The equation for aerobic respiration is:
Glucose + Oxygen Carbon Dioxide + Water +Energy
Anaerobic respiration is what happens when there is no oxygen available at all. “Anaerobic” means “something without oxygen” and it is not the best way to convert glucose into energy. Anaerobic respiration does not produce nearly as much energy as aerobic respiration, but it is useful in emergencies.
The equation for anaerobic respiration is:
Glucose Energy and Lactic Acid
Anaerobic respiration is performed by yeast while making bread and beer, which is known as Fermentation.
The equation for fermentation is:
Glucose Alcohol + Carbon Dioxide (+ Energy)
In bread making, as the yeast gets to work, it’s the Carbon Dioxide which is given off that makes the bread rise. In brewing, the alcohol given off is the most important bit, but the Carbon dioxide makes it fizzy.
When all the oxygen is used up, the yeast keeps on respiring. The glucose is used up. Due to a lack of oxygen, the products produced are carbon dioxide and ethanol. Therefore the overall process for fermentation is: Glucose Carbon Dioxide + Ethanol + Energy C6H12O6 2CO2 + 2C2H5OH + 84kj There is more energy in the anaerobic reaction because the energy that the yeast needs from glucose is locked up in the ethanol. After the concentration of ethanol reaches 12%, the yeast is killed and fermentation stops.
The Lock & Key Theory Emil Fischer originated the lock and key theory in 1894. It states that it takes the correct key to open a lock. It takes a correct enzyme to bond to the substrate and catalyse its reaction. An active site of an enzyme is made up of a binding site and a catalytic site. To understand the experiment clearly I feel that it is necessary to explain the enzyme theory. Enzymes are large proteins that speed up chemical reactions. They bring together a small number of amino acids to form the active site, or the location on the enzyme where the substrate binds and the reaction takes place. Enzyme and substrate fail to bind if their shapes do not match exactly. This ensures that the enzyme does not participate in the wrong reaction. The enzyme itself is unaffected by the reaction. When the products have been released, the enzyme is ready to bind with a new substrate. This description of the enzyme is known as the lock and key method. Koshland said that the shape of an active site of an enzyme does not have to be the same type of the substrate. This was called the Induced Fit Theory. The Collision Theory In order for a reaction to take place, the reacting substances must collide and energy, called the activation energy, must be reached. If the collision between the particles can produce a lot of energy, then a reaction can take place. For the collision to take place, the particles must collide fast enough and in the right direction. The higher the number of collisions, the faster the rate of reaction. Increasing the concentration of a substance, will increase the amount of collisions. I also predict that by doubling the concentration of sugar solution would double the reaction. Increasing the concentration means that there are more enzymes in a given space, therefore more active sites would be available for a reaction to take place in.
My method:
- Firstly, I will set up my equipment
- I will measure out 10ml yeast with a measuring cylinder and place into the boiling tube
- I will measure out my 20% sugar concentration (10ml) in measuring cylinder which is undiluted
- Then I will fill my first beaker with tap water
- In the first beaker I will place the rubber tubing in which has a small glass tube at the end
- I will fill the other measuring cylinder to the top with tap water and insert it into the beaker and place over the glass tube
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I will fill the second beaker with hot water and make sure it is at 40
- I will then place the sugar solution into the boiling tube and put on the rubber bung to seal the boiling tube from Oxygen
- I will start the stop-clock for 2 minutes
- Then I will get a ruler and measure how much Carbon Dioxide has been given off by measuring how much the water has gone down in the measuring cylinder
- I will record the result in centimetres
- I will now test the different concentrations of :
15% (7.5ml sugar solution + 2.5ml water)
10% (5ml sugar solution + 5ml water)
5% (2.5ml sugar solution + 7.5ml water)
0% (0ml sugar solution + 10ml water)
- For each of these different concentrations a set of two repeat results will be tested and recorded
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Then I will take averages of three results combined per concentration and work out the volume of carbon dioxide by using the formula for cylinders
Preliminary testing
