Biology - Microscopes

This is a document about light microscopes, EMs, CEMs and SEMs, it was a homework task. It is based on the OCR specification for AS Biology. Happy revising! =P

HideShow resource information
  • Created by: Re-Re
  • Created on: 12-01-13 23:11
Preview of Biology - Microscopes

First 372 words of the document:

Reianna Shakil L6EFBiology03/10/12
The preparation of specimens for microscopes can be drastic, and can produce artefacts.
Artefacts are things you see under a microscope, but aren't actually there in real life. This
could be due to something like an air bubble.
Magnification refers to how much bigger the image is than the actual specimen.
Resolution refers to how well a microscope distinguishes two different points that are
close together. If a microscope can't separate two objects, then increasing the
magnification won't help.
Light Microscopes
The optical microscope, often referred to as the "light microscope", is a type
of microscope which uses visible light and a system of lenses to magnify images of small
Optical microscopes are the oldest design of microscope and were possibly designed in
their present compound form in the 17th century.
Basic optical microscopes can be very simple, although there are many complex designs
which aim to improve resolution and sample contrast.
Historically optical microscopes were easy to develop and are popular because they use
visible light so that samples may be directly observed by eye.
Electron Microscopes
An electron microscope uses a beam of electrons to illuminate a specimen and
produce a magnified image.
An electron microscope (EM) has greater resolving power than a light-powered optical
microscope because electrons have wavelengths about 100,000 times shorter than
visible light (photons).
They can achieve better than 50 pm resolution and magnifications of up to about
10,000,000x whereas ordinary, non-confocal light microscopes are limited
by diffraction to about 200 nm resolution and useful magnifications below 2000x.
The electron microscope uses electrostatic and electromagnetic "lenses" to control the
electron beam and focus it to form an image.
These lenses are analogous to but different from the glass lenses of an optical
microscope that forms a magnified image by focusing light on or through the specimen.
Electron microscopes are used to observe a wide range of biological and inorganic
specimens including microorganisms, cells, large molecules, biopsy samples, metals,
and crystals.

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

Reianna Shakil L6EFBiology03/10/12
Industrially, the electron microscope is often used for quality control and failure analysis.
Modern electron microscopes produce electron micrographs, using specialised digital
cameras or frame grabbers to capture the image.
Scanning electron microscope (SEM)
A scanning electron microscope (SEM) is a type of electron microscope that produces
images of a sample by scanning over it with a high energy focused beam of electrons.…read more

Page 3

Preview of page 3

Here's a taster:

Reianna Shakil L6EFBiology03/10/12
5 Resolving power 0.1-0.2 nm. Resolving power 200-300 nm.
6 Image is coloured (natural colour of Image is black and white.
object is seen).…read more


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all resources »