Part 3: Muscle Contraction Mechanism – Sliding Filament Theory, Ca²⁺, ATP
Part 3 (25 MCQs) on Muscle Contraction Mechanism – Sliding Filament Theory, Ca²⁺, ATP from Chapter 20: Locomotion and Movement (NCERT Class 11 + NEET UG relevance).
Part 3: Muscle Contraction Mechanism – Sliding Filament Theory, Ca²⁺, ATP
Q1. The sliding filament theory of muscle contraction was proposed by:
a) Huxley and Niedergerke
b) Darwin and Wallace
c) Watson and Crick
d) Schleiden and Schwann
Answer: a) Huxley and Niedergerke
Explanation:
- ✅ (a) They proposed sliding filament theory (1954).
- (b), (c), (d) – unrelated.
Q2. During muscle contraction, which bands shorten?
a) A band only
b) I band and H zone
c) A band and I band
d) A band and H zone
Answer: b) I band and H zone
Explanation:
- ✅ (b) I band + H zone reduce; A band constant.
Q3. Which ion is essential for muscle contraction?
a) Na⁺
b) K⁺
c) Ca²⁺
d) Mg²⁺
Answer: c) Ca²⁺
Explanation:
- ✅ (c) Ca²⁺ binds troponin → shifts tropomyosin → exposes actin sites.
Q4. The immediate source of energy for muscle contraction is:
a) Glucose
b) ATP
c) Creatine phosphate
d) Glycogen
Answer: b) ATP
Explanation:
- ✅ (b) ATP hydrolysis at myosin head provides energy.
- (c) Creatine phosphate regenerates ATP, but not direct.
Q5. Which protein regulates actin–myosin binding?
a) Tropomyosin and troponin
b) Titin and myosin
c) Actin and ATPase
d) Myoglobin and collagen
Answer: a) Tropomyosin and troponin
Explanation:
- ✅ (a) Troponin binds Ca²⁺ → tropomyosin shifts → actin-myosin bind.
Q6. Which enzyme activity is present in myosin head?
a) ATPase
b) Kinase
c) Ligase
d) Transferase
Answer: a) ATPase
Explanation:
- ✅ (a) Myosin head hydrolyzes ATP → contraction.
Q7. Rigor mortis occurs due to:
a) Excess ATP
b) Lack of ATP
c) Excess calcium
d) Lack of oxygen
Answer: b) Lack of ATP
Explanation:
- ✅ (b) No ATP → myosin remains bound to actin → stiffness.
Q8. During muscle relaxation, Ca²⁺ is actively pumped into:
a) Sarcolemma
b) Sarcoplasm
c) Sarcoplasmic reticulum
d) Mitochondria
Answer: c) Sarcoplasmic reticulum
Explanation:
- ✅ (c) SR stores Ca²⁺ again, allowing relaxation.
Q9. Which event directly causes power stroke in muscle contraction?
a) ATP hydrolysis
b) Release of ADP + Pi from myosin head
c) Binding of ATP to myosin head
d) Binding of Ca²⁺ to troponin
Answer: b) Release of ADP + Pi from myosin head
Explanation:
- ✅ (b) Power stroke occurs when ADP + Pi are released.
Q10. Which band remains unchanged during contraction?
a) I band
b) A band
c) H zone
d) Sarcomere length
Answer: b) A band
Explanation:
- ✅ (b) A band (length of thick filaments) remains constant.
Q11. The cross-bridge cycle ends when:
a) ATP binds to myosin
b) Ca²⁺ binds to troponin
c) ADP binds to actin
d) Na⁺ enters muscle fiber
Answer: a) ATP binds to myosin
Explanation:
- ✅ (a) New ATP binding → myosin detaches from actin.
Q12. The latent period of muscle contraction is:
a) Time between stimulus and response
b) Time of contraction
c) Time of relaxation
d) Recovery period
Answer: a) Time between stimulus and response
Explanation:
- ✅ (a) Latent period = delay before contraction starts.
