I also predicted that the rate of activity would decrease when the temperature got beyond a certain point, which is shown on the sample graph I drew for my prediction. This is exactly what happened during the actual experiment.
I also correctly predicted approximately where the rate of enzyme activity would peak, and where it would begin to decrease.
The sketched line of best it that I drew for my prediction accurately resembles the actual line of best fit on the graph I drew displaying the results of the investigation. This line shows the increase in enzyme activity as temperature is increased and the decrease in enzyme activity after optimum temperature.
This means that my results have proven my prediction to be correct.
Explaining What I Have Found Out
Where was the optimum temperature and why is it the optimum temperature?
My results and my line of best fit show that the optimum temperature for enzyme activity is around 37°c to 40°c. Somewhere around 37°c is the internal body temperature of most mammals, meaning that enzymes are working at their optimum efficiency, when they are working inside the mammal they belong to. If the optimum temperature for a particular mammal’s enzymes were above or below the internal temperature of the mammal’s body, the chemical reactions responsible for digesting that mammal’s food would be much slower and less efficient. If enzymes were not present or could not work as fast as they do, life would grind to a complete halt. Enzymes are essential for speeding up vital biochemical reactions needed for many organisms to survive.
So why do enzymes work best at higher temperatures?
Enzymes are nature’s biological catalysts. Digestive enzymes are designed to break up food. When food is eaten, most food molecules are long and complex, and are not yet small enough to be absorbed into the bloodstream. For an enzyme to break down a large, insoluble food molecule (such as starch, fat or protein) it must have a specific shape, depending on which type of food molecule it is designed to break down. Enzymes work by randomly bumping into food molecules, as they move around. An enzyme’s shape is such that if it comes into contact with the right food molecule (it’s substrate), the molecule will fit like a key into a specifically designed shape on the surface of the enzyme (the lock). When the enzyme moves away again, the part of molecule being held by the enzyme, will be snapped of, and becomes a smaller, simpler molecule. We call this process the “Lock and Key” process:
This process happens again and again, until all of the food molecules have become small enough for absorption. Enzymes do not get used up or consumed during this process, they just increase the rate of reactions.
At lower temperatures all particles (including the hydrogen peroxide used in our investigation), move about relatively slowly, meaning that they do not bump into each other (or enzymes) as often as they could, so the rate of chemical reactions is slower. Cooling or even freezing does not destroy the enzymes, it only slows down the activity of their substrates.
When particles are subjected to higher temperatures however, they move about much faster. When under higher temperatures, the hydrogen peroxide molecules have more kinetic energy (they move about quicker), so they bump into enzymes much more often. The more often enzymes come into contact with food molecules, the quicker all the molecules are digested.
This science is clearly illustrated by my graph, as the rate of enzyme activity is shown to be faster at higher temperatures than at lower temperatures.
What happens to enzymes at lower temperatures?
At low temperatures enzymes are never destroyed or stopped working, but because all particles move about far quicker under higher temperatures, they become much less efficient. This is because (in the case of our investigation), at lower temperatures the hydrogen particles were moving about far less than at optimum temperature, so there are less collisions with enzymes, meaning that the hydrogen peroxide molecules are broken down over a far longer period of time. This is why the graph shows that at 5°c, not much digestion occurs, in comparison with optimum temperature. If the experiment was conducted under even lower temperatures, it would take much longer for the enzymes to digest the same amount of food than it would at a higher temperature. If the temperature inside the human body was this low, enzymes would be fairly useless, as their job is to speed up vital chemical reactions.
What happens to enzymes at higher than optimum temperature?
The graph shows that after optimum temperature, the rate of enzyme activity begins to decrease, at a similar rate to its increase before optimum temperature. The reason for this is that above temperatures of somewhere around 45°c, enzymes can become denatured. This does not mean they are destroyed. It means that their shape is permanently altered. When the shape of an enzyme is changed, it stops working completely, because it can no longer use its shape to lock onto molecules in order to break them down. The graph shows a gradual decrease in enzyme activity because they do not all suddenly denature at once. More and more gradually denature as the temperature is raised above optimum temperature. Eventually, no enzymes would be able to digest food anymore. Once an enzyme becomes denatured, it does not matter how fast it’s substrate is moving about, or how often it bumps into it’s substrate it will never be able to digest food molecules.
