Once the enzymes in the small intestine have broken down the food only soluble molecules and indigestible food remains. The small intestine is where most absorption takes place and now the rest of the molecules diffuse into the small intestine wall. The rest of the indigestible waste is passed through in the large intestine, water is absorbed, leaving the indigestible material to pass on to the sacrum, where it is stored until it is passed out of the rectum.
Enzymes
Throughout the whole digestive procedure it is clear that the enzymes play the most important role, by breaking down food. Each enzymes knows which molecule it has to break down and when it does it. This is done by making sure different enzymes work in different conditions so that the wrong enzyme cannot start working too soon. Some enzymes are triggered by certain secretions, like when peptic cells secrete pepsinogen which on contact with acid, is converted into the peptidase enzyme pepsin.
Chief cells produces pepsinogen which is inactive unless it would digest the chief cells, the chief cells occur in the basal regions of the gastric glands which are found in the gastric pits in the stomach wall. The chief cells are stimulated and the pepsinogen molecules are released and are activated by HCl
All enzymes are proteins they have different levels of structure.
Primary – A simple chain of amino acids
Secondary – A Specific arrangement of amino acids in different regions of the protein
Tertiary – A three-dimensional arrangement of the atoms within a single polypeptide chain.
Quaternary – The final shape of a functioning enzyme.
When in their specified environment they produce normal activity. When they are in abnormal conditions then their activity is reduced.
Each enzyme arranges itself to form what is known as an active site, this is where most of the action takes place and where the large molecules are broken down. The active site of every enzyme is shaped specifically for one substrate only, this is known as specificity. Then the lock - and – key hypothesis comes into play, because the active site of each type of enzyme is specifically shaped for one substrate only then no other substrate can fit into the enzyme to be broken down. This creates a lock – and – key situation.
Prediction –
My prediction is backed by the Kinetic Theory in that if I apply twice as much heat there will be twice as much particle movement so the particles can move and do their jobs twice as quickly resulting in the reaction being done twice as quickly. It is also backed by Collision Theory in that if I apply twice as much heat there will be twice as many collisions and therefore the rate of reaction will double. This will only be so until the enzyme denatures after its optimum temperature: 40 - 45ºC.
I believe that the enzyme will work quickest at 30ºC – 45ºC, I choose from 30ºC because it is not too high even thought it will not be working as quickly as possible it will still be fairly fast, and at 40ºC this will probably be the quickest time because it is closest to body temperature.
Apparatus –
3 Test Tubes
1 Conical Flask
1 Cylinder
2 Pipits
1 measuring Cylinder
Water Bath
Test Tube Rack
3 Stop Watches
Pepsin Solution
Hydrochloric Acid
Egg White
Goggles
Gloves
Method – Before we started the actual experiment we needed to know what conditions the pepsin would work best in, I predicted that Acid, Egg White and Pepsin would be the best combination because those are the secretions involved in the stomach when pepsin digests protein, we wanted the evidence to be as accurate as possible so we wanted the enzyme to work in similar conditions as it does in the stomach. We used four test tubes and inside each was a different combination of solutions.
The only combination that showed any reaction was Test Tube No. 4. This only proved what I predicted so I was definite that this was correct. Test Tube No. 1 didn’t work because without pepsin the egg white would have been unable to be broken down. In Test Tube No. 2 there was no acid (HCl) And this is what activates the pepsinogen and pepsin works best in acidic conditions. Test Tube No. 3 Didn’t work because there was no Egg White, so there was nothing for the pepsin to react with.
This proved that in the experiment all of the test tubes were to have in them Acid, Egg White and pepsin.
We then collected all of our apparatus and the solutions we were to use.
We used three test tubes and did them at the same time instead of doing one at a time three times, this would be give us more accurate results because all of the test tubes would be under the same conditions for their temperature.
Firstly we used a measuring cylinder and measured 5ml of egg white which was 99% water, and placed the measuring cylinders on a flat surface when we measured it, so that they would be accurate. When we had poured 5ml of egg white into the three test tubes we then placed them in the test tube rack. We made sure all the test tubes we of the same volume so it would be easier to see that they contained the same amount of egg white in them.
