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Biology Coursework Essay

Aim : To find out how temperature will affect the amount of carbon dioxide given off from yeast.Prediction : I predict that the cooler the water we use is, the less bubbles will be produced, if any at all. I think this because the warmer the water the molecules move faster/collide/react and more carbon dioxide will be given off from the yeast due to the enzymes respiring (fermentation). However I know that the enzymes that produce the carbon dioxide via fermentation will certainly denature after exposure to temperatures above that of 40oC. So I believe that anywhere between 20-40oC will produce a good amount of bubbles, less than 20oC will stop the enzymes from being able to produce carbon dioxide because they will simply stop.And above 40oC will more than likely denature the enzymes, resulting in no carbon dioxide bubbles being produced. Previously I conducted a trial experiment to this one. It involved pouring yeast into a test tube and attached a balloon to the top. After I had done this. I found that yeast defiantly did respire as the balloon filled up over time. However there was no accurate way of measuring the amount of carbon dioxide given off by the yeast so I was unable to properly conclude that experiment.Theory :The enzymes react like a lock and key, only one lock fits the key. When the two join then you get the chemical reaction. When too much heat gets applied then the lock gets changed and so the key doesn’t fit the lock so there is no reaction.Safety : To perform this experiment I need to keep myself safe. To do so I will be wearing goggles at all times and when I am putting the bung on the test tube. I will not use my palm to push it down, as this can lead to the glass shattering as my hand goes past it.Apparatus List :For the experiment, I will need : BungBoiling TubeClamp StandMeasuring CylinderSmaller Test TubeWaterThird Test TubeFair Test : To make this a fair test, I will need to keep the same amount of water used in every experiment. The yeast will also be kept the same. I will use the same equipment every time I do an experiment in case yeast is left over in a measuring cylinder.Diagram :Method :1. Set up all of the equipment as shown in the diagram2. Measure 25cm3 of water, fill the boiling tube up3. Measure 20cm3 of yeast, pour it into the smaller test tube4. Heat the yeast to 20oC5. Count the number of bubbles formed in the test tube linked to the yeast one.6. Repeat steps 2-5 using different temperatures (40oC, 60oC, 80oC and 100oC)7. Collect results for all of them.8. Now conclude the experiment, look at the results found, make a sensible conclusion from them. Ie. The higher the temperature, the more bubbles formed, going over 40oC will stop any carbon dioxide bubbles from appearing due to denaturing the enzymes.Results :TemperatureNo. Of Bubbles Found20oC040oC060oC080oC0100oC0Conclusion :I am unable to conclude this experiment because I haven’t gained proper results which have told me enough about how the temperature affects the rate at which fermentation occurs in yeast (gives off carbon dioxide.)Evaluation :In my experiment there were many odd results. In fact all of my results were strange. They all gave me 0 bubbles produced from the yeast. I think this is because we heated the yeast up for too long before we put the bung tube to the yeast tube, in that time most of the carbon dioxide would’ve escaped because we were heating it up. To avoid this problem I should have heated the water up before adding the dry yeast and sugar. We should have also mixed the yeast every time we took a sample. Maybe the main yeast cells had fallen to the bottom. If we shook the bottle the concentration would be equalled out instead of being at the bottom. Also temperatures above 50oC must have denatured the enzymes therefore we wouldn’t have gained any bubbles from the yeast. To gain perfect results I could’ve averaged my results but unfortunately I got 0 bubbles from all 5 temperatures.I could have changed the water used in the boiling tube to a liquid which is less affected by temperature. I could also use an electric thermometer which would help me greatly as a manual thermometer isn’t as accurate as an electric one would be. Finally I could have conducted another experiment to check if concentration of yeast affects the rate of which it respires. I could have kept the temperature at an optimal rate (40oC or so) and tried different concentrations of yeast

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