Yeast results:
A Table to show 10 results from 10 students showing the rate of anaerobic respiration in yeast against time at 20 ºC
A Table to show 10 results from 10 students showing the rate of anaerobic respiration in yeast against time at 35 ºC
A Table to show 10 results from 10 students showing the rate of anaerobic respiration in yeast against time at 50 ºC
Averages:
Results for the bubble length at each 5 minute interval added together
10 students (number of results recorded)
= Average
For example; at 20 ºC, the average5 minute result is: 22
10 =2.2
A table to show the average results of bubble length (mm 1d.p) at 5 minute interval in beakers of 3 different temperatures; 20 ºC, 35 ºC and 50ºC
My average results suggest that 25 minutes in the water bath at 20 ºC, the average bubble length is 6.2 mm, while in the water bath at 50 ºC the average bubble is 24.7mm, almost four times the length. This indicates that the higher the temperature of water bath, the longer the bubble length in the fermentation tube. They also suggest that the bubble length lengthens most rapidly within the first 15 minutes, and the reaction gradually slows down in the subsequent times.
For example, between 10 and 15 minutes at 50 ºC, the bubble length grows from 13.5mm to 18.5mm, expanding 5.0 mm, although at 45-50 minutes at 50 ºC, the bubble length only grows from 33.2mm to 34.2mm, only expanding 1.0mm.
Graph
Gradients of the average length of bubble at 5 minute intervals in water baths of temperatures 20 ºC, 35 ºC and 50 ºC:
y2-y1 (length of bubble: mm)
----------
x2-x1 (Time: minutes)
Gradients:
Gradient= y/x = bubble length/time
For example, 50 ºC initial rate, 22/15 = 1.46 mm/min (rounded to 1.dp) = 1.5mm/min
A table to show the gradients of the average bubble length (mm) at different temperatures during 3 different stages of the experiment
My graph shows that at higher temperature, the reaction occurs at a faster rate than when the temperature is lower. From my AS study of enzymes, I know that enzymes catalyse ‘every metabolic reaction’ within living organisms, including controlling respiration. When enzymes are catalysing a breakdown of a substance, for example the enzymes in yeast break down the sugar solution; the substrate binds itself in the active-site forming an enzyme-substrate complex, the bonds are weakened so the substrate molecule can break apart more easily. While if an enzyme is joining two substrates together, they are attached to the enzyme, bringing the molecule closer together so a bond forms easier.
There is a distinct difference between the initial gradient of the Co2 production/ bubble length during the three yeast solutions of different temperatures. At 20 ºC, the gradient is 0.5 mm/per min, while at 50 ºC, the gradient is 1.5 mm/per min. This is due to the fact that the enzyme controlled reactions of the yeast are identical to any chemical reaction- the more kinetic energy provided; the more rapidly the reaction will occur up to a point. Being a catalyst, after the reaction has occurred, the products are released and the active site remains unchanged to carry out further reactions.
The measure of kinetic energy is approximately equal to the temperature applied to the system. Brooklyn Academic agrees and stated that ‘the kinetic energy of the molecules can be converted into chemical potential energy’ when molecules have collided enough times with the correct amount of energy. This chemical potential energy can help the system achieve the activation energy and more reactions can occur. The 50 ºC water bath of yeast solution had a higher amount of kinetic energy due to the increased temperature. The higher the effect of kinetic energy to a system, the more chemical energy the substrate has, which gives it enough energy to collide with the enzymes active site and reach the activation energy. Also, there will be a higher amount of vibration of the particles so more collisions of particles so more reactions will occur.
The vibrations of the particles in the water baths of lower temperatures will be less, thus less substrate would collide with the enzymes active site with enough energy for the molecules to break.
The gradient of each reaction in the water baths of different temperatures are steepest at the beginning, for example; the Co2 production/ bubble length in the water bath at 35 ºC grew most within the first 5 minutes, the gradient is 1.0mm/per minute, while at 30 minutes, the gradient has decreased to 0.2mm/per minute. This gives evidence that after a certain period of time, the rate of respiration by the yeast solution has shoed down in each water bath. This is due to the fact that there is more substrate available for reaction and also there being more available active sites free for the substrate to bind at the beginning of a reaction. After a period of time, the rate of respiration decreases after the substrate molecules are used up and many of the active sites are full.
