Microscopes Flashcards
Types of microscopes
Optical microscopes and electron microscopes
What are the two types of electron microscope?
- Transmission electron microscopes (TEMs)
- Scanning electron microscope (SEMs)
What is meant by ‘magnification’?
How much bigger a sample appears to be under a microscope than it is in real life
What is meant by ‘resolution’?
The ability to distinguish between two points on an image (amount of detail)
How does an optical microscope work?
Light from a light source underneath the specimen passes through
What is the maximum magnification of an optical microscope?
x1500
What is the maximum resolution of an optical microscope?
0.2 μm
What are the pros of optical microscopes?
- Living specimens
- Colour image
What are the limitations of optical microscopes?
- 2D image
- Poor resolution
What do optical microscopes allow us to see?
Whole cells / tissues
How does a transmission electron microscope work?
- Use electromagnets to trasmit a beam of electrons that pass through a thin section of a specimen
- Denser areas absorb more electrons so appear darker on the electron micrograph produced
What is the magnification of transmission electron microscopes?
x1,500,000
What is the resolution of transmission electron microscopes?
0.0002 μm
What are the pros of transmission electron microscopes?
- Greater resolution due to the wavelength of electrons being shorter than light
What are the limitations of transmission electron microscopes?
- Needs to be in a vacuum so it specimen must be non-living
- Black and white image
- May contain artefacts due to complex staining procedures
- Specimens have to be very thin (1 cell thick)
- 2D image
What do transmission electron microscopes allow us to see?
Organelles
How does a scanning electron microscope work?
- A beam of electrons passes across the surface and scatter
- The pattern of scattering builds a 3D image depending on the contours of the specimen
What is the magnification of a scanning electron microscope?
x1,500,000
What is the resolution of a scanning electron microscope?
0.02 μm
What are the pros of scanning electron microscopes?
- 3D image
- Specimen can be thicker
- Greater resolving power than optical microscopes
What are the limitations of scanning electron microscopes?
- Lower resolution than TEMs
- Vacuum so specimen has to be non-living
- May contain artefacts due to complex staining procedures
Why must the specimen in TEMs AND SEMs be in a vacuum?
So that particles in the air do not deflect the electrons out of the beam alignment
What is meant a specimen containing ‘artefacts’?
There may be air bubbles, fingerprints, dust, etc due to complex staining process
What is the formula for calculating magnification?
Magnification = image size / actual size
M = I / A
