Prediction
I predict that the concentration of glucose (C6H12O6) will affect the rate of respiration (the amount of CO2 per time unit). I believe that the more glucose added (to a certain amount) will slow down the rate of respiration. If too much glucose is added, the active sites on the Yeast enzymes are de-natured. The less glucose present, the reaction would speed up. This can be explained by these two theories: The Kinetic Theory and the Lock and Key theory. The Collision theory states:
“The higher the temperature, the quicker the reaction. The heat increases the energy, and speeds up the collisions. If the temperature is too high, the enzymes de-nature.”
The Lock and Key theory is when the glucose and the enzymes successfully collide. If the temperature gets too high, the active site will de-nature. The active site loses its unique shape; therefore, the glucose will not fit into the enzyme to create an enzyme-substrate complex.
I will use five concentrations of glucose:
I will measure the CO2 produced after every minute for five minutes during three repeats of the same concentration.
The next three pages is a Preliminary Investigation, then the main Investigation Results long with the line graph.
Preliminary Investigation
I am going to measure the rate of CO2 produced by yeast when supplied with three different concentrations of glucose. I will measure the rate by determining how much CO2 is produced at a given time.
Materials and Method
Materials
10% Suspension of yeast
5%, 10% and 20% (w/v) Glucose solution
Stopwatch
50cm3 Burette
Clamp stand
Large bowl
250cm3 Conical flask
200cm3 Beaker
Rubber bung with delivery tube
Thermometer
Filter funnel
Measuring cylinder
Method
Results
See graph on the next page
Preliminary Conclusion
I can conclude from this that respiration is a simple method including the breakdown of sugar unless the concentration of Yeast in the experiment has been made higher or lower. I have measured the change in Yeast in the above table and it has proved my Prediction. I am satisfied with my results but I believe I could have improved by:
- Recording results twice for every concentration
- Increasing the variety of concentrations for the experiment
- Checking every piece of equipment that is clean before experiment
Results
0% Concentration
5% Concentration
10% Concentration
15% Concentration
20% Concentration
Conclusion
The above two sets of results and the two line graphs are very promising, when confirming my prediction. Both the results, interpreted into the line graphs show that if you have a low concentration, then respiration in yeast slows down immensely and is almost non-existent. However, if there is a too high concentration then, as I explained earlier, the active-sites on the yeast enzymes de-nature and the glucose is unable to connect with it, forming the enzyme-substrate complex.
The trend of results is pretty evident from my results table and my graphs. They show that as the concentration of glucose increases, the accumulative volume of Carbon Dioxide increases also. This can be proven in my graph.
There are certain 'fair test factors', which are out of my control, such as that condition of the materials before I use it, unknown substances in the yeast of glucose solution and the status of room temperature. These may not deviate my results but I would prefer to keep them under control.
Considering this investigation correctly proves my prediction, I can make another investigation, using another factor such as using varied temperature. I believe the results would be roughly the same, but if the temperature gets too high or low, then I believe the 'Lock and Key Theory' and the 'Kinetic Theory' will be proved correct and the reaction would not take place.
This is an example of a normal enzyme-substrate complex forming:
This, however, is what would happen if the enzyme would de-nature.
Evaluation
The quality of the results gained were not as close together as I had hoped by they all show one distinctive pattern: as the time increases, the amount of water/carbon dioxide increases/decreases. This alone can prove my hypothesis.
My graph – page 7 - is used to prove the results by plotting the average CO2 volume in every concentration against the minutes used in the experiment. The quality is clearly read and the graph is accurate.
If I was to repeat the experiment, I would make a number of changes: Increase the concentrations up to 30%; I would make more graphs with different information on them, such as accumulative volume, more graphs that include every result. With the results already gathered, I would do a fourth experiment to even further clear up the average number.
The results I have recorded are valid to the last number. They have been repeated three times to get a good average and each average seems to follow in the pattern of increasing each time. Each reading was similar, however sometimes they varied in increasing and decreases instead of a constant pattern. This is not a problem, however. It is to be expected because each column of result was a different experiment.
The suitability of the method was very good and clear and was easy to adhere to. There are only two seen improvements – by not being able to control the amount of agitation the yeast solution receives before the experiment may stop the validity of the experiment. The second improvement is that all the equipment should have been washed thoroughly beforehand so that no foreign germs may having effects while the experiment is taking place.
To continue with the experiment, I had to make sure I had enough reliable evidence to make a prediction, a reliable experiment and a conclusion. I achieved this by trying a Preliminary Investigation before starting the main one. My hypothesis was correct and results were reliable evidence to suggest a larger experiment would be successful. I learned some safety precautions and method advances after the Preliminary Investigation to ensure a safe and valid experiment.
Further work could have been tried to try to enhance the experiments legality. I could have used more experiments on the batch of Yeast to make sure that its contents were 100% pure. I could have used apparatus to agitate each sample of Yeast together so that they are identical to each other.
