2.1.1 Microscopy

Question 1

Features of a light microscope

Answer 1

• Low Resolution and magnification due to a longer wavelength
• Living organisms can be examined and a colour image is obtained

Question 2

Features of a Transmission Electron Microscope

Answer 2

• Dead samples can only be obtained
• Higher Magnification and Resolution
• Electrons are passed through a specimen using an electron gun
• Some parts of specimen absorb the electrons making it look darker
• 2D image and used to see internal structure
• Used in a vacuum

Question 3

Why can electron microscopes only use dead organisms?

Answer 3

• As electrons would be absorbed by the air and so the Electron microscope must be in a vacuum.

Question 4

Features of a Scanning Electron Microscope

Answer 4

• Produces a 3D image
• Electrons beamed onto the surface of the specimen and then reflect backwards in different ways depending on the contours

Question 5

The use of an eye piece graticule and stage micrometer?

Answer 5

• Used to measure the size of objects
• 1. Line up the stage micrometer and eye piece graticule
• 2. Count how many divisions can fit into one division of micrometer
• 3. Each division is 10 micrometers e.g. if there were 2 divisions in eye do 10/2 =5

Question 6

4 types of slide preparation for light microscopes

Answer 6

• Wet mount = Add water to the specimen before lowering coverslip with mounted needle so no air bubbles form
• Dry mount = thin slices/whole specimens are covered with just a coverslip on top
• Squash slide = Water added but add pressure to squash the sample to make it thinner in order for light to pass through
• Smear Slide = Place a drop of sample on one end, use another slide (place it at an angle) use to smear the sample evenly and smoothly. Cover slip is added

Question 7

What is resolution?

Answer 7

Minimum distance between two objects but both still seen as separate objects

Question 8

What is magnification?

Answer 8

How many times bigger the image of the specimen is compared to the actual size of image.

Question 9

Types of differential staining

Answer 9

Crystal Violet and Methylene blue = positive charged stains which are attracted to negative charges
Nigrosin and congo red = negatively charged, has a stained background and unsteadiness cells stand out.