50 MCQ on Biology for NEET and CSIR EXAM Part - 3

1. The enzyme responsible for joining Okazaki fragments during DNA replication is:
   A. DNA polymerase I
   B. DNA ligase
   C. Helicase
   D. Primase
   Answer: B

2. Which photosystem is primarily responsible for photolysis of water?
   A. Photosystem I
   B. Photosystem II
   C. Cytochrome complex
   D. ATP synthase
   Answer: B

3. In the Calvin cycle, the first stable product is:
   A. Ribulose bisphosphate
   B. Phosphoglyceraldehyde
   C. 3-phosphoglycerate
   D. Oxaloacetate
   Answer: C

4. Which enzyme converts fructose-6-phosphate to fructose-1,6-bisphosphate in glycolysis?
   A. Hexokinase
   B. Phosphofructokinase
   C. Aldolase
   D. Pyruvate kinase
   Answer: B

5. The Bohr effect refers to:
   A. Oxygen binding to hemoglobin
   B. Effect of CO₂ and pH on hemoglobin affinity for oxygen
   C. Oxygen transport by plasma
   D. Oxygen storage in muscles
   Answer: B

6. Which immunoglobulin is the most abundant in human blood?
   A. IgA
   B. IgM
   C. IgG
   D. IgE
   Answer: C

7. Which enzyme catalyzes conversion of RNA primer to DNA during replication?
   A. DNA polymerase I
   B. DNA polymerase III
   C. Ligase
   D. Primase
   Answer: A

8. The lac operon is activated when:
   A. Lactose is absent
   B. Glucose is high
   C. Lactose binds to repressor
   D. Repressor binds operator
   Answer: C

9. The TCA cycle generates how many NADH molecules per glucose molecule?
   A. 4
   B. 6
   C. 8
   D. 10
   Answer: B

10. Which part of nephron is impermeable to water?
    A. Proximal tubule
    B. Descending limb
    C. Ascending limb of Henle
    D. Collecting duct
    Answer: C

11. In C4 plants, CO₂ fixation occurs initially in:
    A. Bundle sheath cells
    B. Mesophyll cells
    C. Guard cells
    D. Epidermal cells
    Answer: B

12. The enzyme RuBisCO acts as:
    A. Only carboxylase
    B. Only oxygenase
    C. Both carboxylase and oxygenase
    D. Hydrolase
    Answer: C

13. The hormone responsible for apical dominance is:
    A. Auxin
    B. Cytokinin
    C. Ethylene
    D. ABA
    Answer: A

14. The myelin sheath around neurons is produced by:
    A. Schwann cells
    B. Astrocytes
    C. Microglia
    D. Neurons
    Answer: A

15. Which vitamin deficiency causes pernicious anemia?
    A. Vitamin B1
    B. Vitamin B6
    C. Vitamin B12
    D. Vitamin C
    Answer: C

16. Which hormone regulates circadian rhythm?
    A. Thyroxine
    B. Melatonin
    C. Insulin
    D. Cortisol
    Answer: B

17. The process of programmed cell death is called:
    A. Necrosis
    B. Apoptosis
    C. Autolysis
    D. Lysis
    Answer: B

18. The enzyme nitrogenase is found in:
    A. Rhizobium
    B. Nitrosomonas
    C. Nitrobacter
    D. Pseudomonas
    Answer: A

19. Which plant hormone inhibits growth and induces dormancy?
    A. Auxin
    B. Cytokinin
    C. Abscisic acid
    D. Gibberellin
    Answer: C

20. Which blood vessel has the highest blood pressure?
    A. Vein
    B. Artery
    C. Capillary
    D. Venule
    Answer: B

21. Which stage of meiosis resembles mitosis?
    A. Meiosis I
    B. Meiosis II
    C. Prophase I
    D. Metaphase I
    Answer: B

22. The electron transport chain in mitochondria occurs in:
    A. Matrix
    B. Outer membrane
    C. Inner membrane
    D. Intermembrane space
    Answer: C

23. Which enzyme converts pyruvate to acetyl-CoA?
    A. Pyruvate carboxylase
    B. Pyruvate dehydrogenase
    C. Lactate dehydrogenase
    D. Isomerase
    Answer: B

24. The hormone responsible for uterine contraction during childbirth is:
    A. Oxytocin
    B. Estrogen
    C. Progesterone
    D. Prolactin
    Answer: A

