Yeast Respiration Lab

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“Investigate the factors affecting the rate of yeast respiration” Lab Report

Introduction

The aim of this experiment was to investigate the effect of different amounts of a substrate on the respiration rate of yeast and to compare this to the effect of different amounts of glucose on the rate of yeast respiration. The substrate which I chose to further investigate was fructose. Fructose is a fruit sugar which is one of the three, along with glucose and galactose, dietary monosaccharides that are directly absorbed into the bloodstream during digestion.

Apparatus

2% yeast solution
Large beaker
Small beaker
Conical flask
Thermometer (˙C)
Glass rod
pH meter & data logger
Hot water
Sensitive digital scale (g)
Fructose (1.0g, 1.5g, 2.0g, 2.5g)
Glucose (1.0g, 1.5g, 2.0g, 2.5g)
Measuring cylinder (cm3)

Variables

Independent: Concentration of glucose (1.0g, 1.5g, 2.0g, 2.5g) , concentration of fructose (1.0g, 1.5g, 2.0g, 2.5g) Dependent: Amount of carbon dioxide produced, i.e. rate of yeast respiration Controlled: 2% yeast solution (20cm3), initial temperature of yeast solution (35-40˙C), amount of time that the reaction is measured (180 seconds)

Method

All apparatus was collected and safety precautions (hair tied back, safety goggles and lab coat) applied 20cm3 of 2% yeast solution was measured out, using the measuring cylinder, and poured into the conical flask 1.0 ±0.5g of glucose was weighed out on the sensitive digital scale Hot water was then poured into a large beaker into which the conical flask, containing the 2% yeast solution, was held in place in, with a thermometer inside The conical flask was held like this until the 2% yeast solution reached an initial temperature between 35-40˙C (specific temperature was noted down) When this temperature was reached, the thermometer was taken out of the conical flask and the conical flask out of the hot water 1.0 ±0.5g of glucose was quickly added to the 2% yeast solution, inside the conical flask, and mixed only a little, enough to dissolve the glucose Meanwhile, the pH measurer was quickly placed into the conical flask and the data logger was started when the active ingredient, i.e. glucose, was added This setup was left until the data logger reached a time of 180 seconds, at which point it was stopped and the pH measurer was taken out of the solution and placed into a beaker with clean water to prevent build up The final temperature of the 2% yeast solution was measured and noted down to ensure that the temperature loss, in comparison to the other trials, would be the same and therefore not affect the results Steps 1-9 were repeated 2 more times to give a total of 3 Trials which ensured fair testing Steps 1-10 were repeated using different amounts of glucose (1.5g, 2.0g, 2.5g) Steps 1-11 were repeated except that instead of glucose, fructose was used The pH meter measured the change in pH, which was recorded in the data logger and printed off as tables An average of each solution's 3 trials was taken

The data was then converted into graphs from which the gradient was calculated to give the rate of yeast respiration

Data
1.0 ±0.5g + 2% yeast solution |
Glucose | Fructose |
Time (s) | pH | Time (s) | pH |
0 | 6.4 | 0 | 6.4 |
30 | 6.2 | 30 | 6.3 |
60 | 6.1 | 60 | 6.2 |
90 | 6.1 | 90 | 6.1 |
120 | 6.0 | 120 | 6.0 |
150 | 6.0 | 150 | 5.9 |
180 | 6.0 | 180 | 5.8 |

1.5 ±0.5g + 2% yeast solution |
Glucose | Fructose |
Time (s) | pH | Time (s) | pH |
0 | 6.4 | 0 | 6.3 |
30 | 6.3 | 30 | 6.1 |
60 | 6.3 | 60 | 6.0 |
90 | 6.1 | 90 | 5.9 |
120 | 6.0 | 120 | 5.8 |
150 |...
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