I carried out preliminary testing once I found out what the set task was because I thought that these would give me an insight into what I am trying to find out. I decided to trial a large range of measurements to see which were the most suitable. I tested a range from 0% to 40% but from my actual time of the experiment I found it was time consuming and it would be more time efficient if I kept the range to 0% to 20%, also it was easier to work out. I realised I needed 5 results in order to plot a suitable graph so I would maybe increase each step at certain intervals throughout my 0% to 20% concentrations range. I then decided that the overall concentration of sugar solution and water would amount to 10ml (20%), instead of 20ml (40%) which I used in preliminary workings. I also tried out different timings for the experiment to be carried out in. I tried setting the timer for 1 minute and then for 3 minutes. I decided that from my preliminary testing, 1 minute wasn’t long enough for a sufficient amount of carbon dioxide to be produced. Also, after 3 minutes, there was often a large amount of carbon dioxide being produced and this was too much for the 10ml measuring cylinder. So I came to the compromise of choosing a time between 1minute and three minutes, which is 2minutes. My preliminary tests helped me choose appropriate and a sufficient range of values and measurements. Another aspect from my preliminary work that helped me decide upon a suitable volume for the yeast was because if too much yeast was placed into the boiling tube, it would bubble during respiration and the froth would travel up the tubing causing further problems. So from my preliminary work I decided 10ml yeast each time was a suitable volume added to the volume of the concentration of sugar and water in the boiling tube. I also found out from my preliminary results that a gas certainly was produced during the respiration and I predicted it to be carbon dioxide. To prove my prediction I tested the gas with limewater to see if it turned the limewater milky. The limewater went a cloudy milky colour proving that carbon dioxide is a product of respiration.
Here are my preliminary results:
To show my results graphically I have produced a sketched graph for my preliminary results:
8. 0% 0ml sugar solution in 20ml water
7. 10% 5ml sugar solution in 15ml water
6. 20% 10ml sugar solution in 10ml water
5. 40% 20ml sugar solution in 10ml water
4.
3.
2.
1.
0.
1 2 3
My measurements will consist of a suitable sufficient range of results. I will measure the concentration of the sugar solution and water by using a measuring cylinder and measuring in millilitres. My smallest measurement of sugar solution will be 0ml and my highest will be 10ml. To add to the solution and make up the concentration I will add tap water as a dilutor. I will measure the water in millimetres using a measuring cylinder. My smallest measurement of water will be 0ml, and my highest will be 10ml. I will take 5 measurements and each will increase by2.5ml steps. I will use a ruler to measure the height in millimetres of the carbon dioxide produced. I will measure the volume of yeast in millimetres using a measuring cylinder. The yeast will always be measured out as 10ml every time. I will observe the temperature of the hot water making sure it does not cool down too much remaining at 40. I will also observe the time of two minutes on the stop-clock. I will take repeat measurements to make sure my experiment is accurate. I will take two extra repeat measurements for each concentration.
My concentrations:
- 20% is 10ml sugar solution and 0ml water
- 15% is 7.5ml sugar solution and 2.5ml water
- 10% is 5ml sugar solution and 5ml water
- 5% is 2.5ml sugar solution and 7.5ml water
- 0% is 0ml sugar solution and 10ml water
I used my equipment with precision and when measuring out the concentrations in ml inside a measuring cylinder I was careful and accurate. Also while I measured the height of gas produced in the measuring cylinder with a ruler, I measured accurately to the nearest millimetre to make sure my measurements were correct in order to have accurate calculations to find the average volume later on. By using a ruler to measure in centimetres and the nearest millimetre, it was an advantage on using the measuring cylinder’s scale in ml that was actually collecting the gas because mm are more accurate than ml. Furthermore, while carrying out the repeat measurements, I noticed that they weren’t that far apart, which suggests my results were consistent and reliable due to the accurate measuring.
My table of results:
Now I will calculate these results to find the volume of the carbon dioxide produced in the measuring cylinder by using the volume of a cylinder formula below:
I measured the radius of the measuring cylinder with a ruler and it was 1.75cm.
rh
e.g. x 1.75 x 2
=19.24cm
Once I have worked out the volumes I will take averages for each concentration by adding up all of the 3 tries and then dividing the number by 3.
