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the effect of ethanol on the rate of anaerobic respiration

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Introduction

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 species of budding yeast. It is perhaps the most useful yeast owing to its use since ancient times in baking and brewing. 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 waxes of the cuticle). 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. ...read more.

Middle

sugar-yeast mixture when dropping out of the end of the capillary tube Accurate Stop clock To time the start of the reaction and the time intervals Accurate and easy to handle Goggles For eye protection The only way to protect the eyes Water bath To warm up the test tubes and increase the rate of respiration Easy to handle and low hazard Absolute ethanol It is the substrate It is easily available Alkaline phenolphthalein indicator To see the colour change Easily produced and harmless Distilled water To dilute the concentration of ethanol It is harmless and easily available Beaker Contains solutions Easy to use and is able to contain large amount of solution Fair test: All of these variables (including the controlled variables) will need to be controlled by me, and to be kept the same throughout the experiment in order to keep it fair and to get as accurate results as possible. The independent variable, in this experiment the concentration of ethanol, has to be changed other than that all the factors have to stay the same throughout the whole experiment. Variables: - Independent variable: the different concentrations of ethanol - Dependent variable will be the time taken for the mixture to decolourise Table to show the variables that must be controlled: Variable Why it must be controlled How it will be controlled Temperature of yeast and sugar and sugar-yeast-ethanol-phenolphthalein mixture If you increase the temperature you increase the rate of reaction. ...read more.

Conclusion

They could be a result of putting the yeast into the mixture not into the test tube last and the reaction would have started already. We could not put the yeast into all test tubes, which were in the water bath, at the same time and as a result our time in minutes is not as accurate as it could be. Further we had to make sure that the phenolphthalein was mixed throughout the whole test tube. A table to show some possible effects of limitations on the method limitation Error that may have resulted from the limitation Rank order of limitation with qualification Suggested improvement Justification for improvement Reading off the syringe falsely Incorrect results 4 Ask partner to have a look as well and read off at eye level The results would be more accurate Not stirring the yeast and sugar-ethanol-phenolphthalein-yeast mixture before using it Different enzyme concentrations in the yeast resulting in unreliable measurements 2 Make a list, ticking that you stirred the mixture every time before using There would be one enzyme concentration of yeast only No constant temperature Incorrect results 3 Keep temperature constant with using an electric radiator Temperature is a controlled variable and has to stay constant otherwise the rates of reaction will be faster Not being able to put the yeast into the sugar-ethanol-phenolphthalein mixtures at the same time Incorrect results 1 Doing on test tube at a time Yeast is the source of the enzyme. When it is put at different times into the test tube the time taken to decolourise will be different. ...read more.

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