The effect of ethanol on the rate of anaerobic respiration of glucose by yeast
Aim:
This is an experiment to investigate the six different ethanol concentrations on the time for the mixture containing glucose, yeast, ethanol an alkaline phenolphthalein to decolourise.
Background theory:
Saccharomyces cerevisiae is a of . It is perhaps the most useful owing to its use since ancient times in and . It is believed that it was originally isolated from the skins of grapes (one can see the yeast as a component of the thin white film on the skins of some dark-colored fruits such as plums; it exists among the of the ).
Glucose molecules contain energy. The energy in glucose originally came from sunlight which was captured by chlorophyll molecules and used to make glucose in photosynthesis. If glucose is placed in oxygen and set alight, it burns vigorously. Large amounts of heat energy are released as the glucose molecules combine with oxygen to form carbon dioxide and water, and the energy from the glucose is rapidly transferred to heat energy. As this oxygen comes from the air, the process is called aerobic respiration.
When oxygen isn’t available, oxidative phosphorylation and the Krebs cycle cannot take place. This is also true in organisms or cells which do not contain the machinery to carry these out. In these circumstances, respiration takes place without oxygen- anaerobic respiration. In anaerobic respiration, glycolysis takes place as usual, producing pyruvate and a small yield of 2 ATP.
Glycolysis is the lysis of glucose. It is a multi- step process in which a glucose molecule with six carbons is broken down into two molecules of pyruvate, each with three carbon atoms. Energy from ATP is needed in the first steps, but energy is released in later steps, when it can be used to make ATP. There is a net gain of two ATP molecules per molecules of glucose broken down. Glycolysis takes place in the cytoplasm of the cell. In the first stage, phosphorylation, glucose is phosphorylated using ATP. As glucose is energy- rich, but doesn’t react easily energy must first be used to make the reaction easier. Two ATP molecules are used for each molecule of glucose to make hexose biphosphate, which breaks down to produce two molecules of triose phosphate. Hydrogen is then removed from triose phosphate and transferred to the carrier molecule NAD (nicotinamide adenine dinucleotide). Two molecules of NAD are produced for each glucose molecule entering glycolysis. The hydrogen carried by the reduced NAD can easily be transferred to other molecules and are used in oxidative phosphorylation to generate ATP.
