Digestion is the breaking down of large, insoluble food molecules into small, soluble molecules. (This is done so that food can move from the alimentary canal into the blood.) There are two types of digestion, namely mechanical and chemical . Mechanical digestion is where The food must first be broken down into smaller bits The teeth are used for mechanical digestion. Food is cut by the incisors and crushed between the molars. The stomach churns the food as the muscles contract. The small intestine mixes the food by a process of segmentation and peristalsis. Chemical digestion This is the breaking down of large, complex, insoluble molecules into smaller, simple, soluble molecules. Enzymes that break up the complex molecules do the breaking down. The enzyme trypsin, which we use in this experiment is used in digestion. It works in the duodenum and helps with the final stages of digestion. The enzyme is produced in the pancreas as part of the pancreatic juices, many other enzymes are produced also such as lipase’s and amylase’s. These enzymes are released into the duodenium to help digest the food types respectively. As I have already said I predict the enzyme to work best in slightly alkaline conditions, I have come to this theory as the pancreatic juices contain a solution called sodium hydrogen carbonate (NaHCO3) this solution is produced to neutralise the stomach acids as the duodenum has no or very little alkaline mucus lining therefore the conditions in the duodenum will be slightly acidic, this theory is backed up more by the fact that the liver releases a substance called Bile which actually contains more sodium hydrogen carbonate to neutralise the stomach acids knowing this I predict the optimum temperature for the enzyme to function will be pH8 as this is a weak alkali and will work well in the alkali conditions of the duodenum.
Apparatus
- Electronic water bath
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10 ml3 Syringes
- 40 splints
- A pair of scissors
- 2% pancreatic solution (containing trypsin)
- pH buffers 6-10
- 5 test tubes
- Test tube rack
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5 ml3 syringes
- White tile
- Scalpel
- Film negatives from same roll of film
- Stop clock
- Sticky labels
Plan
- I will collect five test tubes
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I will fill each test tube with 4 ml3 of the pancreatin using a 5ml3 syringe
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I will then add 4 ml3 the pH buffer to each test tube, using a different syringe to the one I used when adding pancreatin, ranging from pH 6-10.
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I will then leave the test tubes in the electronic water bath to acclimatise for thirty minutes, the temperature of the water bath will be at 50°C as it was found out in the preliminary work that this was the optimum temperature for the pancreatin
- I shall then cut the negatives to 8mm wide, I shall do this five times, and make sure they are exact
- I shall then make a small slit in each of the splints and place a negative cutting in each
- I will then label the splints ranging from pH 6-10 so that the pH of the solution is clear to me
- I shall then place each splint in a test tube and start the stop clock
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I will check the negative after three minutes and then every thirty seconds after that, until I can see that the negative is about to go, then I shall check more frequently ∴being as accurate as possible
- I shall check my negative against a white tile so a clear end point is visible
- After all the negatives go colourless i shall record my results in a table.
- I shall then plot a graph of my results
- I shall then repeat the above steps using intermediate values: 7.5 and 8.5 and record the results in a table as before
- I shall then take this further using intermediate values: 7.5,7.75,8.25 and 8.5 and record my results in a table
- The control shall then be carried out and this will show that just using pH buffers cannot break down the gelatine. The control is going to be an experiment in which I just put the film negatives into a solution of pH buffer.
Results
Fair test
Method
- I changed the width that the photographic film was cut to, I changed it to 1cm as 8mm was too hard to measure and ensure accuracy, 1 cm being easier to measure and cut therefore resulting in better accuracy and an all round fairer experiment.
- I decided to change the time intervals in which I checked the photographic film as I found after three minutes, some of my tests were almost at the end point, so I checked after two minutes and those of which had almost gone I checked more frequently to ensure I got the end point exact
Graph
Analysis
I can conclude from my first set of results that, as predicted in my hypothesis, pH8 was in fact the pH that digested the gelatine in the fastest time. When I took my experiment further and investigated intermediate values I found that pH8 was still the optimum working PH for the enzyme, so I decided to try intermediate intermediate values and the results actually came quite pleasing, I was able to deduct from my results that pH 8.25 was actually the optimum working temperature, I found this useful as it gave me a much more accurate idea of the conditions in the duodenum.
As I mentioned in my hypothesis the conditions in the duodenum are slightly alkaline due to the sodium hydrogen carbonate released there. We can see from the results that there is a very significant gap between the time taken for pH7 and pH6 to digest the gelatine pH 6 was taking in excess of 1000 seconds whereas pH7 was taking around 800 this can be reflected on the fact that the conditions in the duodenum are alkaline therefore as mentioned in my hypothesis the enzyme would become denatured in acidic conditions.
Trypsin as mentioned in my hypothesis is an enzyme ewhich breaks down large insoluble food molecules into smaller ones easier to digest. The specialised environment in which the trypsin works is within the duodenum which is at the beginning of the small intestine. The conditions in the duodenum, as I predicted are the optimum working pH for trypsin I think this because the enzyme needs to work within those conditions naturally.
My results backed up the fact that in my hypothesis I stated that the enzyme trypsin would break down the gelatine holding the silver and black pigment to the clear plastic strip, we could see a clear end point as the negative was completely transparent when held up against a white tile showing the enzyme had digested the gelatine adhesive.
Evaluation
I think that on the whole the experiment went well, my results were good and consistent although there are a few things I would change errors seemed to be in the minority.
If I were to conduct this experiment again I would change the following things:
- I would make the end point much clearer as I may have lost a few seconds trying to decide if the film was fully clear or not
- During the experiment we had very little time to carry out the practical, we took a series of lessons to complete our results this resulted in having to use different apparatus maybe not keeping the experiment a fair test, if I could do this again I would carry out the experiment over a series of three lessons back to back in order to keep the apparatus the same.
- As we had so little time I had to run trials simultaneously which made it much harder for me to check for end points, if I were to carry out this experiment again I would run each trial individually so that I could distinguish the end point precisely of each film negative.
- The enzyme/buffer mix that we used to digest the gelatine of the photographic negative had to be used over and over again, due to time and apparatus constraints, Having to re-use this solution may have caused the enzyme to act slower in the later trails. If I were to carry out this experiment again I would use fresh buffer/enzyme for every trail.
- In my plan I also stated that I would leave the enzyme for thirty minutes to acclimatise but when it came down to it I did not have enough time and they were only left for 15 minutes. This ment that it became unfair as the enzymes became more acclimatised to the temperature as seen the my later intermediate results.
- Another factor affecting the fairness of my results was that the pHs might not have been exactly as stated on the beaker as there are so many of us in the group the syringes could have gotten muddled resulting in the buffer becoming contaminated.
- I made up the intermediate values myself using the pH buffers at a 50:50 ratio as best as I could, although the values could have been slightly out, if I were to carry out this experiment again I would have used a pH probe to check the pH of the solution.
In my experiment I could find no values that suggested to be anomalous, this shows that although I had errors in my experiment the results came out consistent and accurate. I would rate my experiment as a success.
By Tom Kirkham
