In lab 3, we examined many nutritional factors that can influence microbial growth. In this lab, you will continue this exploration by examining growth in even more environmental conditions. The rate of growth or death of a particular microbial species is influenced by a variety of physical factors in its environment including temperature, osmotic pressure, pH, and oxygen concentration. In nature, where many species coexist, fluctuating environmental conditions cause dramatic population shifts due to the varying growth rates of different microorganisms. Every microbial species has a set of optimal conditions under which it flourishes. However, because the conditions in natural environments fluctuate widely, microbes have adapted tolerance to a range of environmental conditions. For example, many microbes have an optimum growth temperature of 30°C, but will still grow, albeit slower, at 4°C. In the laboratory, where conditions can be controlled, it is possible to achieve optimal growth conditions for a given microorganism.