Q13. Excitation–contraction coupling in muscle involves:
a) Ca²⁺ release from SR
b) ATP release
c) Troponin degradation
d) Creatine phosphate breakdown
Answer: a) Ca²⁺ release from SR
Explanation:
- ✅ (a) Electrical excitation → SR releases Ca²⁺ → contraction.
Q14. What initiates depolarization of sarcolemma in skeletal muscle?
a) ATP
b) Acetylcholine
c) Ca²⁺
d) Na⁺
Answer: b) Acetylcholine
Explanation:
- ✅ (b) Acetylcholine at neuromuscular junction depolarizes sarcolemma.
Q15. Which structure transmits action potential deep into muscle fiber?
a) Sarcolemma
b) T-tubules
c) Sarcoplasmic reticulum
d) Myofibrils
Answer: b) T-tubules
Explanation:
- ✅ (b) T-tubules carry impulse deep → SR release Ca²⁺.
Q16. During contraction, actin filaments move:
a) Toward Z line
b) Toward M line
c) Away from sarcomere
d) Stay fixed
Answer: b) Toward M line
Explanation:
- ✅ (b) Actin slides inward toward M line, shortening sarcomere.
Q17. Which step in muscle contraction requires ATP hydrolysis?
a) Cross-bridge formation
b) Power stroke
c) Cocking of myosin head
d) Release of Ca²⁺ from SR
Answer: c) Cocking of myosin head
Explanation:
- ✅ (c) ATP hydrolysis energizes myosin head for power stroke.
Q18. Which molecule acts as oxygen reservoir in muscle?
a) Hemoglobin
b) Myoglobin
c) Actin
d) Troponin
Answer: b) Myoglobin
Explanation:
- ✅ (b) Myoglobin stores O₂ in muscles.
Q19. Which part of myosin interacts with actin?
a) Tail
b) Head
c) Neck
d) M line
Answer: b) Head
Explanation:
- ✅ (b) Myosin head binds actin, hydrolyzes ATP.
Q20. The energy for detachment of cross-bridge comes from:
a) ATP hydrolysis
b) ATP binding
c) ADP release
d) Ca²⁺ binding
Answer: b) ATP binding
Explanation:
- ✅ (b) ATP binding to myosin → detachment from actin.
Q21. Which statement about sliding filament theory is correct?
a) Filaments shorten during contraction
b) Sarcomere shortens, filaments slide
c) A band shortens, I band constant
d) Actin length decreases
Answer: b) Sarcomere shortens, filaments slide
Explanation:
- ✅ (b) Filaments slide, sarcomere shortens.
Q22. In absence of Ca²⁺, muscle contraction fails because:
a) ATP cannot bind
b) Myosin cannot hydrolyze ATP
c) Actin binding sites remain blocked
d) Myosin heads disappear
Answer: c) Actin binding sites remain blocked
Explanation:
- ✅ (c) Without Ca²⁺, tropomyosin covers binding sites.
Q23. Which neurotransmitter stimulates muscle contraction?
a) Dopamine
b) Acetylcholine
c) Norepinephrine
d) Serotonin
Answer: b) Acetylcholine
Explanation:
- ✅ (b) ACh at neuromuscular junction triggers contraction.
Q24. What causes rigor mortis after death?
a) Excess Ca²⁺ and no ATP
b) Excess ATP
c) Depletion of Ca²⁺
d) Low myoglobin
Answer: a) Excess Ca²⁺ and no ATP
Explanation:
- ✅ (a) Ca²⁺ leaks → contraction, but no ATP → relaxation impossible.
Q25. Which of the following is required for initiation of muscle contraction?
a) Na⁺ efflux from sarcolemma
b) Ca²⁺ binding to troponin
c) ATP release from mitochondria
d) Tropomyosin degradation
Answer: b) Ca²⁺ binding to troponin
Explanation:
- ✅ (b) Ca²⁺ binds troponin-C → exposes actin binding sites.
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