Microscopes and Microscopy

Question 1

What are the 3 types of microscopes?

Answer 1

• optical microscopes
• transmission electron microscopes
• scnning electron microscopes

Question 2

How do light (optical) microscopes work?

Answer 2

Relies on lenses to focus a beam of light

Question 3

How do transmission electron microscopes work?

Answer 3

• 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

Question 4

How do scanning electron microscopes work?

Answer 4

Electrons do NOT pass through the specimen, instead cause secondary electrons to ‘bounce off’ the specimen’s surface and be focused on the screen

Question 5

Define photomicrograph

Answer 5

Photograph of the image seen using an optical microscope

Question 5

Which type of microscope produces a photomicrograph?

Answer 5

An optical microscope

Question 6

What are the benefits of using an optical microscope?

Answer 6

• linear magnification
• stains not required for coloured objects
• can be used to study whole living organisms

Question 7

What is a drawback of using an optical microscope?

Answer 7

It has a limited resolution

Question 8

Define electron micrograph

Answer 8

Electrons form an image that a photograph is taken of

Question 9

What microscopes produce electron micrographs?

Answer 9

• scanning electron microscopes
• transmission electron microscopes

Question 10

Describe the type of electron micrograph produced by a transmission electron microscope

Answer 10

• 2D
• black and white image

Question 11

State the benefits of a transmission electron microscope

Answer 11

• high magnification achieved
• 0.1 nm resolution
• ultrastructure (internal structure) seen

Question 12

State the drawbacks of a transmission electron microscope and a scanning electron microscope

hint: both have the same drawbacks

Answer 12

• need skill and training to use
• specimens have to be chemically fixed
• speciment must be viewed under a vacuum
• can’t study living things

Question 13

Describe the type of image produced by a scanning electron microscope

Answer 13

• 3D
• black and white image
• a computer can artificially add colour onto the image

Question 14

State the benefits of a scanning electron microscope

Answer 14

• whole specimen can be used
• higher magnification and resolution

Question 15

Define magnification

Answer 15

Describes how much larger an image appears when compared with the original object

Question 16

Define linear magnification

Answer 16

If a specimen is magnified x100, it appears to be x100 wider and x100 longer than it actually is

Question 17

Define resolution

Answer 17

The ability of an optical instrument to see or produce an image that shows fine details clearly

Question 18

What are the two different kinds of slides?

Answer 18

• wet mount
• stained slides

Question 19

Describe how to create a slide with a wet mount

Answer 19

1. Place a drop of water on the slide
2. Place your sample speciment in your drop of water
3. Set a cover slip over the sample specimen at a 45 degree angle

Question 20

Describe how to create a stained slide

Answer 20

1. Set a coverslip over the sample specimen at a 45 degree angle
2. Place 1 drop stain on the other side of the cover slip
3. The staining agent will begin to seep under the cover slip as the paper towel draws water out from the other side

Question 21

Define stain

Answer 21

Coloured chemicals that bind to other molecules in or on the specimen, making the specimen easy to see

Question 22

Define differential staining

Answer 22

Staining each subcellular structure differently so the structures are easily identifiable within a single preparation

Question 23

Describe how to prepare the specimens for electron microscopes

Answer 23

1. Chemically fix the specimen
2. Dehydrate it
3. Embedd it in wax
4. Use a special instrument to make very thin slices called sections
5. stained and mounted in special metal salts

Question 24

Define **graticules**

Answer 24

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

Question 25

What are **low power drawings**?

Answer 25

- better to use lower magnification lens - an outline of tissues - no individual tissues drawn

Question 26

What are **high power drawings**?

Answer 26

- better to use high magnification lens - individual cells drawn

Question 27

State the magnification formula

Answer 27

magnification = image size/ actual size

Question 28

# ** How many divisions does an eyepiece graticule have?

Answer 28

100

Question 29

What is the formula for eyepiece division length?

Answer 29

(no. of stage divisions x length of one stage division)/ no. of eyepiece divisions

Question 30

Explain how to calibrate an eyepiece graticule.

Answer 30

1. Place a stage micrometer on the stage of the microscope. 2. Line up one of the divisions on the eyepiece graticule with a fixed point on the stage micrometer. 3. Count the number of divisions on the eyepiece graticule that correspond with a set measurement on the stage micrometer. 4. Calculate the distance in micrometres of one division on the eyepiece graticule.