Overview
This lecture covers the types of microscopy (light vs. electron), their differences, pros and cons, types of electron microscopy, and the concept of resolution in microscopy.
Types of Microscopy
- Two main types: light microscopy and electron microscopy.
- The primary difference is the source of radiation: light microscopes use visible light; electron microscopes use electron beams.
Light Microscopy
- Uses light as a source of illumination, producing colored images.
- Maximum useful magnification is up to 1500×.
- Allows observation of live or dead specimens.
- Magnifying lenses are made of glass.
- Total magnification = eyepiece lens magnification × objective lens magnification.
- Portable, inexpensive, and easy to operate.
- Mostly shows cell outlines but lacks detailed organelle visualization.
- Uses organic dyes for better clarity and color.
Electron Microscopy
- Uses an electron beam as the source of illumination, producing black and white images.
- Maximum useful magnification is up to 250,000×.
- Only dead specimens can be observed due to the vacuum chamber needed for operation.
- Requires metal stains and electromagnetic lenses for imaging.
- Not portable, very expensive, and requires skilled professionals.
- Provides detailed images of cell structures and organelles.
Types of Electron Microscopy
- Transmission Electron Microscope (TEM): The electron beam passes through a very thin specimen, producing 2D images.
- Scanning Electron Microscope (SEM): The electron beam scans the specimen surface, producing 3D images.
- Both produce images that are black and white, though computers can add color.
Magnification and Resolution
- Magnification refers to how much larger an image appears compared to the real object.
- Resolution is the minimum distance at which two points can be seen as separate entities.
- Light microscope resolution is about 200 nanometers; electron microscope resolution is about 0.5 nanometers.
- Resolution depends on the wavelength of the radiation used; shorter wavelength provides higher resolution.
Key Terms & Definitions
- Photomicrograph — Image taken with a light microscope.
- Electron micrograph — Image taken with an electron microscope.
- Condenser lens — Lens that focuses light onto the specimen.
- Resolution — Minimum distance between two points at which they are seen as separate.
- Vacuum chamber — Space inside an electron microscope with no air, needed to prevent electron scattering.
- Magnification — The factor by which an image size increases compared to the original.
- Objective lens — The primary lens in a microscope that magnifies the specimen.
Action Items / Next Steps
- Review diagram of microscope structure in your notes.
- Prepare for the extra class on Saturday at 12:00 p.m. or access the recording if unable to attend.