Biochemistry is the branch of chemistry that studies the chemical processes and substances found in living organisms. This chapter explores the structure and function of major biomolecules such as carbohydrates, proteins, lipids, and nucleic acids, as well as the role of enzymes and vitamins in metabolism and health. Students will learn about the classification, sources, and functions of biomolecules, enzyme activity factors, vitamin deficiencies, and the importance of biochemistry in medicine, agriculture, and industry.
1. Which of the following is the main energy source for the body?
- A. Proteins
- B. Carbohydrates ✅
- C. Lipids
- D. Vitamins
Explanation: Carbohydrates are the primary source of energy, broken down into glucose during metabolism.
2. Which is the simplest carbohydrate?
- A. Sucrose
- B. Glucose ✅
- C. Starch
- D. Cellulose
Explanation: Glucose is a monosaccharide, the simplest form of carbohydrate.
3. Proteins are made up of repeating units called:
- A. Fatty acids
- B. Nucleotides
- C. Amino acids ✅
- D. Monosaccharides
Explanation: Proteins are polymers of amino acids linked by peptide bonds.
4. Which of the following is NOT a lipid?
- A. Fats
- B. Oils
- C. Glycogen ✅
- D. Waxes
Explanation: Glycogen is a carbohydrate, not a lipid.
5. The genetic material in cells is made of:
- A. Proteins
- B. Lipids
- C. Nucleic acids ✅
- D. Vitamins
Explanation: DNA and RNA are nucleic acids that store and transmit genetic information.
6. Enzymes act as:
- A. Hormones
- B. Structural molecules
- C. Biological catalysts ✅
- D. Energy storage
Explanation: Enzymes speed up biochemical reactions without being consumed.
7. Which factor does NOT affect enzyme activity?
- A. Temperature
- B. pH
- C. Colour of enzyme ✅
- D. Substrate concentration
Explanation: Enzyme activity depends on temperature, pH, and substrate concentration, not its colour.
8. The enzyme that breaks down starch into maltose is:
- A. Lipase
- B. Amylase ✅
- C. Protease
- D. Catalase
Explanation: Amylase hydrolyzes starch into the disaccharide maltose.
9. Which vitamin is essential for blood clotting?
- A. Vitamin A
- B. Vitamin C
- C. Vitamin K ✅
- D. Vitamin D
Explanation: Vitamin K is necessary for the synthesis of clotting factors in the blood.
10. Vitamin C deficiency causes:
- A. Rickets
- B. Night blindness
- C. Scurvy ✅
- D. Beriberi
Explanation: Scurvy is caused by a lack of vitamin C, affecting collagen synthesis.
11. Which vitamin is produced in the skin when exposed to sunlight?
- A. Vitamin A
- B. Vitamin D ✅
- C. Vitamin E
- D. Vitamin K
Explanation: Sunlight converts cholesterol derivatives in the skin to vitamin D.
12. Which of the following is a disaccharide?
- A. Glucose
- B. Fructose
- C. Sucrose ✅
- D. Galactose
Explanation: Sucrose is made of glucose and fructose linked together.
13. Which lipid serves as an important component of cell membranes?
- A. Triglycerides
- B. Phospholipids ✅
- C. Steroids
- D. Waxes
Explanation: Phospholipids form the bilayer structure of cell membranes.
14. Which nitrogenous base is found only in RNA?
- A. Adenine
- B. Uracil ✅
- C. Thymine
- D. Cytosine
Explanation: Uracil replaces thymine in RNA.
15. Which of the following is a water-soluble vitamin?
- A. Vitamin A
- B. Vitamin D
- C. Vitamin B-complex ✅
- D. Vitamin E
Explanation: Vitamin B-complex and vitamin C are water-soluble vitamins.
16. Which biomolecule stores genetic information?
- A. Proteins
- B. Lipids
- C. DNA ✅
- D. Carbohydrates
Explanation: DNA contains the instructions for the development and functioning of living organisms.
17. Excess intake of vitamin A can cause:
- A. Rickets
- B. Toxicity symptoms like headache and nausea ✅
- C. Scurvy
- D. Pellagra
Explanation: Fat-soluble vitamins like vitamin A can accumulate in the body and cause toxicity.
18. Which enzyme breaks down proteins into peptides?
- A. Amylase
- B. Pepsin ✅
- C. Lipase
- D. Catalase
Explanation: Pepsin hydrolyzes proteins into smaller peptides in the stomach.