Photosynthesis and Respiration of Sugars by Yeast

Photosynthesis is the process in which plants make sugar, which stores the energy from the sun into chemical energy. Respiration complements photosynthesis in that it converts the chemical energy made by photosynthesis into organic molecules that may be used by organisms. Two different experiments were performed to test the amount of oxygen gas present during photosynthesis and the rate of respiration of different sugars by yeast. In the first experiment we used an oxygen gas sensor, which measured the amount of oxygen gas made by a plant during photosynthesis and respiration in both the light and the dark after five minutes and then in increments of three minutes. We concluded that the rate of photosynthesis and respiration in the light is greater than that in the dark because more light was absorbed and at a much faster rate. In the second experiment, we tested the respiration of sugars by yeast by finding the respiration rate of glucose, sucrose, starch, lactose, as well as water as the control. We found that of the sugars that were tested, yeast is able to metabolize sucrose and lactose because of its elevated respiration rate. It is important to be able to understand the ability yeast has to transport certain foods into the cells to make use of certain food sources.

INTRODUCTION It is important to understand the processes of both photosynthesis and cellular respiration. The main purpose of the first experiment is to demonstrate the effects of available light on a plants ability to perform photosynthesis. Photosynthesis is the process by which a plant breaks down water, carbon dioxide, and light to produce sugar (glucose) and oxygen. This process is critical for the plant as it is the direct method by which the plant generates its biological energy, otherwise known as ATP. Chlorophyll is a key factor in absorbing light to start photosynthesis. While every photosynthetic organism has Chlorophyll A, which absorbs violet-red and reflects blue-green, some plants also contain chlorophyll B, which absorbs blue-orange and reflects yellow-green. For example, in a previous experiment it was shown that crpytochromes and phototropins generated more oxygen in photosynthesis when exposed to blue light, whereas phytochromes generated more oxygen in photosynthesis when exposed to red light (Hogewoning et al 2010). In this experiment, we compared the amount of oxygen gas in parts per thousand (ppt) produced by photosynthesis in both no light and ample light to determine the effects light has on photosynthesis. High light intensities during the summer months allow for deeper penetration of light in the leaves, which increases the rate of photosynthesis, whereas in the winter months the low light intensity slows down the rate of photosynthesis (Sarlikoti et al 2011). This leads us to hypothesize that photosynthesis would only occur in the light. The main purpose of the second experiment is to demonstrate the ability of yeast to respire various sugars. In this experiment, we recorded the respiration rate for glucose, sucrose, starch, and lactose. There are two forms of cellular respiration: aerobic and anaerobic. Aerobic respiration requires oxygen as a reactant while anaerobic respiration does not require oxygen to carry out the process of respiration. This particular experiment deals aerobic respiration as it does require oxygen. Carbohydrates, fats, and proteins can all be consumed and processed as fuel for respiration, however glucose is the driving fuel for most cells (Reece et al 2011). Due to the fact that respiration requires glucose as an oxidizing agent for all living organisms, and that sucrose is a chemical combination of glucose and fructose, this leads us to hypothesize that the respiration rate of glucose and sucrose should metabolize faster than starch and lactose because they already contain all of the required elements for the first stage of