Danii7
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1. Why does the procedure for testing for proteins include making observations with the Biuret as a layer on top of the sample before mixing?

2. An effective qualitative test must give a clear positive result whenever the substance being tested for is present. This means it avoids ‘false negatives’. It must also not give a positive result due to the presence of some other substance (this would be a false positive). Explain, in terms of their solubility in different solvents and your knowledge of the emulsion test, why you do not see false positives due to:
- Monosaccharides and disaccharides
- Starch
- Nucleic acid
- Protein

3. The emulsion test is qualitative. How could it be made the basis for a semi-quantitative test (giving an indication of whether lipids are present at high, medium or low concentration) or even a fully quantitative test for lipids?
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Starlight2000
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(Original post by Danii7)
1. Why does the procedure for testing for proteins include making observations with the Biuret as a layer on top of the sample before mixing?

2. An effective qualitative test must give a clear positive result whenever the substance being tested for is present. This means it avoids ‘false negatives’. It must also not give a positive result due to the presence of some other substance (this would be a false positive). Explain, in terms of their solubility in different solvents and your knowledge of the emulsion test, why you do not see false positives due to:
- Monosaccharides and disaccharides
- Starch
- Nucleic acid
- Protein

3. The emulsion test is qualitative. How could it be made the basis for a semi-quantitative test (giving an indication of whether lipids are present at high, medium or low concentration) or even a fully quantitative test for lipids?
Can someone help me with this!!!
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typicalvirgo
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1. So that any colour change can be considered. The colour for a positive result is similar to the normal colour. (I think)

2.Monosaccharides and disaccharides are not soluble in alcohol. Starch, nucleic acids and proteins are insoluble in alcohol. In order for the emulsion test to work, the sample must be soluble in alcohol, like lipids. Water is then added and the solution shaken, resulting in a white emulsion layer above the water.

3.Test various concs of lipids and place an equal volume of each emulsion solution into a colorimeter, testing it against absorbtion and transmission.
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Mue
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1) incase the solution you are testing is not clear, like if you are testing liver or something
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Vyjayanthi
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Can anyone help with the paper and answer keys for the PAG 9.2 Biology Qualitative testing of lipids?
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