Chapter 3: Microscopy

Question 1

What is a light microscope?

Answer 1

• any kind of microscope that uses visible light to observe a specimen

Question 2

What is a compound light microscope?

Answer 2

• uses two lenses to magnify the image

Question 3

• What is the objective lens? (2)

Answer 3

• lens closest to the specimen
• magnifies between 10x - 100x

Question 4

What is the ocular lens? (2)

Answer 4

• the eyepiece
• magnifies by 10x

Question 5

On a compound microscope, how would we calculate the total magnification?

Answer 5

• multiply the power of the ocular lens by the objective lens
  EXAM Q
• so max resolution would be 1000x

Question 6

What are microscopes usually used for?

Answer 6

to view parasites, bacteria, protozoa

Question 7

What is resolution?

Answer 7

• the ability to distinguish fine detail and structure
• the ability to distinguish 2 points a certain distance apart
  ex. a resolving power of 4 nm means that 2 points can be distinguished if they are at least 4 mm apart

Question 8

What must pass between 2 objects in order for them to be seen as 2 separate things? (2)

Answer 8

• light
• it basically separates the specimen from the glass

Question 9

Why must light pass between the 2 objects so they can be seen separately?

Answer 9

• they need a short enough wavelength to fit between them

Question 10

What is the resolution general principle?

Answer 10

• the shorter the wavelength, the better the resolution

Question 11

What is an electron microscope?

Answer 11

• uses electrons instead of light
  (has its advantages!)

Question 12

Why would the electron microscope be more advantageous than the light microscope in some cases? (3)

Answer 12

• electrons travel in much shorter waves than light
• so the resolving power would be greater
• allows greater magnification (up to 500 000x)

Question 13

Since the electron microscope has greater magnification, what would it allow us to view? (2)

Answer 13

• viruses
• internal cell structures (cell wall, xmes, nucleus etc>)

Question 14

What are the two types of electron microscopes?

Answer 14

• transmission and scanning

Question 15

What are transmission electron microscopes (TEM) used to view?

Answer 15

• to see internal structures

Question 16

how do transmission electron microscopes work? (2)

Answer 16

1. Very thin slices can be cut from sample - thin sections
2. samples are generally stained with a metal (osmium, uranium) to make structures opaque to electrons

Question 17

What are scanning electron microscopes (SEM) used for?

Answer 17

• to see surfaces
• less powerful
• i believe that AFM is a scanning microscope

Question 18

What is the atomic force microscope (AFM) used for?

Answer 18

• used to see molecules

Question 19

How do atomic force microscopes (AFM)

Answer 19

• Uses a thin metal probe to scan specimen, revealing bumps and depressions

Question 20

How close can the following see an object?
- human eye
- Compound light microscope
- electron microscope

Answer 20

1) 0.2 mm
2) )0.2 μm
3) 2 nm

Question 21

Fun fact: what is the largest known bacteria, and how big is it?

Answer 21

• Thiomargarita magnifica
• 1-2 cm