Planning
Whilst investigating the following variables must be taken into account otherwise they will affect the results and the investigation will be unable to draw any certain conclusions. List of Variables:
1 Concentration of Yeast Suspension - The more concentrated yeast solution the
more particles of yeast but more importantly this produces more enzymes that will give more collisions without using as much energy. This will therefore increase the rate of respiration.
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Concentration of Glucose – The more concentrated the glucose means the more glucose particles there are, this will result in more collisions and the rate of respiration will increase as there are more glucose molecules for the yeast to feed on and to breakdown to Carbon Dioxide henceforth increasing the rate of respiration.
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Volume of Yeast – If the volume of yeast increases there are more yeast cells in which respiration will occur.
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Volume of Glucose Concentration – If there is more glucose the rate of respiration will increase.
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PH of solution – Yeast use enzymes to respire and enzymes work best at certain a pH.
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Temperature – Similarly enzymes work best at a certain temperature, I will be investigating this during the investigation.
The variable that I am investigating is temperature so the temperature will be altered throughout the course of the investigation. It is essential that the other variables remain constant to make sure only temperature is investigated and nothing else affects the rate of respiration but the temperature.
Prediction
I predict that the rate of respiration will be at its optimum between 35 and 40 degrees centigrade. This prediction is based on the fact that the body temperature of humans and most living organisms is roughly between 35 and 40 degrees. Based on this an enzyme should work best in the conditions the living cell created it for. Even though Yeast is not a human, the temperature of 40 degrees is the body temperature because that is the temperature that enzymes work at their optimum in. Enzymes are also very sensitive to high temperatures, this is due to the shape of the enzyme which is very fragile and sensitive. The enzyme relies on its unique shape to be precise in every detail otherwise the reaction will not work as the enzyme cannot fit into the substrate molecule and react with it. Once temperatures reach around 50 degrees the enzyme starts to lose its shape and become damaged, this means it cannot catalyse as well so the reaction slows down. If the temperatures increase it eventually becomes denatured and the reaction will stop completely because the enzymes are inactive. If the reaction is below 25 degrees the enzymes will not have enough energy to move around and catalyse substrate molecules, therefore the reaction will slow down at temperatures lower than 25 degrees. I also predict that if the temperature is over 50 C or under 10 C the respiration rate will be slow and take too long for any measurements to be made. This is because enzymes lose their shape if the temperature is too high and become inactive or denatured if it is too low. However I will investigate temperatures above 50 C and below 10 C to be more reliable and accurate in this prediction.
Method
For this investigation I will use the following set of apparatus:
- Delivery Tube
- Thermometer
- Boiling Tube (with yeast suspension)
- Plastic Beaker
- Wooden Peg
- Pointed Glass Delivery Tube
- Test-Tube
- Janus Green & Hydrogen Carbonate Indicator & Liquid Paraffin
- Timer
- Test tube rack
Peg
Delivery Tube
Pointed glass
Delivery tube
Plastic beaker to act as water bath
Test tube
Boiling tube with yeast suspension
For the investigation I will fill two thirds of the plastic beaker with water at a certain temperature, the temperature will vary each time the investigation is carried out as it is temperature that is being investigated. I have decided to use temperatures between 10 degrees and 80 degrees, the reasons for this choice are stated a few paragraphs below. 5cm of yeast suspension and 5cm of glucose is put in the boiling tube at a concentration that will remain the same throughout the investigation. The solution is then coated with liquid paraffin so no oxygen can enter the solution, this is done so the yeast can respire anaerobically (without oxygen) as opposed to aerobically. The concentration of yeast and glucose will remain 20% throughout the investigation because they are controls. The boiling tube is then placed in the plastic beaker that is filled with water at a certain temperature. Janus Green is then put into the solution, Janus Green is an indicator that detects and measures oxygen levels, if the colour of the indicator is pink then there is no oxygen present. Once the colour changes to pink the experiment is ready to begin as there is no oxygen in the solution and so the yeast cannot respire aerobically.
The boiling tube is covered and attached to the delivery tube which is placed into the test-tube with the pointed glass touching the surface of the solution. The solution used will be another indicator called Hydrogen Carbonate Solution this will identify the presence of Carbon Dioxide that will diffuse into the hydrogen-carbonate solution. The wooden peg is attached to the delivery tube to hold it in place and make sure the pointed glass lies on the surface of the hydrogen carbonate solution. When the experiment is ready to start, I will count how many bubbles or carbon dioxide appear in the hydrogen carbonate solution. The hydrogen carbonate solution is also effective as it will also measure the amount of carbon dioxide in the solution. If the hydrogen carbonate turns yellow the solution is more acidic and there is more carbon dioxide in the solution. The amount of bubbles will be measured every minute, this will be carried three times and an average taken for the three results, this is for reliability and accuracy.
For health and safety I will wear a protective lab coat and safety specs.
I have already carried out a preliminary experiment. The results for the preliminary experiment are written below:
Although there were only a few results recorded I learnt a lot from the preliminary experiment it was very useful as it enabled me to make decisions such as equilibration time, concentration of glucose and yeast, volume of glucose and yeast, temperature range and time allocated for counting bubbles. The preliminary experiment showed that there was need for improvement in the measurements and how the results were collected. In thirty seconds there were two bubbles of carbon dioxide when I used 20% yeast concentration and 10% glucose concentration at a temperature of 30 C. Two is a low number for this type of experiment and if my prediction for temperature of enzyme activity is right then four must be one of the highest number of bubbles I should expect to see. Therefore I must increase the time allowed for counting bubbles otherwise there will be a very limited range and the results will be unreliable and inaccurate. I have decided to increase the time allowed for counting bubbles to a minute but not more because the experiment will take too long especially if I am to carry it out three times for each temperature. To make up for lack of bubbles and rate of respiration I have decided to increase the glucose concentration to 20% hoping that this will affect the rate of respiration and the amount of bubbles. My preliminary experiment also helped me to decide other factors such the time to equilibrate and the temperature range. With the lack of bubbles the results will not be so clear and exact so I have decided to limit the range slightly, the temperature range will be form 10C to 80C with measurements made every 10 degrees. I have kept the temperature range quite wide for reliability and for extra support to the conclusion. The preliminary experiment also helped me to understand how to set up the experiment most efficiently and also clarified a few points on the experiment that I was initially unsure of.
