Light microscopes use visible light and glass lenses, whereas electron microscopes use a beam of electrons and electromagnetic lenses. Electron microscopes provide much higher resolution and useful magnification, revealing smaller cell structures, but require more complex specimen preparation.
This comparison is required at both SL and HL within A2.2 Cell structure.
| Feature | Light microscopy | Electron microscopy |
|---|---|---|
| Radiation source | Visible light | Beam of electrons |
| Lenses | Glass lenses | Electromagnetic lenses |
| Resolution | About 200 nm | Much higher; transmission electron microscopes can resolve structures below 1 nm |
| Magnification | Usually up to about ×1,500to×2,000 | Can exceed ×100,000 |
| Specimen | Living or dead specimens can be observed | Specimens are usually dead because conventional electron microscopy requires a vacuum |
| Preparation | Relatively quick; stains may be added | Complex; specimens may be fixed, dehydrated, sectioned or coated with metal |
| Image | Naturally coloured or stained; fluorescent stains may identify specific structures | Monochrome, although colour may be added digitally |
| Main use | Observing whole cells, tissues and living processes | Observing cell ultrastructure, including membranes, ribosomes and organelles |
In transmission electron microscopy (TEM), electrons pass through an extremely thin specimen. Dense regions absorb or scatter more electrons, producing a two-dimensional image of internal ultrastructure.
In scanning electron microscopy (SEM), an electron beam scans the specimen’s surface. Detected electrons produce a three-dimensional-looking image showing surface topography. Cryogenic electron microscopy can preserve specimens in a frozen, hydrated state, reducing some preparation artefacts.
A common misconception is that magnification and resolution mean the same thing. Magnification is how many times larger the image is than the specimen; resolution is the ability to distinguish two close points as separate. Increasing magnification without improving resolution produces only a larger blurred image.
Exam technique: For a “distinguish” question, give paired differences involving both microscopes. Examiners commonly reward the radiation source, resolution, specimen preparation and whether living specimens can be viewed; do not write only that electron microscopes “zoom in more.”
