Investigation Of Yeast Respiration

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I will be investigating the respiration of yeast when adding more glucose.

Variables Temperature

Amount of sugar solution.




Amount of yeast.

Concentration of sugar solution.

Amount of shaking and acclimatization

We are going to measure the amount of Co given off from he yeast respiring as we add more sugar solution every mins, recording the amount of Co every minute.

Temperature will affect the rate of yeast respiration. I shall keep the temperature of he mixture and water bath under control by using a thermometer and checking it constantly. I shall also keep swirling the thermometer to keep the heat distributed. Also, as it will take longer for the temperature inside the test tube the same as the water bath, I shall leave the apparatus for two minutes, keeping the temperature constant.

The amount of yeast used in the experiment will be kept the same.

The concentration of the sugar solution will also be kept the same and we will use only one batch else if two different batches are used this will upset the results.

Acclimatization and shaking will help to activate the yeast and prepare the solution for timing. If it is improperly mixed, acclimatized to temperature or activated, the results would not be fair and inaccurate. I will shake the flask thoroughly each time I add a further 5ml of sugar solution until I can see bubbles being created. I shall also leave the flask in the water bath at the required heat for two minutes before the experiment is carried out.

Prediction I predict that the yeast’s respiratory rate of reaction should increase in speed as the % of glucose increases. However this may at some point peak and therefore cease to increase in speed.

My reason for the above prediction is that yeast is a unicellular fungus, which feeds saprophytically and can respire both aerobically and anaerobically. In the experiment the yeast will be respiring anaerobically and breaking down the glucose stored in it as a waste product of this process it will also form CO and alcohol in the form of ethanol. This respiration process is called fermentation. The yeast breaks down the glucose using a series of enzymes.

I deduce from this that the more glucose that is present in the yeast the more will be broken down and therefore more CO and ethanol will be produced as waste products at a faster rate. There are two main types of respiration, aerobic and anaerobic. Aerobic respiration releases more energy than anaerobic respiration. In aerobic respiration glucose is combined with oxygen to be converted into carbon dioxide and water releasing energy.

Method My method is as follows

1. I will place the flask of yeast into a tray of hot water (which will be kept at the same temp throughout the experiment)

. I will take a test tube of water and place the delivery tube into the water (as show in the diagram)

. I will then add (using the syringe) 5ml of sugar solution and replace the bung and start the stop watch.

4. I will count the amount of bubbles that come out of the receiving tube into the test tube. And record the about each minute.

5. After mins I will add another 5mls of sugar solution and repeat the process.

Diagram of Apparatus

To make this a fair test

I will be taking recordings of each amount of sugar water before adding another 5mls.

I will be making sure I get consistent results, otherwise I will repeat the experiment until consistent results are given.

Certain safety precautions must be taken When dealing with yeast and alcohol I must make sure not to inhale or consume in any way anything during the experiment as a lot of it may be harmful in someway. Also if any glass is broken for any reason it must be cleared up properly and safely.

Results I have ensured that my results are accurate by controlling all the variables stated in my Planning. I also took care when using the equipment so as to retain continuity throughout the experiment. For this, I checked everything was set up correctly at each reading and prepared my solution in the same way. To make sure that the results were as reliable as I could make them, I calculated the mean of three results

Minutes 1 Average

5ml 10ml 15ml 1ml 1ml

10ml 54ml 54ml 5ml 56ml

15ml 68ml 66ml 7ml 6ml

0ml 8ml 8ml 7ml 8ml

5ml 11ml 10ml 16ml 1ml

I can see from the results and graph on the next page, that the trend was that the longer we left the yeast, the higher the volume of CO produced. Up to the point where the enzymes denatured. So the amount of Co being produced decreases as the enzymes denature until all the reaction has taken place and no Co is being given off.

Background Information I found some secondary information on the internet and put it together with some of my background knowledge to form the following information

Respiration is the release of energy from glucose or other organic substances. Energy is required for growth, repair, movement and other metabolic activities. The energy released from glucose in respiration is used to produce a chemical called adenosine triphosphate (ATP). ATP is where the energy released during respiration is stored for future use.

FERMENTATION is the breakdown of sugars by bacteria and yeast using a method of respiration without oxygen (anaerobic respiration). It involves a culture of yeast and a solution of sugar, producing ethanol and carbon dioxide with the aid of the enzymes.

All the ENZYMES are protein chains of amino acids. They exist in the form of a structure with hydrogen bonds holding the pitches together. On the amino acid molecules, there is R a group. They react with each other to form peptide bonds, transforming the chain into a -dimensional structure. Along the chain there are active sites where interaction between the enzyme and the substrate happens. These sites are sensitive to heat, like the hydrogen bonds that hold the D molecule together. When heat is applied to the enzyme, energy is given into the molecule. The active sites deform and the hydrogen bonds break, denaturing this enzyme. It would not be able to function as usual, and this is not reversible. This is called DENATURATION. The D structure would breakdown and the active sites would change in shape; they would not be able to accommodate the substrate any more. The analogy of this is to compare a key to a keyhole. If the keyhole has changed, the same key would not fit in any more, and the lock would not be unlocked. The same thing happens here, and fermentation could not continue after this has occurred. Also when the temperature is too low, the enzymes would not work because there is not enough energy for activities to happen.

Yeast has to make energy, stored as ATP to carry out all cellular functions. To do this they can respire both aerobically when there is plenty of oxygen, but where oxygen is short, they respire anaerobically; by this, they are called partial anaerobes. This produces less energy, but keeps the yeast alive. Pyruvic acid has to be broken down in respiration when formed by breaking down of glucose molecules, this can’t be done in the same way as it is aerobically when respiring anaerobically which is how the carbon dioxide and ethanol is formed through the zymase. Here is the equation for anaerobic respiration

glucose ----------------- ethanol + carbon dioxide +energy

C6H1O6 CH5OH CO 10 Kj/mole

Analysis The Graph is a curve, all of the results fit almost perfectly into the curve. The graph shows that by changing the amount of sugar in the solution the more carbon dioxide is produced. . I also found that the rate of respiration dropped of completely after a certain point, highlighting the denaturisation of the yeast’s enzymes.

Conclusion I have found that as I increased the temperature of the yeast solution, the rate of respiration of the yeast increased to a certain point where, as the temperature rose to a certain level, (in my case about 68ºC) the rate of respiration eventually cut off.

My hypothesis and prediction can be backed up with the findings; from looking at my results and graphs you can see the rise and fall of respiration. They are explained due to the theories of enzyme-substrate with lock and key and kinetics. Where these meet is when kinetic theory states that an increase in temperature means more particle collisions between reactants and so a faster rate of reaction, and in enzyme-substrate where the enzyme is sensitive to heat, and about a certain temperature, the active site will begin denaturing, so slowing and eventually stopping the reaction.

Evaluation of Experiment

The experiment went quite well as I was able to obtain accurate sets of recordings. I think that the method used was good but could be improved by a better way of keeping the yeast at the same temperature and the same concentration of the solution.

If I were to further investigate this experiment and my results, I would probably want to calculate the point where the enzymes begin to denature for respiration in yeast.



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