1.1 The Microscope in Cell Studies

Cambridge International AS Level Biology 9700

2026 📋 Syllabus Objectives

By the end of this topic, you should be able to:

  1. Make temporary preparations of cellular material suitable for viewing with a light microscope
  2. Draw cells from microscope slides and photomicrographs
  3. Calculate magnifications of images and actual sizes of specimens from drawings, photomicrographs and electron micrographs (scanning and transmission)
  4. Use an eyepiece graticule and stage micrometer scale to make measurements, and use the appropriate units: millimetre (mm), micrometre (µm) and nanometre (nm)
  5. Define resolution and magnification and explain the differences between these terms, with reference to light microscopy and electron microscopy

📏 Units of Measurement

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When studying cells, the structures are so tiny that everyday units like centimetres are far too large. We use three special units instead.

UnitSymbolSize (fraction of a metre)
Millimetremm1/1,000 of a metre (10⁻³ m)
Micrometreµm1/1,000,000 of a metre (10⁻⁶ m)
Nanometrenm1/1,000,000,000 of a metre (10⁻⁹ m)

Converting between units:

  • To go from mm → µm: multiply by 1000
  • To go from µm → mm: divide by 1000
  • To go from µm → nm: multiply by 1000
  • To go from nm → µm: divide by 1000

💡 Memory tip: Moving to a smaller unit = multiply by 1000. Moving to a larger unit = divide by 1000.

To give you a sense of scale:

  • The smallest thing visible to the naked (unaided) eye is about 50–100 µm
  • A typical human body cell is about 5–40 µm across
  • A typical bacterial cell is about 1 µm across
  • A ribosome (a tiny structure inside cells) is only about 25 nm in diameter — far too small to see without a special microscope

🔬 Objective 1: Making Temporary Slide Preparations

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A temporary slide preparation is a slide you make yourself in the lab so you can view cells under a light microscope. Unlike permanent slides (which are professionally made and can be used many times), temporary slides are made quickly for immediate use.

Why do we need to prepare slides?

  • Samples must be thin enough for light to pass through them
  • Stains are often used to make cell structures more visible, because many cell parts are colourless

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