AT1 practical assessment – yeast respiration

25ml water

1g yeast

2g glucose

This gave us 0.3ml of carbon dioxide over 4 minutes.

I found the third experiment very hard to measure and carry out accurately, and it gave a poor result. So I decided to try and investigate the temperature, as it was easier and had given a much better result.

To help me decide on my measurements, I researched how other students had done the experiment. I found two examples on the Internet, one of the temperature experiment and one of the concentration experiment. One experiment measured the carbon dioxide produced every minute, and the other timed how long it took to produce 2ml of carbon dioxide.

Using this, and the experiment I had tried out, I decided to measure the amount of carbon dioxide produced over 3 minutes. This would be more appropriate considering the rate of respiration I was expecting.

APPARATUS ⇨ 

Stand and clamp

Conical flask

Bung and delivery tube

Ice cream tub and measuring cylinder filled with water to measure carbon dioxide.

Water

Glucose

Yeast

Stopwatch

Beaker to be used as water bath

Kettle and ice to vary the temperature of the water bath

Safety goggles

METHOD ⇨ 

Firstly, I set up all my apparatus as above, and then put 25ml of water, 1g of yeast, and 1.5g of glucose together in the conical flask to begin the respiration.

I then submerged he flask in the water bath at the lowest temperature of 10C. I attached the delivery tube to the bung in the flask, and then placed it at the bottom of the measuring cylinder, in the ice cream tub full of water. This was to measure the carbon dioxide, by the displacement of the water, after 3 minutes. Once this had been recorded, I repeated the experiment three times to make it fair and ensure there were no inaccurate results.

Then I increased the temperature in the water bath to 20C, and did the experiment again. I continued to do this with the measurements going up in 10s, so I had 6 results ranging from 10  C to 60  C.

I made the experiment safer by using a kettle rather than a bunsen to heat water, and by wearing safety goggles.

PREDICTION ⇨

I predict that increasing the temperature will increase the rate of reaction. The reaction will produce approximately 3ml of extra carbon dioxide for every 10  C the temperature is increased by.

I am basing this prediction on two things, the collision theory, and my preliminary work.

The collision theory, as mentioned earlier, says that increasing the temperature will speed up the respiration, because the glucose particles will have more energy, and they will collide with the active site of the yeast particles with greater frequency and force.

I think that the amount of carbon dioxide will increase in 3ml amounts because of the results of my preliminary work. The ‘control’ experiment was carried out at room temperature (approx. 22  C) and the temperature variable experiment was carried out at 35  C. The difference in temperature between the two is 13  C, and the difference in carbon dioxide produced was 3.8ml. This gave me a rough basis for this prediction.

RESULTS ⇨

CONCLUSION ⇨ 

My results show that increasing the temperature increases the rate of respiration. On average, the amount of carbon dioxide produced for every 10  C rise is 3.3ml, so my prediction was very accurate. However, the rise of 3.3 was not consistent, and as the graph shows, the biggest rise was between 30 and 40  C. There was also less change at the end of the experiment, as the yeast begin to denature.

This has proved the collision theory, as the respiration increased with the temperature variable.

EVALUATION ⇨ 

My experiment was quite accurate. However, there may have been small inaccuracies in:

• The temperature of the water bath. It may have not been exactly right, the thermometer may have been read inaccurately, or the temperature may not have remained constant throughout the 3 minutes the reading was taken over.
• The time the carbon dioxide was measured over. The stopwatch was probably not stopped at exactly the same point every time, and so there would have been a small amount of error, and the times been slightly different for each measurement. However, this would probably only have been a small error, and not noticeably affected the results.
• The amounts of glucose with the yeast, because we were not using a fresh glucose, water and yeast mixture for each experiment. As the respiration took place, more glucose was being used up, and so the concentration was decreasing.

If I were to do this experiment again, I would change the following things:

• Use a more accurate way to measure the temperature of the water bath, and keep it constant.
• Use a more accurate time measurement.
• Use a fresh yeast, glucose and water mixture for each experiment. However, this was not possible because we did not have enough mixture for the whole group to do this. The only problem with this would have been making sure we kept the whole batch of yeast stirred up, so the yeast did not settle.

These measures would ensure I got more accurate results.

To extend the investigation, I could investigate how the concentration affects the rate of respiration as well. This would enable me to compare the two variables and decide which has the greatest effect.

I had an anomalous (wrong or unusual) result. I pointed this out on my graph, by circling it in blue.       I think this was caused by some of the inaccuracies mentioned above, because it is not a largely wrong result, just outside of the curve.

My investigation has clearly showed that temperature affects the rate of respiration.