Q.37 Which one of the following is not true for sliding filament model?

1. Shortening of I-band and H-zone with no effect on A-band
2. Shortening of I-band, A-band and H-zone
3. No change in I-band and H-zone with shortening of A-band
4. Shortening of I-band and A-band with no effect on H-zone

   The correct answer is No change in I-band and H-zone with shortening of A-band.

   Sliding Filament Model Basics

   The sliding filament model explains muscle contraction where actin (thin) filaments slide past myosin (thick) filaments, shortening sarcomeres without changing filament lengths.​

   Band Changes During Contraction

   • I-band (only actin): Shortens as actin filaments overlap more with myosin.

   • A-band (myosin length): Remains constant as thick filament length is unchanged.

   • H-zone (myosin without actin overlap): Shortens or disappears as actin invades this region.​

   Option Analysis

   • Option 1: “Shortening of I-band and H-zone with no effect on A-band” → True. Matches model exactly.​

   • Option 2: “Shortening of I-band, A-band and H-zone” → False. A-band doesn’t shorten.

   • Option 3: “No change in I-band and H-zone with shortening of A-band” → False (NOT TRUE). Both I-band/H-zone shorten; A-band stays same.

   • Option 4: “Shortening of I-band and A-band with no effect on H-zone” → False. H-zone shortens; A-band unchanged.

   ---

   The sliding filament model explains muscle contraction through sarcomere shortening, crucial for NEET/cell biology exams. This article solves Q.37 identifying the false statement about I-band, H-zone, and A-band changes.

   Sarcomere Band Structure

   • A-band: Full length of thick (myosin) filaments – unchanged in contraction.

   • I-band: Actin-only region between Z-lines and A-band edges – shortens.

   • H-zone: Central myosin region without actin overlap – disappears/shorten.​

   Correct Answer Explanation

   Option 3 is false: “No change in I-band and H-zone with shortening of A-band” contradicts the model where:

   • I-band always shortens

   • H-zone always shortens/disappears

   • A-band never shortens

   Visual Proof: During contraction, Z-lines move closer, squeezing I-bands and eliminating H-zones while A-band length stays constant.​

   Why Other Options Are True

   • Option 1: Perfectly describes model (I+H shorten, A constant).

   • Option 2: Wrong because A-band doesn’t shorten.

   • Option 4: Wrong because H-zone disappears.

   Exam Memory Trick

   “I&H Shrink, A Stays Same” – I-band + H-zone shorten, A-band constant. Perfect for matching questions!​