In summary…
In a summary of the above points: At low temperatures the particles of reacting substances do not have much energy. However, when the substances are at higher temperatures, the particles take in energy. This causes them to move faster and have collisions more often, so the rate of the reaction increases.
The more collisions there are the faster the reaction.
The same is true for chemical reactions inside the human body that are controlled by enzymes, but because enzymes are proteins they will be denatured and no longer work if the temperature exceeds approximately 45°c.
Evaluating
Are My Results Reliable?
When we conducted the experiment everything went relatively well and according to plan. We did everything we could to keep it a fair test and tried to control all the factors that might have made the results inaccurate. However, there were many things that could have caused inaccuracy that were beyond our control.
The key factors in this investigation:
- Temperature
- Time (how long we ran the experiment for)
- Amount of Hydrogen Peroxide
- Size/Surface Area of Liver
These key factors are some of the main things, which affected our results. We tried to keep these constant (if possible) each time we conducted the experiment. The factor that we altered in our investigation was temperature. We also measured Time and Amount of Hydrogen Peroxide.
Do the results look right?
Using science and facts about enzymes that we already knew, it was possible to look at our results table and say if our results looked right or not. I think that our results table looks correct and that the results are quite reliable. The results from my particular group fitted in well with the results of the rest of the class, and also matched what I said in my prediction.
I think the results look right because I already knew (and said in my prediction) that heat speeds up chemical reactions (including biochemical reactions involving enzymes), so I expected the results to show this trend.
Does the graph look right?
The line of best fit that I drew onto the graph displaying my results shows a trend that is easy to spot. It was easy to draw because of the clear layout of the points. It also matches my prediction, and using what I already know about enzymes, I expected the trend that appeared. We conducted the experiment under conditions that were as fair as possible, therefore I think that my graph is accurate enough to be useful and reliable.
Do I have enough evidence to support my conclusion?
In my conclusion I tried to explain the results I obtained. I believe that I do have enough evidence to support my conclusion, but I would have preferred to have much more evidence, because that would have made my conclusion even easier to back up, and the experiment would have been much more worthwhile, as the findings would be far more reliable.
I know I have enough results because it was possible to draw a line of best fit, and guess at how the trend would have continued. However, a good example of how I would have liked more evidence is at the very top of my line of best fit, where I have suggested the optimum temperature for enzyme activity to be. With our current set of results, we can not really be sure where the layout of further points would be around that area, and exactly how the line of best fit should be shaped. For instance, the optimum temperature could have been at a slightly different point, because I was unable to tell exactly when the line of best fit should begin to slope downwards when I drew it.
Using science it is also possible for me to suggest what further results would be without doing further experiments. For example, I know that if the line of best fit was continued below temperatures of 5°c, it would not suddenly stop, it would simply keep decreasing, as enzymes will never be stopped from working at low temperatures, but their activity will be slowed down.
How Well Did We Carry Out The Investigation?
Problems we had that might have affected the results:
Although we did the best we could to control all factors that might have caused our results to be unreliable, there were many things beyond our control that made our experiment less accurate:
Size/Surface area of liver: The small sections of liver available for our experiment could easily have caused inaccuracies throughout the whole experiment. For a start, each group took different pieces of liver, meaning that different amounts of catalyse would be breaking down the hydrogen peroxide in every groups experiment. Also, because the experiment had to be repeated twice, a different piece of liver had to be used each time. Both experiments should have been conducted under exactly the same conditions, but unfortunately we could not be sure of the size and surface area of each section of liver. The surface area of the liver may also have been affected by its position inside the beaker. Less surface area might mean that less catalyse was released.
Amount of hydrogen peroxide: Because the equipment used to measure out liquids and the people doing it were not always accurate the amount of hydrogen peroxide each group used each time they conducted the experiment may have differed, meaning that more had to be broken down and that there was less gas to be displaced in the space between the hydrogen peroxide and the bung.
