Microscopy — OCR GCSE Biology
Test yourself on Microscopy with OCR GCSE practice questions.
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Microscopy explained
Learners prepare temporary mounts: a single layer of onion epidermis stained with iodine, or cheek epithelium stained with methylene blue, is placed on a clean slide and a coverslip is lowered at about 45 degrees with a mounted needle to avoid trapping air bubbles.
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The slide is viewed on a compound light microscope, starting on the lowest power objective (4x), focusing with the coarse knob then the fine knob, before moving to higher power. Biological drawings use unbroken pencil lines, no shading, accurate proportions, and state the total magnification (eyepiece x objective, e.g. 10 x 40 = 400x). Labels are straight, uncrossed lines touching the structure named, such as nucleus, cell wall and cytoplasm.
Your focus
- Prepare a temporary slide mount of plant or animal cells using suitable stains and bubble-free coverslip technique.
- Operate a compound light microscope systematically using coarse and fine focus across low and high power objectives.
- Produce an accurate, labelled scientific drawing of observed cells following standard biological drawing rules.
Microscopy exam tips
Marking Points
- Lower the coverslip slowly at an angle using a mounted needle so air bubbles are not trapped over the stained specimen.
- Begin viewing on the lowest power objective lens, focus with the coarse knob until the specimen appears, then sharpen with the fine knob before changing objective.
- Produce biological drawings with single unbroken pencil lines, no shading or cross-hatching, accurate proportions, and the total magnification stated.
- Draw straight, uncrossed label lines that touch the structure named, without arrowheads, and label only structures actually visible.
- Calculate total magnification by multiplying eyepiece magnification by objective magnification, e.g. 10 x 40 = 400x.
Examiner Tips
- 💡Calculate total magnification by multiplying the eyepiece lens magnification (typically 10x) by the objective lens magnification.
- 💡When asked to evaluate a biological drawing in an exam, check for uncrossed label lines, absence of shading, and clear continuous outlines.
Common Mistakes
- Using a thick tissue sample that overlaps several cell layers, so light transmission is poor and cellular detail is obscured; correct by peeling a single thin layer such as onion epidermis.
- Drawing with sketchy lines, artistic shading, or omitting the stated magnification; correct by using one continuous pencil line per outline and recording the total magnification.
- Focusing with the high-power objective first, which risks cracking the coverslip and damaging the lens; correct by focusing on low power, then moving to high power and using only the fine knob.