Biological molecules

Question 1

What elements make up carbohydrates?

Answer 1

Carbohydrates are made up of carbon, hydrogen, and oxygen.

Question 2

What are carbohydrates made of?

Answer 2

Long chains of simple sugars, such as glucose.

Question 3

What is glucose?

Answer 3

Glucose is a simple sugar, also called a monosaccharide.

Question 4

What are polysaccharides and give examples.

Answer 4

Polysaccharides are long chains of glucose. Examples include starch, glycogen, and cellulose.

Question 5

What elements are found in all proteins?

Answer 5

Carbon, hydrogen, oxygen, and nitrogen. Some also contain sulfur.

Question 6

What are proteins made of?

Answer 6

Long chains of amino acids.

Question 7

How many different amino acids are there?

Answer 7

There are 20 different amino acids.

Question 8

What makes each amino acid different?

Answer 8

All amino acids have the same basic structure, but the R group is different in each one.

Question 9

Why are there so many different proteins?

Answer 9

Amino acids can be arranged in many different sequences, creating a variety of proteins.

Question 10

What elements are found in fats (lipids)?

Answer 10

Carbon, hydrogen, and oxygen.

Question 11

What is the basic unit of most fats in the body?

Answer 11

One glycerol molecule bonded to three fatty acid chains (triglyceride).

Question 12

What is a triglyceride?

Answer 12

A lipid made of one glycerol molecule and three fatty acid chains.

Question 13

What are the two types of lipids?

Answer 13

Fats (solid at room temperature) and oils (liquid at room temperature).

Question 14

What does DNA stand for?

Answer 14

Deoxyribonucleic acid.

Question 15

What is the function of DNA in an organism?

Answer 15

DNA contains the instructions for growth and development.

Question 16

What is the structure of DNA?

Answer 16

Two strands twisted into a double helix.

Question 17

What are the building blocks of DNA?

Answer 17

Nucleotides

Question 18

What are the four DNA bases?

Answer 18

Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).

Question 19

Which DNA bases pair together?

Answer 19

Adenine with Thymine (A–T), Cytosine with Guanine (C–G).

Question 20

What does the iodine solution test detect?

Answer 20

The presence of starch.

Question 21

What color is iodine solution before the test?

Answer 21

Orange to brown.

Question 22

What is a positive result for the iodine test?

Answer 22

Color change from orange-brown to blue-black.

Question 23

What does a negative iodine test indicate?

Answer 23

No color change; starch is not present.

Question 24

How do you perform the iodine test for starch?

Answer 24

Add a few drops of iodine solution to the food sample. If starch is present, the solution changes from orange-brown to blue-black.

Question 25

Why does the iodine solution turn blue-black in the presence of starch?

Answer 25

Because starch reacts with iodine to form a starch-iodine complex, which is blue-black in color.

Question 26

What does a blue-black color change in an iodine test indicate?

Answer 26

It confirms the presence of starch in the tested sample.

Question 27

What will the iodine test look like if no starch is present?

Answer 27

The solution stays orange-brown — no color change.

Question 28

How do you perform the Benedict’s test for reducing sugars?

Answer 28

Add Benedict’s solution to the food sample and heat it in a water bath for 2–3 minutes. A positive result is a color change from blue to green, yellow, orange, or brick-red.

Question 29

What does a color change from blue to brick-red in the Benedict’s test indicate?

Answer 29

It indicates the presence of reducing sugars such as glucose or maltose.

Question 30

Why is heating required in Benedict’s test?

Answer 30

Heating helps the reducing sugars react with copper(II) ions in Benedict’s solution, causing the color change.

Question 31

What does it mean if the Benedict’s solution stays blue after heating?

Answer 31

No reducing sugars are present in the sample.

Question 32

What is the ideal temperature range for heating during the Benedict’s test for reducing sugars?

Answer 32

The Benedict’s solution should be heated to around 80°C to 100°C in a water bath. This helps the reaction occur between reducing sugars and the solution, causing a color change if sugars are present.

Question 33

How do you perform the Biuret test for proteins?

Answer 33

Add a few drops of Biuret solution (or mix sodium hydroxide and copper sulfate) to the food sample. A positive result is a color change from blue to purple/lilac.

Question 34

What color change indicates the presence of protein in the Biuret test?

Answer 34

The solution turns from blue to purple/lilac if protein is present.

Question 35

What causes the color change in the Biuret test?

Answer 35

The copper ions in the Biuret solution react with peptide bonds in proteins, forming a purple complex.

Question 36

What does it mean if there’s no color change in the Biuret test?

Answer 36

No protein is present in the tested sample.

Question 37

How do you test for fats and oils using the ethanol emulsion test?

Answer 37

Mix the food sample with about 2 cm³ of pure ethanol and shake well. Add an equal volume of cold distilled water. A positive result is a cloudy white emulsion, indicating the presence of fats or oils. Ethanol is clear and colorless at the start.

Question 37

How do you perform the DCP-IP test for Vitamin C?

Answer 37

Add 1 cm³ of DCP-IP solution (blue at start) to a test tube. Add a small amount of the food sample solution. Positive test: The blue color of the DCP-IP dye disappears. Negative test: The blue color remains unchanged.

Question 37

What is tested using the DCP-IP test?

Answer 37

Vitamin C.

Question 37

What is tested using the ethanol emulsion test?

Answer 37

Fats and oils.

Question 37

What is the positive result for the ethanol emulsion test?

Answer 37

A cloudy emulsion forms.

Question 38

What is the positive result for the DCP-IP test?

Answer 38

Blue dye disappears.