Microscopes

Question 1

Types of microscopes

Answer 1

Optical microscopes and electron microscopes

Question 2

What are the two types of electron microscope?

Answer 2

• Transmission electron microscopes (TEMs)
• Scanning electron microscope (SEMs)

Question 3

What is meant by ‘magnification’?

Answer 3

How much bigger a sample appears to be under a microscope than it is in real life

Question 4

What is meant by ‘resolution’?

Answer 4

The ability to distinguish between two points on an image (amount of detail)

Question 5

How does an optical microscope work?

Answer 5

Light from a light source underneath the specimen passes through

Question 6

What is the maximum magnification of an optical microscope?

Answer 6

x1500

Question 7

What is the maximum resolution of an optical microscope?

Answer 7

0.2 μm

Question 8

What are the pros of optical microscopes?

Answer 8

• Living specimens
• Colour image

Question 9

What are the limitations of optical microscopes?

Answer 9

• 2D image
• Poor resolution

Question 10

What do optical microscopes allow us to see?

Answer 10

Whole cells / tissues

Question 11

How does a transmission electron microscope work?

Answer 11

• Use electromagnets to trasmit a beam of electrons that pass through a thin section of a specimen
• Denser areas absorb more electrons so appear darker on the electron micrograph produced

Question 12

What is the magnification of transmission electron microscopes?

Answer 12

x1,500,000

Question 13

What is the resolution of transmission electron microscopes?

Answer 13

0.0002 μm

Question 14

What are the pros of transmission electron microscopes?

Answer 14

• Greater resolution

Question 15

What are the limitations of transmission electron microscopes?

Answer 15

• Needs to be in a vacuum so it specimen must be non-living
• Black and white image
• May contain artefacts due to complex staining procedures
• Specimens have to be very thin (1 cell thick)
• 2D image

Question 16

What do transmission electron microscopes allow us to see?

Answer 16

Organelles

Question 17

How does a scanning electron microscope work?

Answer 17

• A beam of electrons passes across the surface and scatter
• The pattern of scattering builds a 3D image depending on the contours of the specimen

Question 18

What is the magnification of a scanning electron microscope?

Answer 18

x1,500,000

Question 19

What is the resolution of a scanning electron microscope?

Answer 19

0.02 μm

Question 20

What are the pros of scanning electron microscopes?

Answer 20

• 3D image
• Specimen can be thicker
• Greater resolving power than optical microscopes

Question 21

What are the limitations of scanning electron microscopes?

Answer 21

• Lower resolution than TEMs
• Vacuum so specimen has to be non-living
• May contain artefacts due to complex staining procedures

Question 22

Why must the specimen in TEMs AND SEMs be in a vacuum?

Answer 22

So that particles in the air do not deflect the electrons out of the beam alignment

Question 23

What is meant a specimen containing ‘artefacts’?

Answer 23

There may be air bubbles, fingerprints, dust, etc due to complex staining process

Question 24

What is the formula for calculating magnification?

Answer 24

Magnification = image size / actual size

M = I / A

Question 25

What is the formula for calculating image size?

Answer 25

Image size = actual size x magnification

I = A x M

Question 26

What is the formula for calculating actual size?

Answer 26

Actual size = image size / magnification

A = I / M