Yeast (Saccharomyces)is a single-celled microorganism in the Fungi family. It anaerobically respires sugars to produce ATP, as well as the waste products ethanol and carbon dioxide gas. This process is known as fermentation. There are various factors that affect the rate at which yeast respires. Aim
To investigate the effect of concentration of table salt (sodium chloride) on the rate of fermentation of sucrose using yeast, measured in the volume of carbon dioxide gas collected over a period of 10 minutes. Research question
What is the effect of concentration of table salt on rate of fermentation? Hypothesis
I predict that as salt concentration is increased, the rate of fermentation will decrease. Yeast cells do not have a cell wall and therefore, due to osmosis, a higher salt concentration outside the yeast cells will provide them with a hypertonic environment. This will cause water to move from the yeast cell to its surroundings, down the concentration gradient. Thus the yeast cells will become dehydrated, cannot function properly and eventually die. Low salt concentrations, however, will not have significant effect on yeast respiration as the concentration gradient will not be great enough to dehydrate the yeast cells. Therefore, the graph would start out flat and then slope downwards at an increasingly steep gradient, finally reaching zero. Variables
Independent: the concentration of salt in a mixture of sucrose, yeast and water. Dependent: the rate of fermentation of sugar using yeast, measured by the volume of carbon dioxide produced in ten minutes. Control:
* Concentration of yeast – more yeast (higher concentration) will increase rate of fermentation, as there is a greater number of yeast-enzymes available to respire the sugar. * Concentration of sugar – more sugar (higher concentration) will increase rate of fermentation, as there is more substance available for the yeast to...