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Introduction

What effect does substrate have on respiration in yeast? AIM The aim of this investigation is to find out how the rate of respiration in yeast is affected when different respiratory substrates are used. Five different respiratory substrates will be used and the amount of carbon dioxide produced will be measured for each substrate. The five substrates that will be used are glucose, fructose, maltose, sucrose and lactose. HYPOTHESIS Null hypothesis, H0: There is no significant difference between the amounts of carbon dioxide produced by yeast during respiration, regardless of the respiratory substrate used. Alternate hypothesis, H1: There is a significant difference between the amounts of carbon dioxide produced by yeast during respiration, depending on the respiratory substrate used. PREDICTION Natural habitat of yeast is the skin of fruit, which usually contains fructose and glucose and in some cases sucrose. Yeast is also found on malt so it is familiar with maltose as well. Therefore it will be able to secrete the enzymes needed to break down glucose, fructose, sucrose and maltose. However, lactose is present in milk and other dairy products, where yeast does not live. As a result, it is likely that yeast would not have the enzyme, lactase, needed to break down lactose. The table below shows each substrate, the enzyme needed to hydrolyse this substrate and what the substrate is broken down into. Substrate Enzyme Broken down into: Glucose Zymase Ethanol and Carbon dioxide Fructose Zymase Ethanol and Carbon dioxide Maltose Maltase Glucose Sucrose Yeast invertase Glucose and fructose Lactose Need Lactase Glucose and galactose Although glucose ...read more.

Middle

35g of dry yeast To make yeast suspension. 3 x 1g Glucose A respiratory substrate; monosaccharide 3 x 1g Fructose A respiratory substrate; monosaccharide 3 x 1g Maltose A respiratory substrate; disaccharide 3 x 1g Sucrose A respiratory substrate; disaccharide 3 x 1g Lactose A respiratory substrate; disaccharide METHOD Steps Reasons for doing it 1. Prepare the yeast solution in a 400ml beaker by mixing 35g of dry yeast with 350ml of warm water. Make sure to place 50ml of buffer solution in this beaker before the yeast suspension is made. This would ensure the total volume of the solution is 400ml. Buffer solution will be needed to resist any change in pH during respiration of yeast. 400ml of yeast suspension should be enough for 15 repeats and will allow for any errors. 2. Place this beaker in a water bath of temperature 35oC for about 60 minutes. This will ensure that any sugars present in the yeast are used up before the experiment is conducted. The temperature used is 35oC, as it is the optimum temperature at which the yeast respires. 3. During this time set up the other equipments. Fill a 100ml graduated cylinder with coloured tap water. Colour tap water is used as this will make it easier to read off the graduated cylinder. 4. Place the graduated cylinder upside down in a large beaker filled with same coloured tap water. Make sure the graduated cylinder is fully filled with water. ...read more.

Conclusion

RESULTS The results will be set up in the table shown below amount of CO2 produced (cm3) Substrate Glucose Fructose Sucrose Maltose Lactose 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 Time (mins) 5 10 15 20 25 30 35 40 GRAPH Key Glucose Fructose Sucrose Maltose Lactose After conducting this experiment I will carry out the t-test on the results obtained. T-test is a statistical test used to analyse the difference between two sets of data but a large sample is needed in order for the t-test to be used. By carrying the t-test I will be able to prove that my null hypothesis is not true and that there is a significant difference between the amounts of carbon dioxide produced, depending on the substrates used. The formula used to work out the t-value is: x1 - Mean of first set of data x2 - Mean of second set of data s1 - standard deviation of first set of data s2 - standard deviation of second set of data n1 - number of values in the first set of data n2 - number of values in the second set of data t - t-test value The t-test value worked out will be compared with the critical value on the t-value table. I will be testing the hypothesis at 5% level. This means that I will be 95% certain that there is a significant difference between two sets of data if the null hypothesis is rejected. Null hypothesis will only be rejected if the calculated t-value is greater than or equal the critical value. ?? ?? ?? ?? Elakkiya Sunthararajan ...read more.

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