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An investigation to find the lowest temperature that kills all the yeast cells in a suspension of bakers yeast.

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Introduction

An investigation to find the lowest temperature that kills all the yeast cells in a suspension of bakers yeast. Contents Page 1 - Hypothesis and introduction Page 2 - Introduction, risk assessment Page 3, 4 - Risk assessment, Pilot study (method, results, conclusion and evaluation) Page 5 - Variables, Equipment list Page 6 - Equipment list, Precision and accuracy, final method Page 7 - Final method Page 8 - Intended treatment of results, References Page 9 - Evaluation of references Hypothesis This investigation involves studying the fungi, yeast, to see how it responds to different temperatures. Based on the effect high temperatures will have on the enzymes of the yeast a sensible prediction would be that higher temperatures, above the optimum, around 50�C would kill yeast cells. Introduction Yeast is a unicellular, eukaryotic, fungus and as so generates energy from respiration as shown below in this simplified equation. Inside the yeast cell enzymes control this reaction. Enzymes are globular proteins which act as biological catalysts maintaining vital reactions such as respiration. Temperature is a major factor that affects the rate of an enzymes activity. As the temperature increases so does the kinetic energy that both the enzymes and substrates possess; which means there will be a greater number of enzyme - substrate collision and thus a greater rate of reaction. ...read more.

Middle

Evaluation This was strictly a preliminary experiment as there were many aspects which make it simply a guideline for a further experiment. Firstly there was only one test tube for each temperature meaning it was not an average reading which is far more accurate. The other flaw was that just saying whether or not the yeast was dead or alive seemed unsatisfactory. By means of a counting chamber, it would be possible to discover how much yeast survived in a particular area. However as a preliminary experiment it served its purpose as it gives an approximate suggestion to where yeast enzymes are denatured, which means a more suitable range of temperatures can be used. Variables - Dependent and Independent My independent variable is the single variable I will adjust in order to study the effect it has on the experiment is the temperature of the water bath the test tubes of yeast and glucose and submerged in. The dependent variable is the percentage of yeast alive at the end of the experiment, which is by my prediction directly proportional to the temperature. Constant Variables * Concentration of yeast - Changing how much yeast is present in 0.5cm�of solution each time would give a useless value for the percentage alive. ...read more.

Conclusion

12. Shake the test tubes and then use another pipette to remove a few drops of the solution and place it on three slides and cover with slips. 13. Carefully place the slides under an electric microscope, focus it and examine the slides. 14. Using a counting chamber of 1cm� measure how many yeast cells are alive in this area. 15. Take the mean for how many cells remain alive in this area. 16. Repeat stages 5 to 16 for 40�C, 45 �C, 50 �C, 55 �C and 60 �C. Intended treatment of results Once the experiment is completed I will process the results into a table. -A table to show the percentages of yeast cells alive at various temperatures- Temperature/�C % of yeast alive Average % of yeast alive Run 1 Run 2 Run 3 35 40 45 50 55 60 The first average where 100% of the yeast cells are killed gives the lowest temperature where all yeast dies. By studying the range and uncertainty it can give an approximation to how accurate the results are and account for any significant anomalies. This means that if a significant anomaly is detected it can be disregarded or re -run to account for the random error. References Resource Format Biology 1 (OCR) pages 42 -47 Book Collins advanced science - biology pages 90 - 94 Book http://en.wikipedia.org/wiki/Enzymes Website www.ubi.ca/cart/images/images/enzymes.JPG Website www.examstutor.com/biology/resources/studyroom/biochemistry_and_cells/enzymes/pictures/temperature/.gif Website http://en.wikipedia.org/wiki/Respiration_%28physiology%29 Website http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/Enzymes. ...read more.

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