biology : class11 I Band : Structure, Contractile Proteins, Muscle Fibre : Skeletal Muscle MCQ Questions and Answers
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I Band
MCQ questions and answers.
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MCQ Questions
1. In a relaxed skeletal muscle sarcomere, which structural description of the I band is most accurate?
A.
It contains only thin actin filaments and is bisected by a Z line
B.
It contains only thick myosin filaments and is bisected by an M line
C.
It contains overlapping actin and myosin filaments and lies between two M lines
D.
It contains the entire length of thick filaments and is bounded by two Z lines
Correct Answer:
It contains only thin actin filaments and is bisected by a Z line
Explanation:
The I band is the light region of a sarcomere containing thin actin filaments without overlap from thick myosin filaments. A Z line passes through its centre.
2. During contraction of a skeletal muscle fibre, which change specifically occurs in the I band?
A.
Its length increases because actin filaments move toward the Z lines
B.
Its length decreases because the Z lines move closer together
C.
Its length remains constant because the myosin filaments shorten
D.
It disappears because actin filaments are enzymatically degraded
Correct Answer:
Its length decreases because the Z lines move closer together
Explanation:
During contraction, thin actin filaments slide inward toward the M line, bringing the Z lines closer together and reducing the width of the I band.
3. Which observation would provide the strongest evidence that the I band represents a region without thick-filament overlap?
A.
The I band becomes narrower during contraction
B.
The I band is bisected by the Z line
C.
The I band contains actin filaments extending from the Z line
D.
The I band is lighter than the A band under a microscope
Correct Answer:
The I band contains actin filaments extending from the Z line
Explanation:
The I band consists of portions of thin filaments that do not overlap thick filaments. Its actin filaments are anchored to and extend away from the Z line.
4. If the distance between successive Z lines decreases while the length of the thick filament remains unchanged, which band change is expected most directly?
A.
The I band becomes shorter
B.
The I band becomes longer
C.
The I band changes into the H zone
D.
The I band remains unchanged because it contains myosin
Correct Answer:
The I band becomes shorter
Explanation:
A sarcomere shortens when its Z lines move toward one another. The I band, representing non-overlapping actin regions near the Z lines, consequently decreases in width.
5. A microscope image shows a light region crossed at its centre by a dense transverse line. Which interpretation correctly identifies both structures?
A.
The light region is the I band and the transverse line is the Z line
B.
The light region is the A band and the transverse line is the M line
C.
The light region is the H zone and the transverse line is the Z line
D.
The light region is the I band and the transverse line is the M line
Correct Answer:
The light region is the I band and the transverse line is the Z line
Explanation:
The I band is the lighter region containing only thin filaments, and the Z line runs through its middle, forming the boundary of adjacent sarcomeres.
6. Which molecular arrangement best explains why the I band becomes narrower without the actin filament itself becoming shorter?
A.
Actin filaments slide farther over one another at the Z line
B.
Actin filaments slide toward the M line while retaining their length
C.
Myosin filaments depolymerize and reduce the uncovered actin region
D.
Z lines dissolve, allowing the I band to contract independently
Correct Answer:
Actin filaments slide toward the M line while retaining their length
Explanation:
The I band narrows because thin actin filaments slide toward the centre of the sarcomere. The filaments themselves do not shorten; their position relative to thick filaments changes.
7. At the boundary between two adjacent sarcomeres, which arrangement involving the I band is correct?
A.
A single Z line lies between two I-band regions, one from each sarcomere
B.
A single M line lies between two I-band regions, one from each sarcomere
C.
An entire I band lies between two adjacent A bands without a Z line
D.
Two H zones meet directly at the boundary between adjacent sarcomeres
Correct Answer:
A single Z line lies between two I-band regions, one from each sarcomere
Explanation:
Each I band is bisected by a Z line. Since a Z line marks the boundary between adjacent sarcomeres, portions of the I bands of both sarcomeres lie on either side of it.
8. Which statement distinguishes the I band from the H zone in a sarcomere?
A.
The I band contains only actin, whereas the H zone contains only myosin
B.
The I band contains only myosin, whereas the H zone contains only actin
C.
The I band is bisected by the M line, whereas the H zone is bisected by the Z line
D.
The I band remains fixed during contraction, whereas the H zone lengthens
Correct Answer:
The I band contains only actin, whereas the H zone contains only myosin
Explanation:
Both regions lack filament overlap, but the I band contains the actin-only portions near the Z line, while the H zone is the myosin-only region around the M line.
9. A sarcomere is experimentally stretched beyond its resting length. Assuming the filaments remain intact, what is the most likely effect on its I band?
A.
The I band widens as the Z lines move farther apart
B.
The I band narrows as actin filaments slide toward the M line
C.
The I band disappears because actin overlaps all myosin
D.
The I band remains fixed because Z lines are not part of the sarcomere
Correct Answer:
The I band widens as the Z lines move farther apart
Explanation:
Stretching increases the distance between Z lines. This enlarges the regions containing actin without myosin overlap, so the I band becomes wider.
10. Which combination correctly predicts the I-band appearance and its response when a muscle fibre changes from a relaxed to a maximally contracted state?
A.
Light region; it becomes narrower but does not normally vanish completely
B.
Dark region; it becomes wider because myosin filaments shorten
C.
Light region; it becomes wider because actin filaments move away from the M line
D.
Dark region; it remains unchanged because actin and myosin are fixed in position
Correct Answer:
Light region; it becomes narrower but does not normally vanish completely
Explanation:
The I band appears light because it lacks thick-filament overlap. During contraction, actin slides inward and reduces the actin-only region, making the I band narrower; it is not normally eliminated entirely.
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