Microscopes and Microscopy Flashcards
What are the 3 types of microscopes?
- optical microscopes
- transmission electron microscopes
- scnning electron microscopes
How do light (optical) microscopes work?
Relies on lenses to focus a beam of light
How do transmission electron microscopes work?
- uses a beam of fast travelling electrons with a wavelength of 0.004nm fired from a cathode
- the beam of electrons passes through the specimen
- some pass through and are focused on the screen/ photographic plate
How do scanning electron microscopes work?
Electrons do NOT pass through the specimen, instead cause secondary electrons to ‘bounce off’ the specimen’s surface and be focused on the screen
Define photomicrograph
Photograph of the image seen using an optical microscope
Which type of microscope produces a photomicrograph?
An optical microscope
What are the benefits of using an optical microscope?
- linear magnification
- stains not required for coloured objects
- can be used to study whole living organisms
What is a drawback of using an optical microscope?
It has a limited resolution
Define electron micrograph
Electrons form an image that a photograph is taken of
What microscopes produce electron micrographs?
- scanning electron microscopes
- transmission electron microscopes
Describe the type of electron micrograph produced by a transmission electron microscope
- 2D
- black and white image
State the benefits of a transmission electron microscope
- high magnification achieved
- 0.1 nm resolution
- ultrastructure (internal structure) seen
State the drawbacks of a transmission electron microscope and a scanning electron microscope
hint: both have the same drawbacks
- need skill and training to use
- specimens have to be chemically fixed
- speciment must be viewed under a vacuum
- can’t study living things
Describe the type of image produced by a scanning electron microscope
- 3D
- black and white image
- a computer can artificially add colour onto the image
State the benefits of a scanning electron microscope
- whole specimen can be used
- higher magnification and resolution
Define magnification
Describes how much larger an image appears when compared with the original object
Define linear magnification
If a specimen is magnified x100, it appears to be x100 wider and x100 longer than it actually is
Define resolution
The ability of an optical instrument to see or produce an image that shows fine details clearly
What are the two different kinds of slides?
- wet mount
- stained slides
Describe how to create a slide with a wet mount
- Place a drop of water on the slide
- Place your sample speciment in your drop of water
- Set a cover slip over the sample specimen at a 45 degree angle
Describe how to create a stained slide
- Set a coverslip over the sample specimen at a 45 degree angle
- Place 1 drop stain on the other side of the cover slip
- The staining agent will begin to seep under the cover slip as the paper towel draws water out from the other side
Define stain
Coloured chemicals that bind to other molecules in or on the specimen, making the specimen easy to see
Define differential staining
Staining each subcellular structure differently so the structures are easily identifiable within a single preparation
Describe how to prepare the specimens for electron microscopes
- Chemically fix the specimen
- Dehydrate it
- Embedd it in wax
- Use a special instrument to make very thin slices called sections
- stained and mounted in special metal salts
Define graticules
Small disc with an engraved ruler
–> can be placed into the eyepiece of a microscope to act as the ruler in the field of view
What are low power drawings?
- better to use lower magnification lens
- an outline of tissues
- no individual tissues drawn
What are high power drawings?
- better to use high magnification lens
- individual cells drawn
State the magnification formula
magnification = image size/ actual size
**
How many divisions does an eyepiece graticule have?
100
What is the formula for eyepiece division length?
(no. of stage divisions x length of one stage division)/ no. of eyepiece divisions
Explain how to calibrate an eyepiece graticule.
- Place a stage micrometer on the stage of the microscope.
- Line up one of the divisions on the eyepiece graticule with a fixed point on the stage micrometer.
- Count the number of divisions on the eyepiece graticule that correspond with a set measurement on the stage micrometer.
- Calculate the distance in micrometres of one division on the eyepiece graticule.
