Yeast Culture Lab
I. Introduction
1. Yeasts are eukaryotic, unicellular fungi that inhabit liquid or moist habitats. They are heterotrophs and rely on complex organic substances for nutrition. Yeasts require oxygen for aerobic cellular respiration but some are also anaerobic with alternative aerobic methods for producing energy. They do not require light to grow and their temperature range varies which means they can survive in a multitude of different environments. Very common, they can be found anywhere, from occurring on the skins of fruits to residing in the intestinal tracts of animals as parasites. The most common method of reproduction for yeasts is asexual reproduction through budding. In this process, the parent cell’s nucleus splits and forms a daughter nucleus. The daughter cell grows on the parent cell until it is large enough to separate. Through cytokinesis, this ‘bud’ then forms a new cell. Less common is the method of sexual reproduction in which spores are formed. In this lab, I will be culturing four yeast samples under different conditions. The goal is to study the effects of limited reproduction, additional resources (nutrition) and predation on the yeast population. Yeasts play a very important role not only by serving as nutrient recyclers in nature, but by also being important for the food industry because they can convert carbohydrates to carbon dioxide and alcohols through fermentation. They are also used in cell biology research and produce ethanol.
2. When ammonia, which limits reproduction, and a microbe (predation) are added to the culture, the yeast population will decrease. And when additional food is introduced into the environment, the yeast population will increase considerably, but then stabilize because of the carrying capacity of the environment. In all four groups, the yeast population will decline in the end because food