The light I band of skeletal muscle contains ____.
Correct answer D. only thin actin filaments
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MDCAT Biology MCQs
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Thin filaments of a sarcomere are anchored at the ____.
Correct answer C. Z line
In a relaxed muscle, which protein covers the myosin-binding sites on actin?
Correct answer D. Tropomyosin
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Each thin filament of skeletal muscle is composed mainly of ____.
Correct answer B. two twisted chains of actin with tropomyosin and troponin
During contraction of a sarcomere, which band or zone does NOT change in length?
Correct answer B. A band
What is the immediate role of ATP binding to the myosin head during the cross-bridge cycle?
Correct answer B. It causes the myosin head to detach from actin
Where on the contractile filaments is ATPase activity located?
Correct answer B. In the heads of myosin molecules
Which neurotransmitter is released at the neuromuscular junction to stimulate skeletal muscle?
Correct answer B. Acetylcholine
Rigor mortis, the stiffening of muscles after death, develops because ____.
Correct answer B. no ATP is available to detach myosin heads from actin
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Which compound in muscle rapidly regenerates ATP from ADP during the first few seconds of intense exercise?
Correct answer B. Creatine phosphate
A single motor neurone together with all the muscle fibres it supplies is called ____.
Correct answer C. a motor unit
A sustained, smooth contraction produced when stimuli arrive so rapidly that the muscle cannot relax between them is ____.
Correct answer C. tetanus
Fibrous bands of dense connective tissue that join bone to bone at a joint are ____.
Correct answer C. ligaments
The fluid that lubricates freely movable joints is secreted by the ____.
Correct answer B. synovial membrane
The joint between the atlas and the axis vertebrae, which allows rotation of the head, is a ____.
Correct answer B. pivot joint
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The hip and shoulder joints are examples of ____.
Correct answer B. ball-and-socket joints
The joint between the carpal and first metacarpal at the base of the thumb is a ____.
Correct answer C. saddle joint
The joint between the two pubic bones of the pelvis (pubic symphysis) is classified as a ____.
Correct answer D. cartilaginous joint
A few individuals colonise a new island and the new population has allele frequencies very different from the mainland. This is called ____.
Correct answer C. the founder effect
A natural disaster kills most of a population at random, leaving a few survivors with reduced genetic diversity. This is known as ____.
Correct answer D. the bottleneck effect