Calculations:
20% concentration
try 1- x 1.75 x 2 = 19.24cm
try 2- x 1.75 x 2.7 = 25.98cm
try 3- x 1.75 x 2 = 19.24cm
19.24+25.98+19.24 = 21.49cm
3
∴average = 21.49cm
15% concentration
try 1- x 1.75 x 1.5 = 14.43cm
try 2- x 1.75 x 1 = 9.62cm
try 3- x 1.75 x 2 = 19.24cm
14.43+9.62+19.24 = 14.43cm
3
∴average = 14.43cm
10% concentration
try 1- x 1.75 x 1.5 = 14.43cm
try 2- x 1.75 x 1 = 9.62cm
try 3- x 1.75 x 1 = 9.62cm
14.43+9.62+9.62 = 11.22cm
3
∴average = 11.22cm
5% concentration
try 1- x 1.75 x 1 = 9.62cm
try 2- x 1.75 x 0.8 = 7.70cm
try 3- x 1.75 x 0.7 = 6.73cm
9.62+7.70+6.73 = 8.0cm
3
∴average = 8.0cm
0% concentration
try 1- x 1.75 x 0 = 0cm
try 2- x 1.75 x 0.2 = 1.92cm
try 3- x 1.75 x 0.1 = 0.96cm
0+0.96+1.92 = 0.96cm
3
∴average = 0.96cm
Now I will format my averages into a table so the patterns can be seen more clearly.
From my final results table, I can use the average results to plot a graph of results.
From my results I can identify a trend of a straight line gradient. My graph shows that as the concentration of sugar solution is increased, the volume of carbon dioxide also increases. The fact that carbon dioxide is being produced, proves that respiration is taking place. The continual increase of carbon dioxide means that the rate of respiration increases as the concentration becomes less dilute and stronger. I can see that the rate of respiration is at its slowest when there is no sugar solution present to aid the process and the volume of carbon dioxide produced barely reaches 1cm. However, my graph also shows me that respiration can take place in a very small amount and at a very slow rate without any sugar solution to act with the yeast. When the concentration was of 20%, which was full sugar solution and yeast, the volume of carbon dioxide is very high at 21.5cm. There is a big difference between the rate of reaction of 0% compared with the 20% concentrations. This definitely suggests that concentration, has a large impacting affect on the rate of respiration. The concentration of a solution can speed up or slow down the rate of respiration depending on how concentrated the solution is. In the case of my experiment, the strongest concentration speeded up the rate of respiration while the weakest concentration was very slow in producing carbon dioxide thus, showing that the rate of respiration was much slower. So the trend is clearly evident from the results I obtained.
I can explain my results by relating to collision theory.
Collision theory
“For a reaction to occur particles have to collide with each other. Only a small percent result in a reaction. This is due to the energy barrier to overcome. Only particles with enough energy to overcome the barrier will react after colliding. The minimum energy that a particle must have to overcome the barrier is called the activation energy, or Ea. The size of this activation energy is different for different reactions. If the frequency of collisions is increased the rate of reaction will increase. However the percent of successful collisions remains the same. An increase in the frequency of collisions can be achieved by increasing the concentration, pressure, or surface area.”
Collision theory explains reaction rates because the rate of reaction depends on how often and how hard the reacting particles collide with each other. The particles have to collide in order to react and their collision must be hard enough as well. More collisions increase the rate of reaction. Concentration increases the number of collisions.
When the solution is made more concentrated it means there are more particles of reactant knocking about between the water molecules, which makes collisions between the important particles more likely.
When the concentration of sugar was increased, the rate of reaction increased. Adding a higher concentration of sugar increased the sugar particles in a given space. As the mixture was heated, the sugar particles will begin to move. Due to a lack of space, this would result in collisions. Thus the rate of reaction increased in my experiment, resulting in the yeast respiring more therefore giving off more carbon dioxide gas, which, measured a larger volume in the measuring cylinder.
