2) Dependent variable
The amount of products from each experiment that is water and oxygen.
3) Control variables
These is the variable must stay the same throughout the experiment to ensure a fair test:
Temperature: - It is vital that the temperature remains the same in all the experiments, as this will have a great impact on the results if not.
pH Level:- This is again like temperature in the way that every enzyme has an optimum temperature the same as they have an optimum pH.
Concentration of substrate (H2O2) :-I will use the same amount and the same concentration of substrate for all of the experiments.
Time: - carry out the experiment and record the reading in the same interval of time through out the experiment.
I predict that as I increase the volume of yeast the amount of oxygen produced should increase proportionally, because there will be more active places for a reaction to take place, which will cause more chemical reactions because of successful collisions between the active site of the enzyme and substrate. Eventually, increasing the enzyme concentration beyond a certain point has no effect because the substrate concentration becomes the limiting factor.
Concentration of yeast
Apparatus:
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Hydrogen peroxide (H2O2)
- Boiling tube
- Connecting tube
- 2 Stand
- 2 Clamp
- Beaker
- Little test tube
- Yeast
- Gas syringe
- Small pipette
- Stop watch
- Laboratory coat
- Goggle
- pipette
- Set up the apparatus.
- Make sure the surface and apparatus are completely clean, and ready for the experiment.
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Measure about 10 cm3 of hydrogen peroxide using pipette and pore it into little test tube. The volume of hydrogen peroxide remains constant through out the experiment.
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Measure about 2.5 cm3 yeast using syringe and pore it into the boiling tubes. Increase the volume of yeast by 2.5 cm3 in each new experiment.
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Fix the boiling tube with yeast in the stand using the clamp. Make sure you fix it 45oc.
- Put the little tube with hydrogen peroxide into the boiling tube. Don’t mix the hydrogen peroxide and the yeast till you are ready to take reading.
- Close the boiling tube.
- Fix the gas syringe in a stand using a clamp. Use a gas syringe to measure the oxygen produced. It is specially designed to measure gas and it is made from smooth glass, which will allow all the gas to be collected and easily measured. This makes it very precise and accurate and is easy to use.
- Connect the gas tube and the boiling tube using deliver tube. The rubber delivery tube is used to transport the gas to the gas collector tube to be measured and to minimise the amount of oxygen lost.
- Get ready pepper and pen to write the reading.
- Gets ready the stopwatch.
- Shake gently the boiling tube to mix the hydrogen per oxide with yeast.
- Record the volume of oxygen given off . Keep recording the result till you get the maximum volume.
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Repeat the experiments 3 times for each volume of yeast repeating the experiments will help to produce more accurate results as any inaccuracies in one experiment can be compensated for in the other experiments. Be aware not to contaminate each solution with one another, this will cause inaccurate results.
Interpretation
The rate steadily increases when more substrate is added because more of the active sites of the enzyme are being used which results in more reactions so the amount of Oxygen released in a given time is higher. Once the amount of substrate molecules added exceeds the number of active sites available then the rate of reaction will no longer go up. This is due to the maximum number of reactions being done at once, so any extra substrate molecules have to wait until some of the active sites become available.
When the concentration of Hydrogen Peroxide is increased, the rate of reaction increases at a directionally proportional rate until the concentration of Hydrogen Peroxide reaches about certain volume. If the concentration were doubled, I would expect the amount of Oxygen released to be a figure twice as much.
The theoretical maximum rate of reaction is when all the sites are being used but in reality this theoretical maximum is never reached due to the fact that not all active sites are being used at the same time. The substrate molecules need time to join onto the enzyme and to leave it so the maximum rate achieved is always slightly below the theoretical maximum. The time taken to fit into and leave the active site is the limiting factor in the rate of reaction.
Limitations
- It is impossible to precisely measure out the amounts of Hydrogen Peroxide and yeast each time.
- Some errors are likely to come from measurements. A source of error would be parallax error, which would involve the meniscus
- There is a transfer error. Some amount of yeast and hydrogen peroxide left in the pipette.
- To enable this experiment to be completed as accurate as possible, I will repeat it five times and then use an average of all the results to best plot a graph with a line of best fit.
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Keep all the variables apart.
- The gas syringe only had measurements for 1 whole number this could have affected the results because no decimal places could be used
Ways to Improve experiment.
I will use an automatic pipette, as it is very accurate and precise as it measures every 1000th ml.
Risk Assessment
I will wear a laboratory coat and goggles to protect my eyes, skin and clothes as hydrogen peroxide, and some enzymes can be hazardous and harmful.
Hydrogen peroxide can be corrosive if strong, and an irritant to the skin and eyes. It should not be swallowed. It can corrode clothes and irritate the skin if not washed off thoroughly. Eye protection should be worn and should be handled with care. Contact with the skin should be avoided and clothing should be protected. You should also mop/clean up any spills. All enzymes are potential allergies and can irritate membranes in the eyes or nose (if inhaled). They may also cause an asthmatic attack. Eye protection should be worn and care should be taken when handling. You should avoid handling, inhaling or contact with the skin wherever possible. They must not be swallowed and spills must be mopped up immediately.
Bibliography