Although the carbon dioxide production increases fastest by the yeast solution in the beaker of water at 50 ºC, by 50 minutes, each gradient was 0.7mm/per min, thus showing that the reaction has slowed down for each solution of yeast in the different temperature water baths. This also indicates that at 50 minutes, while anaerobic respiration was taking place producing ethanol, the concentration of this toxic substance grew too high and began to kill the yeast cells, thus level of respiration and production decreased.
From A2 study of populations and interactions, this is what I would expect. The lag phase was during the time when I was trying to accurately reach the correct temperature in the test tube before beginning the experiment in the fermentation test tubes. This was when little respiration was occurring as the yeast is adjusting to the conditions; the log phase is when the gradient increased as the yeast begins to respire rapidly. The stationary phase is approximately 50 ºC in the experiment, as the graph indicates that the CO2 production is gradually slowing down and the graph then begins to level out. The gradients are less steep at this point, for example, at 20 ºC the gradient is 0.2mm/per min. This is due to the end products of respiration and lack of nutrients in the solution. Therefore yeast can not respire anymore.
A diagram showing the growth curve at various stages
Initially, the yeast solution respired aerobically; this gives off the highest yield of Co2 as the pyruvic acid molecules are completely broken down into carbon dioxide and more energy, thus the gradients for each reaction of the yeast solution in a beaker of a different temperature are steepest at the beginning of the reaction.
C6H12O6 + 6O2 → 6CO2 + 6H2O+38 ATP
Aerobic respiration equation – 6 moles of Co2 forms.
C6H12O6 → 2C2 H5OH + 2CO2+ Energy
Aerobic respiration (fermentation0 equation- 2 moles of CO2
The gradient of the 50 ºC solution of 0.9mm/per min is because most of the solution has been used up in respiration before this point as it previously has been the most rapid experiment, also, the enzymes may have become denatured due to the high temperatures, as the below diagram shows that optimum temperatures for an enzyme to work at Is at approximately 38 ºC.
A diagram showing an enzyme rate of reaction at different temperatures
Some aerobic respiration was carried out by the yeast solution when the fermentation tube was first overturned into the test-tube as some oxygen was caught in the tube. After the oxygen was used up in aerobic respiration, the yeast will begin to respire aerobically, releasing ethanol and carbon dioxide. This bakers yeast has been adapted through artificial to work well in condition which allows CO2 to be respired, which is the desired feature for bread to rise.
Z test
Null hypothesis= There is no significant difference between the means of the samples tested.
I will use this formula:
Assuming that there is no significant difference between means, therefore D= 0.
To find the difference between the means for the 2 temperatures 20ºC and 35 ºC, I will use the constant time- 25 minutes.
The variance of each sample=
To prove whether the above statement is also correct for the difference between means for 35 ºC and 50ºC, I will use the z test for the results at 25 minutes.
If the Z number is more than 1.96 or less than -1.96, I will reject my hypothesis, as between 1.96 and -1.96 it is the 5% confidence interval region and I can accept the null hypothesis that there is no significant difference between my means.
Difference between means of 25 ºC and 35 ºC= -3.98(2d.p). This is less than -1.96 therefore I will reject my hypothesis that there is no significant difference between means of the results.
The difference between means of 35 ºC and 50 ºC= -0.85(2d.p). This figure is out of the rejection of the critical value table, therefore I will accept my null hypothesis that there is no significant difference between means of the results.
A diagram showing an enzyme rate of reaction at different temperatures
This diagram illustrates my findings from the z-test. At approximately 35 ºC and 50ºC on the graph, the enzyme activity is very similar. At 35ºC, the enzymes and substrates are not colliding at the maximum rate so there are still free active sites for the enzymes reaction to occur. While at temperature, therefore less substrates are able to fit into the changing tertiary structure of a protein is not very stable so can unravel as energy of the molecules in the enzymes globular structure. this cause the protein to unravel and also the active sight to change shape, thus the substrates which were before able to react, are now unable to fit and hence the reaction slows down until it discontinuous.
35 ºC and 50 ºC are both slightly away from the optimum temperature for the enzyme to react; therefore means are also not significantly different. At 20 ºC, there are not a lot of collisions due to the low kinetic energy provide, therefore the reaction is slow and there is a significant difference between the means of this temperature and 35 ºC.
