Question

Question 13 Find out a qualitative test for proteins, fats and oils, amino acids and test any fruit juice, saliva, sweat and urine for them.

Class XI Biology Chapter - Biomolecules Page 161

Answer 1

) Test for protein
Biuret’s test – If Biuret’s reagent is added to protein, then the colour of the reagent changes from light blue to purple.


(b) Test for fats and oils
Grease or solubility test
(c) Test for amino acid
Ninhydrin test – If Ninhydrin reagent is added to the solution, then the colourless solution changes to pink, blue, or purple, depending on the amino acid.
Item
Name of the test
Procedure
Result
Inference
1.
Fruit juice
Biuret’s test
Fruit juice + Biuret’s reagent
Colour changes from light blue to purple
Protein is present.


Grease test
To a brown paper, add a few drops of fruit juice.
No translucent spot
Fats and oils are absent or are in negligible amounts.


Ninhydrin test
Fruit juice + Ninhydrin reagent + boil for 5 minutes
Colourless solution changes to pink, blue, or purple colour
Amino acids are present.
2.
Saliva
Biuret’s test
Saliva + Biuret’s reagent
Colour changes from light blue to purple
Proteins are present.


Grease test
On a brown paper, add a drop of saliva.
No translucent spot
Fats/oils are absent.


Ninhydrin test
Saliva + Ninhydrin reagent + boil for 5 minutes
Colourless solution changes to pink, blue, or purple colour
Amino acids are present.
3.
Sweat
Biuret’s test
Sweat + Biuret’s reagent
No colour change
Proteins are absent.


Solubility test
Sweat + Water
Oily appearance
Fats/oil may be present.


Ninhydrin test
Sweat + Ninhydrin reagent + boil for 5 minutes
No colour change, solution remains colourless
Amino acids are absent.
4.
Urine
Biuret’s test
Few drops of urine + Biuret’s reagent
Colour changes from light blue to purple
Proteins are present.


Solubility test
Few drops of urine + Water
Little bit of oily appearance
Fats may or may not be present.


Ninhydrin test
Few drops of urine + Ninhydrin reagent + boil for 5 minutes
Colourless solution changes to pink, blue, or purple colour depending on the type of amino acid

Answer 2

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