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.