Secondly we used gloves and goggles because we were going to be handling acid, we used pipits and put 3 drops of acid into the three test tubes. The acid we used was 99% water. After doing that we then put the test tube rack into the water bath which was already at the temperature we were first going to experiment on. It was 30ºC, when in water bath we waited for 5 minutes exactly so that the acid and egg white had become a similar temperature to the water in the water bath as it would in the stomach.
Thirdly we added 1ml of pepsin using pipits which was also 99% water, which we measured and squirted it directly into the test tube No.1, so none was left down the side, as soon as we did so we started our stopwatch No.1. We did the same with test tube No.2 as one person squirted in the pepsin another pressed stopwatch No. 2 and we did the same for test tube No. 3.
When in the water bath we shock the test tubes occasionally to mimic the stomach actions of it mixing up the food and gastric juices.
We had to wait until the mixture inside the test tubes turned clear, this meant that the pepsin enzyme had digested the protein enzyme, because the protein particles were now too small to be seen.
When the water went fully clear we then stopped the stop watch assigned to the test tube, and formed a table of our results.
We repeated this procedure with the temperatures below.
Results –
Here are the results:
This is the basic way we have collected our information.
We put down the exact times we were given from the stopwatch and did not round the times up or down, because we wanted the exact results. This made it a little more complicated but it made everything precise.
We have the times from test tube 1, 2 and 3 separate and by doing this we can see that there are marginal differences between the times.
Graphs Showing Information
Graph 1
Each Marker has the time of when its finished. There should be a dip in the centre as the temperatures are 30ºC and 40ºC. When it reaches 50ºC the time shoots up, that is due to the enzyme denaturing. 60ºC has not been put on the graph it was N/A because it did not digest the protein at all.
Graph 2
This is a Bar Graph and it in the same way displays thin information. This time I have Displayed the each individual times, instead of the averages. I wanted to show that even with the separate times you will still be able to see that there is a slight dip.
Once again 30ºC and 40ºC take the least time and 20ºC and 30ºC take the most time.
Conclusion –
I feel that my results portrayed my prediction prior to the experiment. The more the heat varied the more unstable the enzymes were when breaking down the egg white (protein). Looking at the graphs there is a definite dip in time taken as the test tubes are under the temperature of 30ºC and 40ºC. This shows that within these temperatures the enzyme worked at its best. The heat of the water allowed the molecules to move quicker during the reaction with the enzyme and protein, therefore the reaction was much quicker, that would also mean that at 50ºC it would be even quicker, but the quicker the molecules get the start to vibrate more, including the molecules of the enzyme, they start to vibrate so much that they are unable to go back into their place thus becoming denatured. This is when the enzyme has been effected by the heat and the active site where the protein locks into is altered and the protein cannot fit into it to be broken down. At 20ºC the molecules are travailing too slow to react quick enough for any effect reacting and 50ºC is too fast for the enzyme to handle. Therefore 40ºC I the fastest because it is closest to body heat.
Evaluation –
In this experiment we tried to take extra precautions to assure accurate results. We tried to make sure that the test tubes had their own stop watch so that they all started as soon as pepsin was put in. We did our experiment in one area and did not move around with the test tubes, this may have interfered with the results. There were many things as I explained in the method we took with precaution. The evidence received especially the results from the test tubes show us that they were not all exact because the stopped at different times. If all our measurements were correct and they were all under the exact same conditions then they should have been the same. This shows me that we were not perfect and there can be improvements. The measurements for the recreations could have slightly inaccurate which could lead to abnormal results. The concentration of the pepsin, acid and egg white could have all been wrong and that means the whole experiment was not perfect. There are many factors that could interferer with the results of this experiment.
I would say the reliability of my work would be good but not perfect. It would be nearly impossible to get the whole process perfect outside of the stomach environment, because the experiment we set up was all synthetic. I would rely on my evidence because where we could have been we were accurate. I believe that the basis of the experiment has been shown and from that I can say that it does support my conclusion, even though It has anomalies these are fairly minor, things like concentration are speculation and even if they varied slightly it may not give us different results.
