1. Which of the following enzymes is responsible for unwinding the DNA double helix during replication?

  • A. DNA ligase
  • B. DNA helicase
  • C. DNA polymerase I
  • D. Primase

Answer: B. DNA helicase

Explanation: DNA helicase breaks hydrogen bonds between complementary bases, unwinding the DNA double helix during replication.

2. Which blood vessel carries oxygenated blood from the lungs to the heart?

  • A. Pulmonary artery
  • B. Aorta
  • C. Pulmonary vein
  • D. Superior vena cava

Answer: C. Pulmonary vein

Explanation: Pulmonary veins are the only veins that normally carry oxygenated blood, transporting it from the lungs to the left atrium.

3. Which hormone is secreted by the β-cells of the Islets of Langerhans?

  • A. Glucagon
  • B. Insulin
  • C. Somatostatin
  • D. Adrenaline

Answer: B. Insulin

Explanation: β-cells of the pancreas secrete insulin, which lowers blood glucose levels by promoting glucose uptake.

4. Which nitrogenous base is present in RNA but absent in DNA?

  • A. Adenine
  • B. Cytosine
  • C. Uracil
  • D. Guanine

Answer: C. Uracil

Explanation: RNA contains uracil in place of thymine, which is found in DNA.

5. Which part of the nephron is primarily responsible for the selective reabsorption of glucose and amino acids?

  • A. Bowman's capsule
  • B. Proximal convoluted tubule
  • C. Loop of Henle
  • D. Distal convoluted tubule

Answer: B. Proximal convoluted tubule

Explanation: The proximal convoluted tubule reabsorbs nearly all glucose, amino acids, and a large proportion of water and ions.

6. Which of the following is a connecting link between reptiles and birds?

  • A. Peripatus
  • B. Archaeopteryx
  • C. Balanoglossus
  • D. Lungfish

Answer: B. Archaeopteryx

Explanation: Archaeopteryx possessed reptilian features such as teeth and a long tail along with avian feathers and wings.

7. Which scientist proposed the "One Gene-One Enzyme" hypothesis?

  • A. Watson and Crick
  • B. Beadle and Tatum
  • C. Jacob and Monod
  • D. Avery, MacLeod and McCarty

Answer: B. Beadle and Tatum

Explanation: Beadle and Tatum demonstrated that genes control the synthesis of specific enzymes using Neurospora crassa.

8. Which of the following organisms reproduces by multiple fission?

  • A. Amoeba
  • B. Hydra
  • C. Plasmodium
  • D. Yeast

Answer: C. Plasmodium

Explanation: Plasmodium undergoes multiple fission (schizogony), producing many daughter cells simultaneously.

9. Which vitamin is essential for normal blood clotting?

  • A. Vitamin A
  • B. Vitamin C
  • C. Vitamin D
  • D. Vitamin K

Answer: D. Vitamin K

Explanation: Vitamin K is required for the synthesis of several clotting factors in the liver.

10. Which gas is released during the light reaction of photosynthesis?

  • A. Carbon dioxide
  • B. Nitrogen
  • C. Oxygen
  • D. Hydrogen

Answer: C. Oxygen

Explanation: During photolysis in Photosystem II, water molecules are split, releasing oxygen as a by-product.