Microscopy Flashcards
What is magnification
How many times bigger the image produced by the microscope is than the real life object
What is resolution
The ability to distinguish between 2 objects that are close together (seeing two structures that are very close as two separate objects)
How to calculate magnification of a light microscope
Total magnification = Eyepiece lens magnification (10) x Objective lens magnification
Magnification equation
IAM triangle
Image size
Actual size Magnification
See images for labelled diagram of microscope
Description of Light microscope
- Use light to form an image
- Using light, it is difficult to distinguish between (resolve) two objects that are closer than the wavelength of light 500-650nm
- up to x2000 magnification, maximum resolution is 0.2pm
- Can be used to observe eukaryotic cells, nuclei & possibly mitochondria & chloroplasts. Cannot observe ribosomes, ER or lysosomes
Description of Electron microscope
- Use electrons to form an image
- This increases the resolution, giving more detail bc a beam of electrons has a much smaller wavelength than light.
- Can resolve 2 objects that are extremely close tg. Maximum resolution of 0.2nm (1000x greater than optical microscopes)
- Can observe small organelles sa ribosomes, ER & lysosomes
- 2 types of e microscopes: Transmission electron microscope, Scanning electron microscope
Advantages of Light microscope
- inexpensive to buy & operate
- small & portable
- simple sample preparation
- vacuum is not required
- natural colour of sample is seen (or stains are used)
- specimens can be living or dead
Disadvantages of Electron microscope
- expensive to buy & operate
- large & needs to be installed
- complex sample preparation which often distorts material
- vacuum is required
- black & white images produced (can only be coloured digitally)
- specimens must be dead
What are Scanning electron microscopes
- SEMs scan a beam of electrons across the surface of the specimen. This bounces off the surface & knocks off electrons from the specimen, which are detected in a cathode ray tube forming an image
- SEMs therefore form 3D images that show the surface of a specimen
- lower res images than TEMs. Magnification x500,000 or less
Advantages of Scanning electron microscope
- can be used on thick or 3D specimens
- allow external 3D structure to be observed
Disadvantages of Scanning electron microscope
- lower resolution than TEMs
- cannot be used on live specimen (unlike optical microscopes)
- do not produce a colour image (unlike optical microscopes)
What are Transmission electron microscopes
- TEMs use electromagnets to focus a beam of electrons, which is transmitted through the specimen
- Denser parts of the specimen absorb more electrons, making them appear darker on the final image
Advantages of Transmission electron microscope
- high resolution images = more detail
- internal structures can be seen
- magnification x1,000,000 or more
Disadvantages of Transmission electron microscope
- only used w very thin specimens or thin sections of an object
- cannot be used to observe live specimens bc of the vacuum inside the TEM plus all the water must be removed from the specimen
- lengthy treatment required to prepare specimens. Artefacts could be introduced - these look like real structures but are acc the results of preserving & staining
- do not produce a colour image & are in 2D