Question

Sample A

Reagent Used	Color Recorded
Lugol's (IKI)	Dark Brown/Black
Benedict's	Orange-Red
Biuret's	Violet
Sudan IV	Red Layer

Sample B

Reagent Used	Color Recorded
Lugol's (IKI)	Dark Brown/Black
Benedict's	Yellow-Orange
Biuret's	Violet
Sudan IV	Red Layer

Sample C

Reagent Used	Color Recorded
Lugol's (IKI)	Yellow
Benedict's	Orange-Red
Biuret's	Violet
Sudan IV	Very little color mixed throughout

Sample D

Reagent Used	Color Recorded
Lugol's (IKI)	Dark Brown/Black
Benedict's	Blue
Biuret's	Violet
Sudan IV	Red Layer

Sample E

Reagent Used	Color Recorded
Lugol's (IKI)	Yellow
Benedict's	Blue
Biuret's	Violet
Sudan IV	Red Layer

Sample F

Reagent Used	Color Recorded
Lugol's (IKI)	Dark Brown/Black
Benedict's	Blue
Biuret's	Violet
Sudan IV	Red Layer

1. a)What were the indicators used for each of the tests for macromolecules? (sugar, protein, fat, starch) B)Give an example of an item in your home lab that you could use to create a positive test for each of the macromolecules (sugar, protein, fat, starch). Assume that you have access to the indicators needed.C)What would you use to make a negative control for these tests? D)Why is it necessary to develop positive and negative controls for each test? E)List the solutions (A through F) and the macromolecules that were detected in each.F)What could be done to increase the sugar content of Sample B?

Answer 1

a.

Lugol's (IKI)

Used for the detection of polysaccharides. If the solution turns dark Brown/Black then polysaccharides are present. If remains as yellow then no polysaccharides (starch) are present.

Benedict's

It is a complex mixture of sodium carbonate, sodium citrate and copper(II) sulfate pentahydrate. It is used to detect reducing sugar. Blue color indicates no reducing sugar is present. Green color indicates traces of the reducing sugar is present. Orange color indicates moderate reducing sugar is present. Red color indicates a high amount of reducing sugar is present.

Biuret's

Used to know the presence of proteins. If proteins are present then solution color turns to violet.

Sudan IV

Binds with the hydrocarbon chain of the lipids. It gives red coloration if lipids are present.

b.

Lugol's (IKI) reagent can be used to know the presence of starch. The corn contains starch.

Benedict's reagent can be used for the presence of reducing sugar. Table sugar is a reducing sugar

Biuret's reagent can be used to detect the proteins. Meat is a good source of protein.

Sudan IV reagent can be used to detect lipids. Oil is a good source of lipids.

c.

In the negative control, no change in the color of any reagent is expected.

Lugol's (IKI) reagent can be used in the absence of starch.

Benedict's reagent can be used in the absence of reducing sugar.

Biuret's reagent can be used in the absence of proteins.

Sudan IV reagent can be used in the absence of lipids.

d.

Positive control will tell you your reagent is working properly. That means reagent solutions are functional.

The negative control is mainly used to know the false-positive result. In the negative control, we do not add macromolecules. Suppose the tubes which you are using for the test are not washed properly and remains of macromolecules are still there. Then, this will give you a positive result which will be read as false positive. Therefore, in order to avoid it, negative controls are important.

e. Already explained above in a.

f. You need to add more sugar to the test solution.