Cells

Question 1

Optical microscope

Answer 1

Type of electromagnetic radiation: light in the visible spectrum.
0.5 um to 1mm
Limited resolution power.
2D
Able to see natural colour and living specimens.
Thin specimen required.
Cheap cost
Small and portable.

Question 2

Transmission electron microscope

Answer 2

Transmission: 2D effect
A beam of electrons is focused onto the specimen by a condenser electromagnet. The beam passes through a thin section of the specimen and appears bright- other parts absorb the electrons and appear darker. The image produced on the screen is a photomicrograph.
The resolving power is 0.1nm but this can’t always be achieved because difficulties preparing the specimen limits the resolution achieved and a higher energy electron beam is required which may destroy the specimen.
Limitations:
Living specimens can’t be observed because the whole system must be in a vacuum.
A complex staining process is required and even then the image isn’t in colour.
Extremely thin specimen.
May contain artefacts.

Question 3

What’s an artefact?

Answer 3

Things that result from the way the specimen is prepared. Artefacts may appear in the finished photomicrograph but are not part of the natural specimen. It’s therefore not easy to be sure that what we see on a photomicrograph really exists in that form.

Question 4

The scanning electron microscope.

Answer 4

Lower resolving power than TEM (20nm).
3D image
All the limitations of the transmission electron microscope also apply to this microscope except the specimen doesn’t need to be as thin as electrons don’t penetrate. It directs a beam of electrons onto the specimen from above rather than below and the beam is then passed back and forth across a portion of the specimen in a regular pattern. The electrons are scattered by the specimen and the pattern of the scattering depends on the contours of the specimen surface. A 3D image can be created by computer analysis of the pattern of scattered electrons + secondary electrons produced.