BIOLOGY WITH HAMZA · MDCAT REVISION
Support & Movement
Name: ____________________ Date: ______________
Recall first. Check second. Return to the ideas you missed.
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Learning targets
- Identify the structural bands and filaments of a sarcomere.
- Explain how calcium exposes actin-binding sites.
- Describe the roles of ATP in attachment, movement and relaxation.
Core notes
- Actin and myosin slide; the filaments themselves do not shorten.
- Calcium exposes actin sites through troponin and tropomyosin.
- ATP enables detachment, re-cocking and calcium reuptake.
- Recruitment and firing frequency determine whole-muscle force.
Read, cover and redraw
A muscle-fibre action potential begins.
Depolarisation enters the fibre.
The sarcoplasmic reticulum releases calcium.
Tropomyosin shifts away from actin sites.
Written recall
1. Which sarcomere band remains unchanged during contraction, and why?
2. Why does loss of ATP produce stiffness rather than immediate relaxation?
Apply the idea
1. During normal sarcomere shortening, which pattern is expected?
- A band stays approximately constant; I band narrows
- A band shortens; I band stays constant
- Both thick and thin filaments shorten
- Z lines move farther apart
My answer: _____ Reason: ____________________________________
2. In a muscle fibre, ATP becomes unavailable while many myosin heads are attached to actin. Which step is directly prevented?
- Binding of calcium to troponin in every case
- Detachment of those heads following ATP binding
- Formation of all actin filaments during development
- Transmission of the original nerve impulse
My answer: _____ Reason: ____________________________________
3. During a simple elbow-flexion movement, which description best fits the main antagonistic pair?
- Triceps contracts to pull the forearm towards the upper arm
- Both muscles pull the forearm in the same direction
- Biceps contracts while triceps relaxes sufficiently to permit movement
- Bones shorten to flex the joint
My answer: _____ Reason: ____________________________________
Answer key
Cover this section while attempting the questions.
Written recall
1. The A band remains constant because it represents the length of thick myosin filaments, which do not shorten.
2. ATP is required for myosin to detach from actin and for calcium to be pumped back into storage.
Applied questions
1. A — Filaments slide and overlap more. Thick filament length, represented by the A band, stays approximately constant, while the I band and usually the H zone narrow.
2. B — ATP binding to myosin permits its release from actin. Without ATP, attached cross-bridges persist; ATP is also required for later cycling and calcium pumping.
3. C — Biceps is a main elbow flexor and triceps a main extensor. Coordinated opposing muscle activity permits movement; muscles pull on bones rather than shortening them.