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The effect of temperature on the survival of yeast cells

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Introduction

PLANNING EXERCISE The effect of temperature on the survival of yeast cells. The aim of my investigation is to find the lowest temperature that kills all the yeast cells in a suspension of either dried or fresh baker's yeast. I predict, as yeast cells contain enzymes and enzymes usually only functions best at about body temperature, which is 37oC. As the temperature increases from 40oC, the function of enzymes starts to slow as they begin to denature till it reaches about 50oC. Any temperature above this will denature the enzymes and therefore kill them. In this case, I also predict that the lowest temperature range that would kill all the yeast cells is roughly between 10oC and 60oC. BACKGROUND INFORMATION Yeast is a member of the fungus family and is a single-celled organism. Baker's yeast as well as brewer's yeast is similar in that they belong to the same species called the saccharomyces cerevisiae. Yeast cells are sensitive to changes in temperature and therefore it affects its structure and activity. This is because its metabolism is carried out in the presence of enzymes which are active only in an optimum range of temperature. Higher ferment temperatures increase yeast activity and vice-versa. The optimum temperature range for yeast fermentation is between 32oC and 38oC. A high temperature at about 50oC destroys these enzymes and therefore kills the yeast cells. Other factors affecting yeast activity are pH and concentration of sugar. ...read more.

Middle

* Dropping pipettes * Beakers (250ml) * Microscope * Slides and Cover slip would suggest Haemocytometer slides RISK ASSESSMENT Hazardous substances What is the hazard Risks Precaution Emergency Action Ethanol Highly Flammable High Naked flame should not be present when ethanol is in use. If flame ignites, put out by using fire blanket or fire extinguisher. Methylene Blue Irritant/harmful Irritant to skin, eyes and lungs. Medium Wear gloves, avoid naked flames if using flammable solvents. Use low concentrations. Flood eye with tap water. Baker's Yeast Irritant Low risk, could cause allergic reactions Use low concentrations, wear gloves to protect skin Flood eye with water if in eye Carbon dioxide Danger Medium Can cause asphyxiation at high concentration Use low concentration of yeast to limit the amount of carbon dioxide produced. If large quantities breathed in, remove to fresh air. Glucose /Sucrose Low hazard Low Do not consume any sugars or any food or drink in laboratories as it may be contaminated. Wipe up solution spills with a cloth, brush of contaminated clothing and wash off skin Water bath Burns Medium Keep in a safe and secure place. If skin burnt, place under cold water. Test tubes They can break Low Take care when Handling. Prepare cleaning up material Dispose of sharp glass immediately if broken. METHOD I will test out 5 temperatures; these will range from 10oC to 50oC with 10 degree intervals. ...read more.

Conclusion

Based on my preliminary investigation I found that it was difficult to have the same amount of methylene blue because it was hard to control the size of the drops therefore it makes my experiment unfair. I will therefore suggest using a dropping pipette which is more accurate. I believe it would make my results more accurate if the temperature in the water bath was measured as it can either rise or fall due to the yeasts activity. I carried out my preliminary without using a water bath to keep the temperature constant but instead a Bunsen burner. I think using this, causes a lot of errors and it's not very accurate because the temperature might constantly rise above the temperature that you are testing or below and therefore it's not reliable. I heated the test tubes for ten minutes. After that I took a sample of my solution and placed it on a slide. And then put a drop of methylene blue around the edge of the slide. I then viewed this slide on a light microscope and observed the colour of the yeasts. I think viewing it under a microscope to look for a colour change is also not very accurate because it will be hard to view all the yeasts in a microscope and count how many are colourless or otherwise blue. I will therefore be more accurate to use a haemocytometer, a specialised microscope slide with a grid which is used to count cells. ...read more.

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