- Glucose concentration
- Time
- pH
- Heavy metals such as Zinc
- Stirring
- Volume of yeast + Concentration
- Volume of glucose
Some of these factors will be controlled while others will be changed, or measured. Underneath you will see a table of what will be done.
How will each affect the experiment? In the next few lines I will explain each.
pH – The pH will have to stay close to neutral (7) to help this the glassware will be clean to stop any strong alkali’s or acid’s from affecting the experiment and ruining it. The pH if to high or low can cause the enzymes to denature by breaking the bonds that hold its structure.
Temperature – When the temperature is high (40°c) the enzymes can perform respiration quickly but if they get to hot then they start to denature. The temperature will also affect kinetic theory because as the particles get hotter the number of reactions increases so more CO2 is produced, but if the temperature increases too much then the enzymes start to denature.
Glucose – I will use 5 different glucose concentrations, and repeat each concentration experiment 3 times. This will give me a suitable range of concentrations, and the repeats will make me results more reliable. I will calculate an average of CO2 produced from each of the 3 repeats.
Degree of stirring – The degree of stirring or agitation of the flask will have to remain constant through the entire experiment, if this not done right it will result in inaccurate results, this is because the degree of agitation will help in the collisions between the enzymes and the glucose. If this is done wrong it will result in uncanny results.
Prediction:
I predict that as we use a less glucose/water concentration (%W/V) there will be less CO2 produced in 3 minutes, this is because there will be more water and less glucose. Due to there being a less glucose it will mean that there will be higher yeast to glucose ratio which will mean that there will not be enough glucose enzymes to accommodate all the yeast enzymes this causing a limiting factor on the number of reactions, hence resulting in less successful collisions. There is no guarantee though that my prediction will be right since there are different factors which could cause a change.
Measuring the CO2:
I will measure the amount of CO2 given off by using a burette rather than counting the bubbles given off. I will do this because it will allow for a higher degree of accuracy. To explain how this will be set up underneath is a diagram to explain.
As the CO2 is produced it will bubble into the burette. An equivalent volume of water will be pushed out of the burette.
Apparatus:
- Clamp Stand
- Bowl
- Water
- Yeast
- Glucose
- Stop watch
- Measuring cylinder
- Conical flask
- Delivery Tube
- Bung
- Burette
Concentrations:
In this experiment I Will use 5 different concentrations of Glucose, and will retry twice for each, thus resulting in 15 different types of answers. I will then get an average for each concentration and plot them on a graph.
The 5 different concentrations I will use are (Glucose cm3):
To ensure that my results are reliable I will replicate the experiment 3 times for each while also working out an average for each, this will help me to produce more reliable results rather than doing each concentration once. I will also start the timing of my results from when the delivery tube is inserted into the Burette.
Method
Make sure the environment is safe to perform an experiment. Do this by clearing the working surfaces of obstructions and making sure the area around your feet is tidy. It is also necessary to wear safety glasses for the duration of the experiment.
Gather the burette, bowl and clamp, and fill the bowl and burette with water accordingly, clamp the burette into place.
Attach the delivery tube to the bottom of the burette, make sure the bung is fixed onto the other end of the delivery tube, then take a measurement of how much water is in the burette.
With a measuring cylinder measure the amount of glucose needed for the first part of the experiment, which is 100cm3, and measure out the amount of yeast needed and pour that into the conical flask, which is 80cm3 with a beaker.
You must then mix the yeast and glucose in a conical flask and place the bung in the top as soon as possible, and start the stopwatch.
After 3 minutes take a recording of how much water is in the burette take the first reading of water from the burette away from the last reading taken and the answer is the amount of CO2 produced.
Repeat this method with different concentrations of glucose.
Results
Analysis:
After completing the results table and graph I don’t think any results were anomalous. If I did have anomalous results, it could have been due to one of many reasons. The first being that of human error and interference, while another could be because of yeast population, this is of cause when the yeast cells start to reproduce by using budding, what happens is the cells slowly start to grow an extra attached cell, when that cell reaches full size it then splits hence creating two of them, thus increasing the population of the yeast. This though is very unlikely due to it requiring time to complete. Other factors that could have affected the experiment are Stirring/Agitation, Temperature, pH or Heavy Metals
Although my experiment didn’t quiet concur with my prediction, I think that my investigation is still valuable since it shows the effects of what different factors can do, to produce anomalous results. The evidence I have I am not sure if they are accurate given the anomalous results.
Evaluation:
In this experiment I think there are many ways in which I could have improved the way in which it was conducted. The first being is using more advanced equipment, such as digital thermometers, freshly made up yeast and glucose, and a computer timing and recording the results. The second is making sure that each time that I preformed an experiment all the containers were cleaned and checked to make sure that the pH was around neutral and no heavy metals were present.
Another way in which this experiment could have been improved is that results were recorded more than 3 times thus giving a more accurate set of results, also using more concentrations of yeast/water could give more accurate results.
Additionally to help to perfect this experiment and get improved and more accurate results, I could do additional experiment, where I could use more glucose concentrations and use more time in which to record them, such as instead of doing minutes 1-5 I could do minutes 1-10 thus resulting in more accurate results.
