The Electron Microscope

What is an electron microscope?

A microscope that uses a beam of electrons and electromagnets to magnify specimens.

Why can electron microscopes produce highly detailed images?

Electrons have much shorter wavelengths than visible light, giving higher resolution.

What is the role of the electron gun?

It shoots a beam of electrons at the specimen.

What controls the electron beam in an electron microscope?

Electromagnets.

What happens when electrons hit the specimen?

The electron beam scatters depending on the specimen’s structure.

How is the final image formed in an electron microscope?

Detectors collect scattered electrons and a computer creates an image called an electron micrograph.

What is an electron micrograph?

An image produced by an electron microscope.

Why must electron microscopes operate in a vacuum?

Electrons would collide with air particles and scatter.

Why must water be removed from specimens?

Water evaporates in a vacuum and would damage the specimen.

Why are specimens treated with chemicals before viewing?

To strengthen the specimen so the electron beam does not destroy it.

What is a Transmission Electron Microscope (TEM)?

A type of electron microscope that produces detailed images of the inside of specimens.

How are TEM specimens prepared?

Strengthened with chemicals, dehydrated, embedded in resin, and sliced very thinly.

Why are TEM specimens cut into thin slices?

So electrons can pass through the specimen.

What does a TEM image show?

Internal structures of the specimen.

What is a Scanning Electron Microscope (SEM)?

A type of electron microscope that produces detailed images of the specimen’s surface.

How are SEM specimens prepared?

Strengthened, dehydrated, and coated with a thin layer of gold.

Why are SEM specimens coated in gold?

Gold improves electron reflection and image quality.

What does a SEM image show?

The outside surface of the specimen.

What is the main difference between TEM and SEM?

TEM shows internal structures; SEM shows surface structures.

How does TEM scan the specimen?

A broad beam passes through the specimen.

How does SEM scan the specimen?

A fine beam scans across the surface systematically.

Which microscope gives a 3D-like surface image?

SEM

Which microscope gives a 2D image of internal structures?

TEM

What is the advantage of electron microscopes over light microscopes?

Much higher magnification and resolution.

What does resolution mean in microscopy?

The ability to distinguish two close points as separate.

Why are electron microscopes important in biology?

They allow scientists to study ultrastructure and tiny organelles in detail.

What is ultrastructure?

The detailed internal structure of cells seen with electron microscopes.