Accuracy of experiment
Although the results seemed quite accurate I believe that mistakes could easily have been made and that the results are not as accurate as they could have been. This is because each temperature was measured by a different student in the class group and that each student could have made a slight error either in calculations or by human error (e.g. counting the amount of gas produced).It has not been possible for me to take into account the amount of carbon dioxide which was absorbed by the solution; this has an effect on the result, as my results were different to reliable evidence which I found about what the optimum temperature for yeast is. The anomalous results were determined by comparing figures and highlighting those which are significantly different. There were no apparent anomalies in the average results, however a few minority within the 10 students’ results, this suggests that the anomalies in results weren’t significant enough to make a prominent mark on the average calculations, however the minor anomalies could be explained by the inaccuracy of results and that the reaction could not be totally accurately controlled with the apparatus used.
Anomalies might have occurred as students were not measuring the bubble from the same point-bottom of the meniscus and also may have different ideas of approximation- human error as one student may measure the bubble up to the next whole number, while another student may round down. If this was the case then results would be untrue and therefore our group results combined together would be formed on the trust and believe that each student had completed the experiment accurately and correctly which would mean the result were extremely unreliably.
Evaluation
To make sure that the results were as reliable as we could make them; we calculated the mean of 10 results at 5 minute intervals.
Although the results seemed quite accurate I believe that mistakes could easily have been made and that the results are not as accurate
as they could have been. This is because each temperature was measured by a different student in the class group and that each student could have made a slight error either in calculations or by human error (e.g. counting the amount of gas produced).If this was the case then
results would be untrue and therefore our group results combined together would be formed on the trust and believe that each student had
completed the experiment accurately and correctly which would mean the result were extremely unreliably.
Apparatus used were not 100% accurate. Using a graduated capillary tube will increase accuracy therefore reliability of the experiment as the graduations are smaller and more precise than using a 30cm ruler which is only to +/-0.5mm and I will be able to get better results from the volume of gas collected. Also, fewer errors will occur than while reading ruler through three panes of glass as light will bend distorting clear view of bubble in the fermentation tube and become dependant on human judgement and sight.
To obtain more reliable results and if I were to conduct the experiment again I would want complete continuity with preparations, maybe arranging 'sets' of substances to create several solutions of glucose beforehand and adding the yeast separately at a set time but not actually activating the yeast until necessary so as to prevent any solutions getting a 'head start' over the others. This would ensure that all the preparations are the same and would give continuity. I would want to be more strict and thorough with preparing solutions and mixing them up. I would want each one to be thoroughly acclimatised to the surroundings and had the same amount of glucose and the same activating and mixing time. This would help give more reliable results throughout.
Another alteration to my investigation would be changing the way in which I collected the gas. This would increase the accuracy of the results if
they had a human error. This is because the measuring cylinder we used may not have been filled at a correct graduation mark and therefore
the results would have been untrue as there would therefore have been human error of the results + or- a graduation mark.
The yeast is converting sugar to ethanol and carbon dioxide- which causes the foam layer of carbon dioxide. This causes difficulty when measuring the bubble length with a ruler. To improve it, pipette solutions from under the foam layer into fermentation tube- push it down the side of the tube to prevent foam bubbles forming. This will increase reliability as the yeast solution will have its rate of reaction measured.
Controlling 3 solutions of different temperatures consistent is very hard to keep up, to improve its best to use a thermostat water bath and cooler. This increases reliability as it is electronically controlled so able to ensure that the temperatures are stable, making the experiment more accurate and fair. Also safer not having to leave a Bunsen burner on while rushing to record the length of bubble.
If I were to further investigate this experiment and my results, I would probably want to calculate the point where the enzymes begin to denature for respiration in yeast. I could also examine the change in rate between the intervals to determine validity and continuity. I would also have taken more results at each temperature interval as to increase the depth and accuracy of the results and therefore would help in achieving a better graph with a stronger correlation.
Bibliography/References
AS-Level Biology, OCR Revision Guide CGP Ltd 2003
Biology 2 – Cambridge Advanced Sciences. Published 2001 Cambridge University Press.
The Penguin DICTIONARY OF BIOLOGY. Published 1992 M.Abercrombie
SCHAUM’S A-Z SERIES, ed. Bill Indge, 2003
http://faculty.ircc.edu/faculty/tfischer/images/bacterial%20growth%20curve.jpg
http://support.dundas.com/OnlineDocumentation/WebChart2005/ZTest.html
