to a certain size, bacteria can reproduce by creating a copy of their DNA and then splitting in two. Under optimal conditions, this doubling of bacteria and each of their generated offspring can proceed at a fast rate, expanding a bacterial colony rapidly in a short time. Many of the precautions taken to protect the health of humans focus on limiting the growth of bacterial colonies by creating environmental conditions not favorable for their functioning or reproduction. Variations in genetic information within a population of bacteria can permit some individuals to survive and reproduce more effectively than others in a given environment. Such hardier individuals usually represent only tiny fractions of a population, but their rapid reproduction can quickly give rise to large numbers of successful offspring. This process may give rise to bacterial strains able to survive under new conditions, such as strains with resistance to overused antibacterial drugs, or grant previously harmless bacteria the ability to cause disease.