OCR · A-Level · Biology
Course version: H420 · Version from Sept 2025
(ii) the examination of stained sections or photomicrographs of skeletal…
Full specification wording
Plant and animal responses: (ii) the examination of stained sections or photomicrographs of skeletal muscle.
This clause asks you to examine skeletal muscle using stained sections or photomicrographs, so you must recognise tissue features from images rather than from a description.
Checked against the OCR H420 specification (opens in a new tab) on .
- Point 12 of 12
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
This clause asks you to examine skeletal muscle using stained sections or photomicrographs, so you must recognise tissue features from images rather than from a description. In a stained section, the stain makes structures visible: skeletal muscle fibres appear as long, parallel, unbranched cylindrical cells lying side by side in bundles. Each fibre is multinucleate, with several flattened nuclei pushed to the periphery just under the sarcolemma, unlike cardiac muscle (branched, centrally placed nuclei, intercalated discs) and smooth muscle (spindle-shaped, single central nucleus, no striations). Under higher magnification, alternating light and dark bands give the striped appearance, reflecting the arrangement of actin and myosin myofilaments into sarcomeres.
What earns the marks
- Recognises skeletal muscle fibres as long, parallel, unbranched cylindrical cells arranged in bundles.
- States that skeletal muscle fibres are multinucleate with nuclei located at the periphery beneath the sarcolemma.
- Identifies cross-striations (alternating light and dark bands) visible in stained sections or photomicrographs.
- Distinguishes skeletal muscle from cardiac muscle (branched fibres, intercalated discs, central nuclei) and smooth muscle (spindle-shaped, single central nucleus, no striations).
- Uses observed features from the image, such as nuclear position and fibre arrangement, to justify the identification rather than relying on the label alone.
- Interprets the magnification or scale bar to judge the size and detail visible in the photomicrograph.
Common mistakes and how to put them right
Assuming all muscle has a single central nucleus.
Put it right: Is that skeletal muscle fibres are multinucleate with peripheral nuclei.
Confusing skeletal with cardiac muscle because both show striations.
Put it right: Is that cardiac fibres branch and have intercalated discs, whereas skeletal fibres are parallel and unbranched.
Ignoring the scale bar or magnification when describing a photomicrograph.
Put it right: Is to use it to judge actual size and level of detail.
Treating the stain as the structure itself.
Put it right: Is that the stain merely makes features such as nuclei and bands visible for examination.
Exam tips
- Learn a comparison table of skeletal, cardiac and smooth muscle covering fibre shape, branching, nuclear number and position, and striations.
- Practise describing unfamiliar photomicrographs using the same checklist: shape, arrangement, nuclei, striations, scale.
- Always link each observation to the identification, for example peripheral nuclei plus parallel unbranched fibres indicate skeletal muscle.
Try the lesson
The start of the Plant and animal responses: (ii) the examination of stained sections or photomicrographs of skeletal muscle. lesson, made from checked teaching notes for this specification point.
Have a go first
In a stained transverse section of skeletal muscle viewed under the microscope, which feature shows that the fibres are arranged in bundles?
Listen
This clause asks you to examine skeletal muscle using stained sections or photomicrographs, so you must recognise tissue features from images rather than from a description. In a stained section, the stain makes structures visible: skeletal muscle fibres appear as long, parallel, unbranched cylindrical cells lying side by side in bundles. Each fibre is multinucleate, with several flattened nuclei pushed to the periphery just under the sarcolemma, unlike cardiac muscle (branched, centrally placed nuclei, intercalated discs) and smooth muscle (spindle-shaped, single central nucleus, no striations). Under higher magnification, alternating light and dark bands give the striped appearance, reflecting the arrangement of actin and myosin myofilaments into sarcomeres. A strong answer earns marks for these points. Recognises skeletal muscle fibres as long, parallel, unbranched cylindrical cells arranged in bundles. States that skeletal muscle fibres are multinucleate with nuclei located at the periphery beneath the sarcolemma. Identifies cross-striations (alternating light and dark bands) visible in stained sections or photomicrographs. Distinguishes skeletal muscle from cardiac muscle (branched fibres, intercalated discs, central nuclei) and smooth muscle (spindle-shaped, single central nucleus, no striations). A common slip: Assuming all muscle has a single central nucleus. Instead, is that skeletal muscle fibres are multinucleate with peripheral nuclei. Exam tip: Learn a comparison table of skeletal, cardiac and smooth muscle covering fibre shape, branching, nuclear number and position, and striations.
Key words
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Structure of skeletal muscle tissue
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Interpretation of stained sections and photomicrographs
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Comparison of muscle tissue types
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Using microscopical evidence to justify identification
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See every definition
- Structure of skeletal muscle tissue
- Long, parallel, unbranched cylindrical cells lying side by side in bundles, each multinucleate with flattened nuclei pushed to the periphery just under the sarcolemma.
- Interpretation of stained sections and photomicrographs
- Recognising tissue features from images, where the stain makes structures visible, and using observed features such as nuclear position and fibre arrangement to justify identification.
- Comparison of muscle tissue types
- Distinguishing skeletal muscle from cardiac muscle, which is branched with centrally placed nuclei and intercalated discs, and from smooth muscle, which is spindle-shaped with a single central nucleus and no striations.
- Using microscopical evidence to justify identification
- Using observed features from the image, such as nuclear position and fibre arrangement, to justify the identification rather than relying on the label alone.
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