An experiment to investigate the action of saliva on starch:

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Introduction

An experiment to investigate the action of saliva on starch: Research question Do enzymes in our saliva break up starch into simple sugars (mono- or disaccharides)? Introduction Enzymes are globular proteins, which act as biological catalysts. They speed up reactions by binding to a substrate, such as for example the enzyme amylase, which binds to starch (a polysaccharide) in order to break it down into di- and monosaccharides. They are present in all organisms in thousand of different forms, most enzymes specific to only one substrate. An enzyme has an active site, at which it binds to a substrate, which is specific to its shape. An example for this is the enzyme amylase which catalyses the breakdown of starch, a polysaccharide for example found in potatoes. When it is digested by amylase, it will be broken down into disaccharides, which are sugars such as maltose. Then another enzyme, maltase, will break the disaccharide down into glucose, which is the monomer starch is made of. Starch is a carbohydrate consisting of a large number of glucose units joined together. It is produced by all green plants as an energy store.

Middle

Draw in a little air and quickly and thoroughly mix the contents of the syringe by inverting it two or three times. 7) Hold the syringe vertically and immediately squeeze the plunger carefully to expel one drop of the mixture into the first drop of iodine solution on the tile. Do not let the tip of the syringe touch the iodine solution. Note the time. 8) Continue to test single drops of the mixture at intervals of 30 seconds until the iodine solution shows no further change in colour. 9) Now expel 1cm3 of the remaining mixture in the syringe into a test-tube. Test this for the presence if reducing sugars using Benedict's solution. Put it into a water bath and leave it for 10 minutes. Then take it out. 10) Ten expel another 1cm3 of the remaining mixture in the syringe into a test-tube. Test this for the presence of reducing sugars, using Benedict's solution. Put it into a water bath and leave it for 10 minutes. Then take it out again.

Conclusion

* 3) What conclusion can you draw from the results of the tests in steps 9 and 10? - The solution turns brick red. That means that the starch in the solution has been broken down to reducing sugars by the amylase in the saliva. * 4) What test should you perform on the original starch suspension before you can be confident of your answer to question 3? -Iodine test to see if starch has completely been broken down. If it turns black blue, starch is still present! * 5) How are the properties of saliva affected by boiling? - The enzyme amylase in saliva is denatured and so the starch in the saliva stays unchanged * 6) Saliva normally acts on starch at body temperature (37°C). If you had carried out the whole experiment at this temperature, what difference would you expect this to have made to the results you obtained? -The results would have been much faster. The colour would change much faster for example from blue/black directly to navy blue or dark purple instead of changing much slower. (as shown in the result table) The experiment would be much faster to do and to finish. Biology-SDH by Rebecca Kriegbaum

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