Microscopes

Question 1

What are the 3 main types of microscopes?

Answer 1

• Scanning electron microscope
• Transmission electron microscope.
• Optical microscope.

Question 2

Magnification DEF

Answer 2

• How many times larger an image is compared to the actual object.

Question 3

Resolution Def

Answer 3

• The ability to distinguish between two points on an image ie amount of detail.

Question 4

What does the resolution of an image depend on in an electron vs light/ optical microscope?

Answer 4

• Light: depends on wavelength of light (long wavelength of light —> lower resolution.)
• Electron: wavelength of the beam of electrons (shorter wavelength of electrons –> higher resolution.)

Question 5

Resolution DEF

Answer 5

• The ability to distinguish between two points on an image.

Question 6

How does light microscope work?

Answer 6

• Light is condensed to create image.

Question 7

Advantages of light microscopes.

4 main advantages

Answer 7

• Coloured images.
• Can view living samples.
• No risk of artefacts.
• Simple sample prep

Question 8

Disadvantages of light microscopes.

give 2

Answer 8

• Lower resolution as light has longer wavelength than a beam of electrons.
• Lower magnification

Question 9

How do electron microscopes work IN GENERAL?

Answer 9

• Beam of electrons condensed to create image.
• Electromagnets are used to condense the beam.

Question 10

Specifically, how does SEM work?

Answer 10

• Electrons bounce off surface (scatter in different ways depending on the contours) of specimen and are condensed by electromagnets to create image.

() - extra information.

Question 11

Specifically, how does a TEM work?

Answer 11

• Electrons pass through thin specimen (some absorbed, some pass straight through.)
• Denser parts (of specimen) absorb more electrons (appear darker.) Parts where electrons gone straight through = white.

Question 12

Why must specimens under an electron microscope be in a vaccum? What does this explain?

Answer 12

• Because electrons are absorbed by air.
• This explains why only non-living specimens can be examined.

Question 13

Because electrons have a shorter wavelength than light, what advantage does this give both electron microscopes?

Answer 13

• Shorter wavelength = higher resolution (allowing internal structures/ smaller organelles to be observed.)

Question 14

When using SEM, do the specimens need to be as thin as when using a TEM microscope?

Answer 14

• No. Specimens don’t have to be AS thin.

Question 15

What images are produced by light (optical) microscope and a TEM microscope?

Answer 15

• 2D images.

Question 16

What images are produced by SEM microscope?

Answer 16

• 3D images.

Question 17

Which microscope allows to see specimen with colour?

Answer 17

• Light
• Both electron microscopes do not.

Question 18

What is the preparation of a sample like in light microscopes?

Answer 18

• Simple prep
• Can view live cells.

Question 19

Under which microscope can you view living specimens?

Answer 19

• Under the light/ optical microscope.

Question 20

What is the preparation of samples like under an SEM microscope?

Answer 20

• More complex staining process than light microscope but less than TEM (not as thin specimens need to be used.)

() - extra for clarification.

Question 21

What is the preparation of samples under TEM microscope like (in comparison to the other microscopes?)

Answer 21

• Much thinner specimens/ more time consuming.
• Complex staining process.

Question 22

What is the disadvantage of SEM and TEM microscopes in terms of artefacts? Advantage of light/ optical?

Answer 22

• Optical: N/A (no artefacts.)
• SEM: risk of artefacts
• TEM: highEST risk of artefacts.

Question 23

What are artefacts?

Answer 23

• Observations that appear on micropgraphs due to staining/ preparation that aren’t supposed to be part of the micrograph/ on the cell.

Question 24

Why is there no scale on the eyepiece graticule?

Answer 24

• Divisions on the eyepiece graticule scale will be different depending on magnification used.

Question 25

How do you calibrate the eyepiece graticule?

Answer 25

- Use a stage micrometer (glass slide with a scale on it.) - The scale on the stage micrometer is usually 2mm long/ each sub-division worth 10 micrometers.

Question 26

How do you work out the value of each small division on the eyepiece graticule?

Answer 26

- Line up the stage micrometer with the eyepiece graticule. -

Question 27

When would we need to recalibrate a microscope?

Answer 27

- When changing the magnification.

Question 28

What is the difference between a graticule unit and a smaller division?

Answer 28

- Graticule units: large units on eyepiece graticule. - Smaller divisions: the smaller units on eyepiece graticule.

Question 29

Which has higher resolution, SEM or TEM? What does this mean in terms of what can be seen?

Answer 29

- TEM has a higher resolution. - TEM: internal structures can be seen.

Question 30

Equation for determing the magnification?

Answer 30

Image size/ actual size.

Question 31

How to calculate mag?

Answer 31

Image size/ actual size.

Question 32

# Past Paper Why do we press down on the cover slip? Why do we use a thin tissue?

Answer 32

- Press down: thin layer of cells so light passes through. - Thin tissue: single, thin layer of cells.

Question 33

# Past Paper Describe how the student could use an eyepiece graticule to determine the mean diameter of stomata. 3 marks

Answer 33

- Measure using eyepiece graticule. - Calibrate eyepiece graticule against stage micrometer. - Take a no of measurments (to calculate a mean.)