Part 2: Skeletal Muscle Structure – Myofibrils, Sarcomere, Proteins
Part 2 (25 MCQs) on Skeletal Muscle Structure – Myofibrils, Sarcomere, Proteins from Chapter 20: Locomotion and Movement.
These are NCERT Class 11 + NEET UG standard.
Part 2: Skeletal Muscle Structure – Myofibrils, Sarcomere, Proteins
Q1. The structural and functional unit of skeletal muscle is:
a) Myofibril
b) Sarcomere
c) Actin filament
d) Myosin filament
Answer: b) Sarcomere
Explanation:
- (a) Myofibril – made up of sarcomeres.
- ✅ (b) Sarcomere – Z line to Z line = unit of contraction.
- (c), (d) – components only.
Q2. Skeletal muscles are also called:
a) Smooth muscles
b) Involuntary muscles
c) Striated muscles
d) Cardiac muscles
Answer: c) Striated muscles
Explanation:
- (a) Smooth – non-striated.
- (b) Involuntary – smooth/cardiac.
- ✅ (c) Skeletal muscles show alternating light & dark striations.
- (d) Cardiac – branched, involuntary.
Q3. The basic contractile proteins of skeletal muscle are:
a) Actin and myosin
b) Tubulin and keratin
c) Collagen and elastin
d) Hemoglobin and myosin
Answer: a) Actin and myosin
Explanation:
- ✅ (a) Actin (thin) & myosin (thick) → contraction.
- (b), (c), (d) – incorrect.
Q4. Which band remains constant during muscle contraction?
a) A band
b) I band
c) H zone
d) Sarcomere length
Answer: a) A band
Explanation:
- ✅ (a) A band = length of myosin → unchanged.
- (b) I band shortens.
- (c) H zone shortens/disappears.
- (d) Sarcomere length shortens.
Q5. The Z line is associated with:
a) Middle of A band
b) Middle of I band
c) Middle of H zone
d) End of sarcomere
Answer: b) Middle of I band
Explanation:
- ✅ (b) Z line lies in I band; two Z lines form sarcomere boundary.
Q6. Which region of sarcomere contains only actin filaments?
a) A band
b) I band
c) H zone
d) M line
Answer: b) I band
Explanation:
- ✅ (b) I band = thin filaments only.
- (a) A band = actin + myosin overlap.
- (c) H zone = myosin only.
- (d) M line = protein support.
Q7. The H zone is present in:
a) Centre of A band
b) Centre of I band
c) Centre of Z line
d) Centre of sarcolemma
Answer: a) Centre of A band
Explanation:
- ✅ (a) H zone = central part of A band, only myosin filaments.
Q8. Which protein masks actin binding sites in relaxed muscle?
a) Myosin
b) Tropomyosin
c) Troponin
d) Titin
Answer: b) Tropomyosin
Explanation:
- ✅ (b) Tropomyosin covers actin binding sites.
- (c) Troponin regulates tropomyosin.
- (d) Titin stabilizes myosin.
Q9. Which protein binds calcium ions during contraction?
a) Tropomyosin
b) Troponin-C
c) Myosin head
d) Actin
Answer: b) Troponin-C
Explanation:
- ✅ (b) Troponin-C binds Ca²⁺ → exposes actin sites.
Q10. The cross-bridge in muscle contraction is formed by:
a) Actin
b) Myosin heads
c) Tropomyosin
d) Titin
Answer: b) Myosin heads
Explanation:
- ✅ (b) Myosin heads attach to actin → cross-bridge cycle.
Q11. The light band of sarcomere is also called:
a) A band
b) I band
c) H zone
d) M line
Answer: b) I band
Explanation:
- ✅ (b) I band = isotropic, light under microscope.
Q12. Which line divides sarcomere into two halves?
a) Z line
b) M line
c) H line
d) I line
Answer: b) M line
Explanation:
- ✅ (b) M line passes through middle of sarcomere (center of A band).
Q13. Sarcolemma refers to:
a) Muscle fiber cytoplasm
b) Muscle fiber nucleus
c) Muscle fiber membrane
d) Myofibril
Answer: c) Muscle fiber membrane
Explanation:
- ✅ (c) Sarcolemma = plasma membrane of muscle fiber.
Q14. The cytoplasm of muscle cell is called:
a) Sarcoplasm
b) Sarcolemma
c) Sarcomere
d) Sarcoplasmic reticulum
Answer: a) Sarcoplasm
Explanation:
- ✅ (a) Sarcoplasm = muscle cytoplasm with myoglobin + glycogen.
Q15. The sarcoplasmic reticulum stores:
a) ATP
b) Calcium ions
c) Sodium ions
d) Potassium ions
Answer: b) Calcium ions
Explanation:
- ✅ (b) SR = reservoir of Ca²⁺ → released during contraction.
Q16. Which protein connects myosin filaments to Z line?
a) Actin
b) Troponin
c) Tropomyosin
d) Titin
Answer: d) Titin
Explanation:
- ✅ (d) Titin = giant elastic protein → stabilizes thick filaments.
Q17. Which region shortens during muscle contraction?
a) A band
b) I band
c) M line
d) Sarcolemma
Answer: b) I band
Explanation:
- ✅ (b) I band shortens due to actin-myosin overlap.
Q18. Dark band of striated muscle is:
a) A band
b) I band
c) H zone
d) Z line
Answer: a) A band
Explanation:
- ✅ (a) A band (anisotropic) appears dark.
Q19. The smallest structural unit of muscle visible under microscope is:
a) Myosin filament
b) Actin filament
c) Sarcomere
d) Myofibril
Answer: c) Sarcomere
Explanation:
- ✅ (c) Sarcomere = smallest contractile unit.
Q20. Muscle fibers are multinucleated because:
a) Fusion of myoblasts
b) Large size
c) Extra mitochondria
d) Thick sarcolemma
Answer: a) Fusion of myoblasts
Explanation:
- ✅ (a) Myoblast fusion → multinucleated muscle fibers.
Q21. Which filament is thinner in skeletal muscle?
a) Actin
b) Myosin
c) Tropomyosin
d) Titin
Answer: a) Actin
Explanation:
- ✅ (a) Actin = thin filament; myosin = thick.
Q22. Cross-striations in skeletal muscle are due to:
a) Alternating actin and myosin
b) Tropomyosin arrangement
c) Sarcolemma folds
d) Titin proteins
Answer: a) Alternating actin and myosin
Explanation:
- ✅ (a) Alternating light (I band) and dark (A band).
Q23. The skeletal muscle fiber is rich in:
a) Hemoglobin
b) Myoglobin
c) Keratin
d) Collagen
Answer: b) Myoglobin
Explanation:
- ✅ (b) Myoglobin = O₂-binding pigment in muscles.
Q24. The A band is made of:
a) Only actin
b) Only myosin
c) Both actin and myosin
d) Only tropomyosin
Answer: c) Both actin and myosin
Explanation:
- ✅ (c) A band includes overlapping actin & myosin filaments.
Q25. The repeating contractile unit in myofibril is:
a) Sarcomere
b) Actin
c) Myosin
d) M line
Answer: a) Sarcomere
Explanation:
- ✅ (a) Sarcomere = functional unit of myofibril.
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