Expanding gas: When gas is heated it expands. This means that groups conducting the experiment under higher temperatures would have more gas being displaced than groups using lower temperatures, causing the gas syringe to hold gas that was not released by the chemical reaction inside the beaker, meaning that the readings were slightly inaccurate.
Placing the bung into the beaker: When the bung was pushed into the beaker it displaced some gas from the air into the gas syringe. The gas syringe was only supposed to collect gas released from the chemical reaction inside the beaker, so the results that were recorded could have been inaccurate. Also, each groups pushed the bung into the beaker a different way, and at different times. Some tried to displace as little gas as possible, whereas others disregarded this idea. Some groups tried to put the bung in as soon as the liver had been placed inside the beaker, whereas others left a short delay. These differences in the way each group conducting their experiments, led to all of the result being less reliable, and less accurate.
Friction in the gas syringes: Although the gas syringes were fairly accurate items of equipment, friction might have been caused because of previous usage. For example, they might have been damp or contained grit. This could make them fail to properly measure the amount of gas produced.
How fair was our test?
I think that our experiment was very close to being as fair as possible, considering the time and equipment possible, because we considered all the things that might have made the results unreliable, even if we could not control them. We made sure to keep both tests the same by conducting both of them under exactly the same conditions. However, we cannot be sure that other groups tried to make their tests as fair, so although we can be relatively confident about the accuracy of our results, we cannot be sure how reliable the results of other groups were. This means that on the whole the results were not totally reliable if they are looked at all together, unless we can prove that all the experiments were conducted under exactly the same conditions.
What we did to make it a fair test:
Temperature
To keep the temperature fair, we used an accurate thermometer to record the temperature, and wrote down exactly what the temperature was at the start of every experiment.
Time
To keep this fair we used an accurate stopwatch, so we could ensure we knew exactly when to stop the experiment (when to take the bung off the beaker).
Amount of Hydrogen Peroxide
We kept this the same and kept it accurate by using a measuring cylinder to measure out the hydrogen peroxide, instead of the markings on the side of the beaker, because these are only approximate.
Placing the Bung into the Beaker
We kept the same person placing the bung (linking the gas syringe to the beaker) into the top of the beaker containing the hydrogen peroxide. We attempted to place the bung into the beaker at the start of the experiment displacing as little gas as possible each time.
Concentration of Hydrogen Peroxide
Was kept the same by using hydrogen peroxide from the same source each time we carried out the experiment.
How Could We Improve the Investigation?
If we conducted the experiment again, it could be improved in the following ways:
Size of Liver: We could accurately weigh each piece of liver before they were used, and only use pieces between certain weights, e.g. 2.85 g and 4.25 g, so that the irregularity of liver size would be kept to an absolute minimum. Alternatively, we would have to make sure that the sections of liver were cut extremely accurately before using them in our experiment, though this would be difficult to be sure of if we didn’t know exactly where they came from.
We could repeat the experiment a greater number of times: The more times you repeat an experiment, the more sure you can be that your results will be reliable, providing you conduct the experiment as precisely and accurately as possible. If we repeated the experiment more times, we could also calculate the average amount of gas collected, omitting any anomalous results, so that the results could be looked at as a whole.
What Further Work Could I do to Collect Further Evidence?
If I had more time there are other things that I would do to collect extra evidence, that is relevant to this investigation:
Testing at temperatures below and above the lowest and highest temperature we used
I would do this so that I could find out how the trend for cooler temperature continues, and also how much the temperature would have to be increased until there was no enzyme activity whatsoever, i.e. when all the enzymes become denatured.
Carrying out further tests at temperatures around optimum temperature
If I did this, and plotted the results on my graph, I would have a much better idea about how the line of best fit is shaped when it reaches it peak, and exactly where the optimum temperature for enzyme activity is, as it is hard to be sure at the moment, because there are so few points around that area of the graph. I could become sure of what the optimum temperature is for the rate of activity of the enzyme catalyse.
Conducting the experiment for over 20 seconds
We only carried out our experiment for a 20 second period. However, it would be interesting, and also relevant to this investigation, to conduct experiments over other lengths of time. We might be able to find out if enzyme activity increases or decreases the longer they are working for, and if another graph of an experiment using longer (or shorter) periods of time would have a different line of best fit to the one I have already drawn up.