Question 1

Which of the following best explains why lipids such as fats and oils do not dissolve in water?

Accepted Answer

Lipids have a low degree of polarity and are consequently insoluble in water.

Question 2

During the Benedict’s test, which structural feature of sugars allows them to act as reducing agents?

Accepted Answer

Presence of a free aldehyde or ketone group ($-CHO$ or $>C=O$) that can donate electrons.

Question 3

A student performs the IKI test on a solution and observes a blue-black color. What does this indicate about the sample?

Accepted Answer

The sample contains starch or a similar polysaccharide.

Question 4

Which of the following is a correct structural formula for a disaccharide formed from two glucose molecules?

Accepted Answer

$C_{12}H_{22}O_{11}$

Question 5

Why does the Sudan Black test result in a phase separation when testing vegetable oil?

Accepted Answer

Sudan Black partitions into the lipid phase due to its non-polar nature, causing a visible separation.

Question 6

Which of the following best describes the difference between a fat and a fatty acid?

Accepted Answer

A fat is a triglyceride formed from three fatty acids and glycerol, while a fatty acid is a single carboxylic acid with a long hydrocarbon chain.

Question 7

In the Biuret test for proteins, what is the chemical basis for the color change observed?

Accepted Answer

Copper ions ($Cu^{2+}$) form a complex with the peptide bonds in proteins, producing a violet color.

Question 8

A solution tests positive in the Ninhydrin test but negative in the Biuret test. What does this most likely indicate about the sample?

Accepted Answer

The sample contains free amino acids but not polypeptides.

Question 9

Which of the following is the correct general formula for a monosaccharide?

Accepted Answer

$C_nH_{2n}O_n$ where $n = 3$ to $7$

Question 10

Which of the following statements about proteins is TRUE?

Accepted Answer

Proteins are polymers of amino acids linked by peptide bonds.

Question 11

A student adds Benedict’s reagent to a solution containing maltose and heats it. What color change should the student expect if maltose is present?

Accepted Answer

The solution turns green, yellow, orange, or red depending on the concentration of reducing sugars.

Question 12

Which of the following best explains why starch gives a positive result in the IKI test?

Accepted Answer

IKI forms a complex with the helical structure of polysaccharides like starch, producing a blue-black color.

Question 13

Which of the following is a correct description of a triglyceride?

Accepted Answer

A molecule composed of three fatty acids and one glycerol.

Question 14

Which of the following tests would you use to detect the presence of proteins in a solution?

Accepted Answer

Biuret test

Question 15

A sample contains both starch and glucose. Which combination of tests would best confirm the presence of both substances?

Accepted Answer

IKI test and Benedict’s test

Question 16

Which of the following is a correct representation of the peptide bond formed between two amino acids?

Accepted Answer

$-CO-NH-$

Question 17

A student tests a solution with Ninhydrin reagent and observes a purple color. What does this indicate?

Accepted Answer

The presence of free amino groups (amino acids).

Question 18

Which of the following best describes the difference between a monosaccharide and a polysaccharide?

Accepted Answer

Monosaccharides are simple sugars with a single unit, while polysaccharides are complex carbohydrates composed of many monosaccharide units linked together.

Question 19

Which of the following statements about the Biuret test is correct?

Accepted Answer

A positive Biuret test indicates the presence of peptide bonds in proteins or polypeptides.

Biological Macromolecules: Identification and Properties

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