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Micrometers and Nanometers in Biology

Sep 19, 2025

Overview

This lecture introduces micrometers and nanometers, explains unit conversions, and discusses the uses and limitations of light microscopes in biology.

Units of Measurement in Biology

  • One meter is divided into 1,000 millimeters (mm).
  • One millimeter equals 1,000 micrometers (μm).
  • One micrometer equals 1,000 nanometers (nm).
  • To convert millimeters to micrometers, multiply by 1,000.
  • To convert micrometers to nanometers, multiply by 1,000.
  • E. coli is about 1 micrometer long; typical ribosome is about 25 nanometers.

Light Microscopes: Features and Uses

  • Both early and modern light microscopes have an eyepiece lens, stage, and focusing dial.
  • Early microscopes could magnify 300×; modern light microscopes can magnify 1,000×.
  • Light microscopes can be used to observe living cells.
  • Stains are sometimes needed to see details but can kill cells.

Limitations of Light Microscopes

  • Biggest limitation is resolution, which is how clearly two close objects can be seen as separate.
  • Resolution is limited by the wavelength of visible light (400–700 nanometers).
  • Standard light microscopes have a resolution limit of about 200 nanometers.
  • Objects closer than 200 nanometers apart cannot be distinguished as separate using light microscopes.
  • Electron microscopes are used for higher resolution (discussed in another lecture).

Key Terms & Definitions

  • Micrometer (μm) — one-thousandth of a millimeter; used for measuring bacteria.
  • Nanometer (nm) — one-thousandth of a micrometer; used for measuring very small cell parts.
  • Resolution — the minimum distance between two objects where they can still be seen as separate.
  • Light microscope — a microscope that uses visible light to magnify biological specimens.

Action Items / Next Steps

  • Memorize the conversions between millimeters, micrometers, and nanometers.
  • Learn the definition of resolution for exams.
  • Prepare for a future lesson on electron microscopes and magnification.