The Lock & Key Theory Emil Fischer originated the lock and key theory in 1894. It states that it takes the correct key to open a lock. It takes a correct enzyme to bond to the substrate and catalyse its reaction. An active site of an enzyme is made up of a binding site and a catalytic site. To understand the experiment clearly I feel that it is necessary to explain the enzyme theory. Enzymes are large proteins that speed up chemical reactions. They bring together a small number of amino acids to form the active site, or the location on the enzyme where the substrate binds and the reaction takes place. Enzyme and substrate fail to bind if their shapes do not match exactly. This ensures that the enzyme does not participate in the wrong reaction. The enzyme itself is unaffected by the reaction. When the products have been released, the enzyme is ready to bind with a new substrate. This description of the enzyme is known as the lock and key method. Yeast has its own enzyme that when heated at 40 works best because it is like body temperature so the yeast is works faster when heated and is more likely to collide with the sugar and react causing respiration.
My results obtained from the experiment support my original prediction, as before my investigation I thought that as the concentration of sugar is increased, the rate of respiration will increase. So as higher concentrations of sugar are in the boiling tube, it will react with the yeast and respire more giving off more carbon dioxide. After looking at all the experiments data collection I thought I would see a gradual incline in the volume of the measuring cylinder as the concentration of sugar solution is increased. I thought this because the stronger sugar solution will be more for the yeast to react and respire with more, at a faster rate. I also predicted that by doubling the concentration of sugar solution would double the reaction. Seeing as there is no oxygen present in my experiment, I predicted that anaerobic respiration would take place. Evidence of no oxygen being present is the fact that the yeast and sugar concentration was sealed in a boiling tube with a rubber bung. So from my results, I have found that they matched my prediction. So my prediction was correct and my results prove this showing the increasing carbon dioxide given off during the respiration as the concentration of the solution was increased. I noticed from my work that respiration took place at a faster rate as concentration was increased. A scientific reason that backs up my findings is the explanation of collision theory.
Evaluation
Overall, my experiment went considerably well. The procedure I used was appropriate because it let me find out if changing the concentration of sugar solution had a significant effect on the rate of respiration of yeast. My method tested my prediction as I had initially thought that there was a direct link between increasing the concentration equalling an increase in the rate of respiration in yeast. The method I used was accurate because I took time and precision while measuring out my volumes and concentrations to make sure it was fairly measured. Also, I was very careful planning my experiment making sure my test was the fairest most possible. I controlled the temperature, the volume of yeast, the species of yeast, the concentration of yeast, and used that same equipment for each different test in my investigation. Also, while measuring and taking my results from the amount of air space in the measuring cylinder, I was very accurate by measuring to the nearest millimetre on the ruler. It was a more accurate way to measure the gas produced with a ruler as millimetres could be measured instead of using the actual measuring cylinder, which only measured in millilitres. By measuring to the nearest millimetre instead of centimetre, my results were more accurate and precise, which made them more exact as I made the calculations using a formula of a cylinder to find out the volume. When I worked out the calculations for the volume of carbon dioxide produced, I took them to two decimal points, which meant my answers were in 3 significant figures, which is even more accurate.
My range of values were practically sufficient, however, they could have been improved by adding different intervals such as going up in steps of 2ml instead of 2.5ml throughout the 0%-20% existing range. For example, 0ml, 2ml, 4ml, 6ml, 8ml, 10ml etc. These values would have results closer together which would have shown the increasing rate of respiration more easily. I found that I was able to carry out enough repeat measurements in the time I had to complete the experiment. I took 3 sets of measurements, which I thought was efficient as none of my results seemed to be “odd” and did not need to be repeated again.
My results are consistent as they follow the trend of increasing the rate of reaction as the concentration is increased. So I believe my results are reliable because the repeat readings are all quite similar and none of them are totally off track or “odd”. My results show a consistent trend which also makes me believe my results are reliable seeing as they all follow the same pattern. There are no “odd” results on my graph that stand out or that are located far off my line of best fit that I drew.
