Topic 1 - Microscopes and Staining Flashcards
OCR
State the 8 parts of a light microscope
Eyepiece Lens + Objective lens Ocular Tube Stage Iris Diaphragm Light Source Fine focusing wheel (small one) Coarse focusing wheel (large one)
State 2 types of light microscopes
Light (optical) Microscope Laser scanning (confocal) Microscope
State 2 types of electron microscopes
Transmission Electron Microscope
Scanning Electron Microscope
What is a light (optical) microscope used to observe?
whole cells and tissues
What is a transmission electron microscope used to observe?
organelles (as electrons pass through the specimen)
What is a scanning electron microscope used to observe?
cell surfaces (as electrons bounce of the specimen)
What is a laser scanning (confocal) microscope used to observe?
An object at a certain depth within a cell
Which microscopes can be used to study living organisms?
Light (optical) microscope and laser scanning (confocal) microscope
Give two key points about light (optical) microscopes
1: Uses light (wavelength of 400-700 nm) which is focused by glass
2: image produced is called a photomicrograph
Give three advantages of light (optical) microscopes
1: Linear magnification of specimen
2: max magnification of x1500 to x2000
3: Stains don’t have to be used
(cheap, study living organisms, portable)
Give two disadvantages of light (optical) microscopes
1: Limited resolution (200nm)
2: Doesn’t show cell ultrastructure
Give two key points about laser scanning (confocal) microscopes
1: Laser light used and information is used to form an image on a computer screen
2: Emitted light is monochromatic (one wavelength)
Give three advantages of laser scanning (confocal) microscopes
1: High resolution + linear magnification
2: Microscope had depth selectivity
3: Can be used to study living organisms
Give two disadvantages of laser scanning (confocal) microscopes
1: Although magnification and resolution is high, it is still limited
2: Not easy to use - requires computer specialist
Give three key points about transmission electron microscopes
1: Uses beam of electrons (wavelength of 0.004 nm) from a cathode
2: Electrons pass through specimen and these are focused onto a screen by magnets/photographic plate
3: 2D black and white electron micrograph produced
What must be done to a specimen before it can be viewed using an electron microscope?
1: Specimens are fixed to preserve them
2: They are dehydrated (as electrons can heat the water)
3: embedded in wax and thin sections are prepared
4: they are examined in a vacuum
Give three advantages of a transmission electron microscope
1: Very high magnification ( x2000000)
2: 0.1nm resolution
3: Internal structure of thin specimen can be seen
Give three disadvantages of a transmission electron microscope
1: Large and expensive
2: Requires skill and training to use
3: Specimen must be dehydrated and examined in a vacuum
(cannot study living organisms)
Give three key points about a scanning electron microscope
1: Uses beam of electrons (wavelength of 0.004nm)
2: Electrons bounce of specimen
3: 3D electron micrograph is produced - colour may be added by a computer
Give three advantages of a scanning electron microscope
1: High magnification (x15 to x200000)
2: 0.1nm
3: whole specimen can be used and colour can be added
Give three disadvantages of a scanning electron microscope
1: Large and expensive
2: Specimen had to be coated in a metal film
3: Specimen had to be viewed in a vacuum
What is an eyepiece graticule?
A measuring device that acts as a ruler, superimposed on the specimen. It has 100 divisions.
What is a stage graticule?
Measuring device on the stage which is used for calibration.
Give the equation for the eyepiece division length
Eyepiece division length = Length of stage graticule/ Number of eyepiece divisions
