An Investigation to find out how Temperature Affects Respiration in Yeast.

The investigation is intended to demonstrate the way that respiration in yeast is affected by temperature. I have read up about respiration in yeast in Letts GCSE Study Guide, B S Becket’s Biology A modern introduction and Illustrated Biology, and Tortora Funke Case’s Microbiology An Introduction. This is my summary:

Respiration is the overall process of breathing, gas exchange in the lungs, and the breaking down of chemicals to provide energy in living things. Most organisms require a constant supply of oxygen to respire. During cellular respiration, the oxygen is combined with glucose that has been converted from food. Energy is released, together with the waste products of carbon dioxide and water. This method of respiration that uses oxygen is called aerobic respiration. The other method of respiration, when no oxygen is needed, is called anaerobic respiration. One such reaction is fermentation. During this reaction, glucose is broken down into ethanol and carbon dioxide.

Aerobic Respiration.

Anaerobic Respiration.

Yeast can respire using either method of respiration, though if in aerobic conditions yeast does not usually respire anaerobically. This is purely because during anaerobic respiration most of the potential energy in the glucose remains “locked up” in the ethanol.

Plan

The only gas released during both types of respiration is carbon dioxide. I will measure the volume of gas produced every minute for 10 minutes, when a flask containing a yeast suspension is placed in water baths of various temperatures. New yeast will be used each time I repeat the procedure at different a temperature in case the yeast looses efficiency or dies after each use.

The range of equipment in the school labs is limited, so this is what I will be using:

Before the stopwatch starts, the sealed flask will be placed in the pre-heated water bath before the yeast. This is to allow expansion of the air inside the flask. Once the air has fully expanded, the yeast will be inserted and the stopwatch started.

To discover accurately the effect of temperature on the reparation of yeast i.e. maintain a fair experiment, I shall be keeping the following variables at a constant:

Volume of water present in yeast suspension
Mass ...

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The range of equipment in the school labs is limited, so this is what I will be using:

To discover accurately the effect of temperature on the reparation of yeast i.e. maintain a fair experiment, I shall be keeping the following variables at a constant:

Volume of water present in yeast suspension
Mass of glucose present in yeast suspension
Mass of yeast present in yeast suspension
Volume of air present in the armed conical flask
Size of armed conical flask
Temperature of water bath (during each separate set of readings)

For each set of readings, I will have to change the following variables:

Temperature of water bath

Prediction

I predict that the yeast will respire faster as the temperature rises, until around 40°C. As the temperature rises above 40°C, the rate of respiration will decrease. This is because the enzyme Zymaze is used in yeast. Enzymes are biological catalysts. Upon collision with the desired reactants, the desired reactants fit into an active site and the probability of a reaction is increased. This speeds up the reaction without having to increase the temperature to an intolerable degree. As the temperature increases the probability of a collision between the Zymaze and reactants increases. Enzymes are proteins and their structure is damaged as the temperature rises above 40°C. This damage to the protein structure is called denaturation. If the enzyme is denatured, the desired reactants no longer fit into the active site properly. It becomes less and less affective as a catalyst, and the reaction gets slower and eventually stops. Also eventually, extreme temperatures will kill the yeast, stopping any respiration.

Until all the oxygen in the flask has been used, the yeast will respire aerobically. Once all the oxygen has been used, the yeast will then respire anaerobically. This means that carbon dioxide will be produced quicker while there is oxygen remaining in the flask.

I predict that a graph showing how temperature affects respiration in yeast would be similar to the first graph opposite (page3). As the temperature rises, the rate of carbon dioxide production increases until at 40°C when it decreases.

I predict that a graph showing how yeast respires at around 30-40°C would look similar to the second graph opposite. While the yeast is respiring aerobically, carbon dioxide is produced faster than when the oxygen has ran out and the yeast is forced to respire anaerobically.

Trial Experiment.

My trial experiment revealed one main problem. When the water bath is at temperatures above or below room temperature, the air contained in the armed conical flask and the yeast suspension either expands or compresses, this either causes bubbles of air to escape into the measuring cylinder, or water to be sucked up the delivery tube. I shall take this into account during my experiment and dedicate the first 3 minutes to letting the apparatus reach the correct temperature. In addition, I found that I do not need to take readings for a duration of 15 minutes, but that 10 minutes is adequate.

Results

Analysis of my results.

Contrary to my prediction, the average volume of gas produced per minute increased as the temperature increased, until approximately 60°C, after which I expect it to decrease. This suggests that at 50°C and 60°C, when the enzymes in the yeast are denatured, the amount of collisions between them and the reactants is increased so much that even though a few are not successful, enough are successful to make the speed of the reaction as a whole higher than at lower temperatures when all collisions are successful.

Also contrary to my prediction, the amount of gas produced did not decrease, since all of the oxygen was used up in the three minutes taken to let the apparatus reach the correct temperature.

Evaluation

My data contains at least one anomalous result. When the yeast was heated up to 50°C, in the sixth minute, 6ml of gas was recorded to escape into the measuring cylinder. This is twice as much as any minute before or after. There are a number of factors that may have caused such inaccuracies:

Because I took different sets of readings on different days, different equipment was used. This means there may have been slight variations in the sizes of both pieces of equipment on the different days.
The scale on the measuring cylinder is not extremely accurate. Therefore the readings recorded may not have been an accurate measure of the gas.
Human errors may have been made when reading off the scale on the measuring cylinder.
The seal between the armed conical flask and the delivery tube may have been broken.
The delivery tube may not have been airtight.
The rubber cork may not have totally sealed the flask.

The equipment I used was not to the level of accuracy need to collect reliable data. Ideally I would liked have used this equipment:

However, even if I had used this equipment, the following factors may still have caused inaccuracies in my results:

The yeast may have been defective.
The yeast suspension I used may not have contained the ideal concentration of water and sugar due to human error during preparation.
The yeast suspension, armed conical flask, and air contained within the armed conical flask may have been contaminated with substances that could have affected the yeast’s ability to respire.
The yeast suspension, armed conical flask, and air contained within the armed conical flask may have been contaminated with organisms that also will produce a gas during respiration.
Due to human error, the volume of yeast suspension used during each set of readings may have fluctuated.
The temperature of the electronic water bath will have fluctuated, since it uses a thermostat.
The clamp stand would cause the temperature of the armed conical flask to be imprecise.
Human error may have caused the stopwatch to be started too early or late.