During my experiment there were some minor problems I encountered, however, these did not effect my results as they were minor set backs, which I was able to easily sort out. Firstly, once I had poured the hot water into the beaker, it was at 40, but as the test carried on, a small number of degrees were lost as the water cooled down. My quick solution for this was to top the beaker up with a small amount of hot water. I think a more improved method for avoiding water loss would have been to insulate the beaker by encasing the outside of it with paper towels and bubble wrap to prevent heat loss. Another problem that I encountered was that the bubbles of carbon dioxide that were being produced, were becoming trapped in the rubber tubing leading to the other beaker. This was due to air expansion. So I had to shake the rubber tubing every so often to release these trapped bubbles. An improvement on this could be to
The seal between bung and test tube may not be air-tight. This would cause the gas produced by the reaction to escape through the leak and therefore there would be only few bubbles if any. To prevent this you could smear a layer of Vaseline around the edge of the join between bung and tube. This would fill any cracks and stop the leak. If the temperature of the water was varying then we could use an insulative material as a cover for the beaker with a hole for the test tube in the centre. The depth of the delivery tube in the beaker would affect how many and how quickly the bubble were released as the more pressure pressing down on the tube with increasing depth would make it harder for the bubbles to escape.
The evidence of which I obtained I believe is sufficient enough to support a firm conclusion as I proved what was set out in my investigation. The task set was to investigate the effect of changing the concentration of a sugar solution on the rate of respiration of yeast. My results prove that the task was answered by my findings that were the rate of respiration in yeast increases as the concentration of sugar solution is increased. So the conclusion to my investigation is that the higher the concentration of a solution, the faster the rate of reaction will be and will take place in any given time such as 2 minutes like in my investigation. So, the rate of respiration would carry on increasing as higher concentrations were added. However, if the experiment had of continued then there would be no more bubbles of carbon dioxide as all of the material has reacted after a certain amount of time.
Conclusion The rate of respiration increases gradually before reaching its peak. It then decline steeply as all of the material has reacted.
Other groups in my class that performed the same experiment had very similar findings to myself. Below is an example of another pupils results:
Therefore these results are very similar to my own and they agree with my results. So the fact that other people’s results agree with my own compliments the reliability of my results. Also information from texts such as my Biology GCSE Revision Guide has similar explanations to myself about respiration and also software such as Encarta Encyclopaedia CD-ROM Package . "Respiration," Microsoft® Encarta® 98 Encyclopaedia. © 1993-1997 Microsoft Corporation. All rights reserved. That segment of text tells us more about the scientific facts towards this experiment.
(Refer back to my results table to compare)
Further experiments to extend the investigation could be to investigate another factor such as temperature. I could investigate the effect of changing the temperature on the rate of respiration in yeast. I would have to keep the concentration of the sugar solution at a constant because, as I have learned from the experiment above, concentration is a key factor to the rate of respiration. I would also have to keep the same species, concentration and volume of yeast. The variable I would change would be the temperature and my range of values could be 0, 10, 20, 30, 40, 50.
My equipment would include:
- 2 x 10ml measuring cylinders
- Boiling tube
- Delivery tube
My prediction for this experiment is that the volume of the measuring cylinder will increase according to the temperature. As the temperature gets hotter the volume in the measuring cylinder will increase. But as the temperature reaches 40’c to 45’c we will see that the volume in the cylinder has started to fall as it is starting to denature. After looking at all the experiments data collection you will see a gradual incline in the volume of the measuring cylinder.
Scientific reason: Increasing the temperature of the substrate can increase the number of collisions. The Collision Theory In order for a reaction to take place, the reacting substances must collide and energy, called the activation energy, must be reached. If the collision between the particles can produce a lot of energy, then a reaction can take place. For the collision to take place, the particles must collide fast enough and in the right direction. The higher the number of collisions, the faster the rate of reaction. The effect of the temperature upon the rate of reaction can be predicted by using the collision theory.
I predict that increasing the temperature would speed up the reaction. This is because when the mixture of glucose and yeast is heated, the molecules would gain energy and move faster and travel a greater distance, which would result in more collisions. Also, the particles are moving faster therefore a large proportion of the collisions would exceed the activation energy, thus speeding the rate of reaction.
I must be careful while handling the hot water in the aspect of my own safety.
