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# The rate ofrespiration in yeast and how it is affected by temperature.

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Introduction

The rate of respiration in yeast and how it is affected by temperature Planning Introduction Yeast is a single celled, or unicellular, fungus made up mostly of protein. Once yeast is activated, it respires by secreting the enzyme zymase into the yeast, which acts on simple sugars such as glucose. This gives off carbon dioxide, energy and alcohol (such as ethanol) in anaerobic respiration or water, carbon dioxide and energy in aerobic respiration. The alcohol produced can be used to make wines and beers, and the carbon dioxide produced can be used in baking, as it gets trapped in the dough and causes it to rise. When the yeast respires, we say that respiration is occurring. Respiration is the process off getting energy from food. This occurs in every living cell. Yeast can respire both aerobically (with oxygen) and anaerobically (without oxygen). The equation for aerobic respiration is: Glucose + oxygen water + carbon dioxide + energy The equation for anaerobic respiration is: Glucose Alcohol + carbon dioxide + energy We are going to study the aerobic respiration of yeast. This is respiration with oxygen, as air containing oxygen will be present. This is an enzyme-controlled reaction. Enzymes only work up to a certain temperature, until they are denatured. This means that, in theory, the reaction will work best at certain conditions, but when the enzymes are denatured the reaction stops and is unable to go forward. Aim: The aim of my experiment is to discover if there is any correlation between rate of respiration of glucose by yeast and the temperature at which the reaction is taking place. Prediction: I predict that the rate of respiration of the yeast will increase as the temperature increases, up until a certain point where the enzyme used in this reaction is denatured. This is because at a certain temperature it becomes too hot for the enzymes to continue working, and once the temperature has reached this point the enzymes will never be able to work again - we say they have denatured. ...read more.

Middle

I placed the thin rubber tube on the end of the syringe. * I set up apparatus as shown in the diagram, making sure that no air is left in the smaller syringe - all of the air must be displaced by water or my results will be incorrect * I allowed 5 minutes for the mixture to equilibrate * Then I started the stop clock * While the experiment is taking place, I made sure that the water is kept at the desired temperature, and that all the apparatus was still in place * I stopped the stock clock after 5 minutes * I accurately measured the amount of air (carbon dioxide) that has displaced the water in the small syringe. I was careful not to measure the top of the meniscus, but the bottom. I made sure that an error of parallax is not created, by making sure that my eye was in line with the object. * I then recorded results and observations Safety Precautions When working with the higher temperatures such as 50 and 60 degrees Celsius, wear rubber gloves. This will prevent burns and pain caused by the hot water. Be careful not to drip water over any electrical appliances such as the kettle. Do not carry hot or boiling water around the classroom at any time: keep a beaker or kettle next to you if you need hot water at hand. Wear a lab-coat. Take care at all times when handling equipment. Any earlier work that helped my planning: We have studied the respiration of yeast during class, and most of this information can be found in our textbooks or else on the Internet (e.g. www.bbc.co.uk) or software programs (e.g. Microsoft Encarta) Obtaining Evidence The equipment that I will use will allow me to obtain precise results. There may be more accurate alternatives - such as using a digital thermometer. ...read more.

Conclusion

I do not think I have enough evidence to say the exact temperature at which enzymes denature. My results are not 100 % accurate because I know that the temp was not kept constant at all times, that the yeast suspension may have had some variance in glucose concentration (because other student may have dipped their syringes into the yeast suspension after dipping them into glucose solution). One way I could improve my method would be to redo the entire experiment again. This would minimize chance of error as well as making sure my results are correct. The more experiments I could repeat the better, although the only problem is the lack of time. Other ways to improve my experiment: I could make sure that my syringe was completely clean every time I dip it into either the glucose or yeast solution. Check that the rubber tube is completely secure on the syringe, allowing no air to escape. Check the apparatus before starting each experiment to make sure there were no mistakes in this area. Make sure I start my stop clock exactly as the experiment starts. It may be better to have an alarm on the stop clock so that it will ring at the exact time, thus it will be easier to take a reading at a correct time - as the alarm rings, instead of the slightly inaccurate method of looking at the stop clock until the correct time and then taking a reading. The temperature could be measured using a digital thermometer. This would give more precise readings. It would be easy to know when too add hot water, etc. and so will improve the reliability of the final results. Make sure no error of parallax occurs when measuring how much air was formed in the syringe. Do this by keeping the object and your eye in a straight line. Try to repeat the experiment as many times as possible, and making averages. Each time I repeat the experiment, my results will become more reliable. Luke Winter 11X Biology c/w Respiration of Yeast 2003 1/10 ...read more.

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