Cell structure - microscopy

Question 1

What is a laser scanning confocal microscope?

Answer 1

Maximum magnification x2000
Maximum resolution 0.2 μm (200nm)
- In confocal microscopes, a single spot of focussed light is moved across a specimen. The specimens are labeled using antibodies with fluorescent tags.
- Advantages: Simple sample prep, specimen can be living or dead
- Disadvantages:
- Low magnification and resolution compared to electron microscope
- Expensive to buy

Question 2

What is a compound light microscope?

Answer 2

Maximum magnification x1500
Maximum resolution 0.2 μm (200nm
Advantages - Inexpensive, portable, simple sample prep, specimen can be living or dead
Disadvantages - Low magnification and resolution compared to electron microscopes.
Resolution is limited by the wavelength of light and diffraction of light as it passes through the sample.
Cells are often stained to increase contrast.

Question 3

What is a Scanning Electron Microscope (SEM)?

Answer 3

Magnification over x 500,000
Maximum resolution 2nm ( 0.002μm )
In an SEM a beam of electrons is sent across the surface of a specimen and the reflected electrons are collected.
- Advantages- High resolution / High magnification
- Disadvantages - Expensive to buy, large needs to be installed, complex sample prep, risk of artifacts, black and white images, specimens are dead

Question 4

What is a Transmission electron microscope (TEM)?

Answer 4

Magnification over x 1 000 000
Maximum resolution 0.5 nm (0.0005μm)
- In electron microscopy, a beam of electrons with a wavelength less than 1nm is used to illuminate the specimen. A higher resolution can be achieved because electrons have a much smaller wavelength than light.
- Advantages: High resolution, magnification
-Disadvantages - Expensive to buy and operate, large need to be installed, complex sample prep, risk of artifacts ( damage), black/white images, specimen is dead.

Question 5

Magnification equation :

Answer 5

Magnification = image size/object size

Question 6

What is magnification ?

Answer 6

• how much bigger the image is than the specimen (the sample you’re looking out )

Question 7

What is resolution ?

Answer 7

• is how detailed the image is

Question 8

Staining samples for light microscopes

Answer 8

• using a dye , common stains include methylene blue and eosin
• The stain is taken up by some parts of the object more than others- the constrast makes the different parts show up.
• Different stains are used to make different things show up. eosin use to stain cytoplasm , methylene blue stains DNA.
• More than one stain can be used at once .

Question 9

Staining samples for an electron microscope.

Answer 9

• Objects are dipped in a solution of heavy metals (like lead).
• The metal ions scatter the electrons, again creating constrast- some parts of the object show up darker than others .

Question 10

What are the two types of slide preparation ?

Answer 10

• Dry mount
• Wet mount

Question 11

How to prepare a dry mount ?

Answer 11

• Your specimen needs to let light through it for you to able to see it clearly under the microscope - Need to take a thin slice
• Use tweezers to pick up your specimen and put it in the middle of a clean slide.
• Pop a cover slip on top