25. Which structure forms the filtration barrier in kidney?
    A. Bowman's capsule
    B. Glomerular membrane
    C. Loop of Henle
    D. Distal tubule
    Answer: B

26. Which enzyme synthesizes RNA from DNA template?
    A. DNA polymerase
    B. RNA polymerase
    C. Ligase
    D. Primase
    Answer: B

27. The genetic code is read in:
    A. Overlapping manner
    B. Continuous triplets
    C. Doublets
    D. Random sequence
    Answer: B

28. The energy stored in ATP is in:
    A. Glycosidic bonds
    B. Hydrogen bonds
    C. Phosphoanhydride bonds
    D. Peptide bonds
    Answer: C

29. The largest lymphatic organ in the human body is:
    A. Thymus
    B. Spleen
    C. Lymph node
    D. Tonsil
    Answer: B

30. Which blood protein transports iron?
    A. Hemoglobin
    B. Transferrin
    C. Albumin
    D. Globulin
    Answer: B

31. The respiratory center is located in:
    A. Cerebellum
    B. Medulla oblongata
    C. Hypothalamus
    D. Cerebrum
    Answer: B

32. Which organelle detoxifies drugs in liver cells?
    A. Rough ER
    B. Smooth ER
    C. Golgi body
    D. Lysosome
    Answer: B

33. The enzyme that synthesizes ATP in mitochondria is:
    A. ATP synthase
    B. Cytochrome oxidase
    C. NADH dehydrogenase
    D. Succinate dehydrogenase
    Answer: A

34. Which ecological interaction benefits both species?
    A. Parasitism
    B. Commensalism
    C. Mutualism
    D. Predation
    Answer: C

35. The symbiotic nitrogen fixation in legumes occurs in:
    A. Stem
    B. Leaves
    C. Root nodules
    D. Flowers
    Answer: C

36. Which enzyme converts angiotensin I to angiotensin II?
    A. Renin
    B. ACE
    C. Pepsin
    D. Amylase
    Answer: B

37. Which type of immunity is obtained from vaccines?
    A. Passive immunity
    B. Natural immunity
    C. Artificial active immunity
    D. Innate immunity
    Answer: C

38. The universal genetic code was experimentally confirmed by:
    A. Watson and Crick
    B. Nirenberg and Khorana
    C. Mendel
    D. Darwin
    Answer: B

39. Which cell organelle contains its own DNA and ribosomes?
    A. Lysosome
    B. Golgi body
    C. Mitochondria
    D. Peroxisome
    Answer: C

40. The main photosynthetic pigment in plants is:
    A. Chlorophyll a
    B. Chlorophyll b
    C. Carotene
    D. Xanthophyll
    Answer: A

41. Which structure forms synaptic connection between neurons?
    A. Axon terminal
    B. Dendrite
    C. Myelin sheath
    D. Soma
    Answer: A

42. Which process converts glucose into glycogen?
    A. Glycolysis
    B. Glycogenesis
    C. Glycogenolysis
    D. Gluconeogenesis
    Answer: B

43. Which hormone increases calcium levels in blood?
    A. Calcitonin
    B. Parathyroid hormone
    C. Insulin
    D. Glucagon
    Answer: B

44. The enzyme pepsin digests:
    A. Carbohydrates
    B. Proteins
    C. Lipids
    D. Nucleic acids
    Answer: B

45. Which part of eye contains photoreceptor cells?
    A. Retina
    B. Cornea
    C. Iris
    D. Lens
    Answer: A

46. Which cycle is responsible for carbon fixation in plants?
    A. Krebs cycle
    B. Calvin cycle
    C. Glycolysis
    D. Urea cycle
    Answer: B

47. Which molecule donates electrons to Photosystem I?
    A. NADPH
    B. Plastocyanin
    C. Ferredoxin
    D. Water
    Answer: B

48. The enzyme catalase breaks down:
    A. Hydrogen peroxide
    B. Carbon dioxide
    C. Ammonia
    D. Nitrite
    Answer: A

49. Which hormone stimulates milk production in mammals?
    A. Prolactin
    B. Oxytocin
    C. Estrogen
    D. Progesterone
    Answer: A

50. Which ecological level includes both living and non-living components?
    A. Population
    B. Community
    C. Ecosystem
    D. Species
    Answer: C

---