An investigation into the effect of temperature on the rate of reaction of yeast.

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The pH of the solution would alter the rate of the reaction if it was changed therefore I must keep it constant, it will not change. It alters the rate of reaction because when it is acidic H+ ions interfere with the enzymes and their active site.

Prediction

I predict that as the temperature increases, the speed of the reaction will increase. When a particular temperature is reached I believe the rate of reaction will dramatically decrease. I believe this because most chemical reaction happens faster when the temperature is higher. At higher temperatures molecules mover around faster, which makes it easier for them to react together. Usually, a rise of 10OC will double the rate of reaction. This is true for enzymes up to about 40°C. However at 40°C the enzyme begins to be denatured, where the active site changes shape and so the substrate doesn’t connect with the enzyme (lock and key), so the reaction slows down. By around 60°C the enzyme is completely denatured. The graph below shows the trend I believe the results will follow:

 

I also predict that there will be no results after the temperature has exceeded 70°C or before 20°C. this is due to a previous experiment which was similar where there were no results at these temperatures with another enzyme called amylase. I think that there will be no results after 70°C because the active site of the enzyme in the yeast has changed shape and therefore it doesn’t connect with the substrate. And therefore didn’t react. Before 20°C I think that the collision theory comes into affect, as the enzymes do not have enough kinetic energy to collide with enough force to cause a reaction.

Information from preliminary work.

My preliminary work helped me fine-tune my plan of the experiment by illustrating several key faults in the experiment. The first thing I found out was what quantities of yeast and substrate (glucose solution) to use in the experiment. First I decided to use 1 gram of yeast then I had several different amounts of glucose solution. I found that less that 15ml meant that there wasn’t enough sugar for the yeast in the 6 minutes of timing. And I found that with more than 15ml then the froth from the reaction meant that some solution pasted up the tube. I also found that the yeast required a period of time in order to re-activate, I found that the best length of time was 5 minutes; I got a steady stream of bubbles after this length of time. From my preliminary work I also found that by doing more than one repeat I could get a more accurate result and at the same time I could eliminate anonymous results. I have also seen that there is not enough gas at temperatures below 20°C to measure with the syringes we have been provided. I have also seen that temperatures above 70°C do not change the amount of gas at all, there is none being produced. I have found that it the temperature of the water bath goes down and therefore the temperature of the solution is going down. I am going to have to add hot water from the water bath to keep the temperature the same through out the time; re-activation time and timing time.

I managed to make a table of the results from the preliminary work:

Range of conditions

I have chosen the range of 20°C to 70°C as I have seen from my preliminary work that temperatures either side of this band are of no use to the experiment.

List of variables and how they are going to be controlled

1. Independent. The only variable I am going to change is the temperature of the water, hopefully in, 10°C intervals. By changing the temperature of the water bath of which the boiling tube is placed in.

2. Dependant. I will measure the volume of gas that is produced by the reaction of the yeast and the glucose in a syringe. I will measure it in cm3 / 2 minute interval. The syringe is placed under water so that the CO2 pushes the water out of it and this gives us an accurate reading of CO2 produced by the reaction. To stop any gas escaping a Hoffman clamp is placed on the end of a rubber tube attached to the syringe.

3. Fixed. The variables I will have to keep the same are the concentration of substrate ([S]) and the concentration of enzymes ([E]). This is so that there is not an unfair test. If there was a higher concentration of enzymes there would be more likeliness of a collision and so there would be a larger amount of gas produced; thus the mass of yeast will have to remain constant to keep it a fair test. Similarly due to the collision theory there will be more collisions and so the reaction will go faster, if there is more glucose in the solution. I will also have to keep the room temperature around the same in order to make it a fair test. The temperature of the water bath must also stay the same or else the temperature of the solution will decrease and so making it an unfair test.

Number of repeats.

I will repeat my experiment 3 times at each of my 10°C intervals (20°C, 30°C, 40°C, 50°C, 60°C and 70°C) this is so that I avoid any anomalous results and it increases the accuracy of my experiment. The repeats I will do will be at 2-minute intervals after a re-activation period, 1 at 2 minutes, 4 minutes and 6 minutes. It would be even more accurate if I could do more than 3 times but there isn’t enough time to do this.

List of apparatus

Thermometer

Water

Yeast

Glucose solution

Boiling tube

Beaker

Syringe

Delivery tube

Hoffman clip

Stirring rod

Basin

Method

• I measured out 1 gram of yeast and placed it in a boiling tube.
• I got a large beaker and filled it with water to the temperature I wanted the glucose solution to be.
• I collected the glucose solution in a syringe (15ml); it had already been heated in a water bath before hand.
• I filled another syringe with water in a basin of water and attached a Hoffman clip to a rubber tube coming from the syringe, to avoid any gas from leaving.
• I added the glucose to the yeast and left it to re-active, till a steady stream of bubbles came out of the delivery tube, attached to the boiling tube.
• Then I put the delivery tube so that the bubbles of CO2 went into the syringe of water, and so pushing the water out and measuring the amount of CO2 produce.
• I timed 2 minute and recorded the amount of CO2 produced. I did this 3 times.
• I then did it at the other temperatures and repeated the method as above.
• I recorded my results in a table of results.

Safety

Before starting there are a few safety aspects, which I have to be careful of. Firstly I need to be careful of the water, as some of it is very hot.

Obtaining

A table to show the results from an experiment into the effect of temperature on the rate of reaction of yeast.

All anomalous results were repeated and not used in working out the average amount of carbon dioxide given off per 2-minute interval. The anomalous results are highlighted in the table in red. The figures in the average column are to 1 significant figure.

Analysis