2: CELLS - MICROSCOPES

Question 1

What is magnification?

Answer 1

how many times bigger the image is compared to the actual specimen

Question 2

What is resolution?

Answer 2

ability to distinguish between 2 points, resulting in greater level of detail observed

Question 3

What are the parts of an optical microscope and what do they do?

Answer 3

• eyepiece lens (you look through it)
• objective lens (used to change the magnification)
• coarse and fine focus adjustors (used to adjust the resolution)
• stage clip and stage (used to hold slide)
• mirror (used to reflect light onto the specimen)
• nosepiece (used to change objective lens)
• condenser (gathers light from light source and concentrates it onto the specimen being viewed)

Question 4

What are the 2 types of electron microscope?

Answer 4

• transmission electron microscope (TEM)
• scanning electron microscope (SEM)

Question 5

How does a transmission electron microscope (TEM) work?

Answer 5

• uses electromagnets to focus a beam of electrons which is then transmitted through the specimen
• denser parts of the specimen absorb more electrons so they appear darker in images
• specimen is placed in a vacuum
• complex prep of specimen (placed in fixing solution dehydrated and embedded in resin, sections cut using ultra-microtome)
• specimens must be non-living and thin

Question 6

How does an image from a TEM appear?

Answer 6

• 2D
• monochrome (black and white)

Question 7

How does a scanning electron microscope (SEM) work?

Answer 7

• beam of electrons scanned across specimen
• scattered electrons detected from surface of specimen
• specimen placed in a vacuum
• specimen must be non-living
• complex prep of specimen (coated in conductive material)

Question 8

How does an image from an SEM appear?

Answer 8

• 3D
• can be coloured

Question 9

What are the advs and disadvs of using a TEM (compared to using an SEM)

Answer 9

advs:
- higher resolution allows us to view internal structures of organelles
disadvs:
- can only be used on thin specimens
- 2D image
- can only be used on non-living specimens

Question 10

What are the advs and disadvs of using a SEM (compared to using an TEM)

Answer 10

advs:
- can be used on thicker specimens
- 3D images
disadvs:
- slightly lower resolution
- can only be used on non-living specimens

Question 11

What is the equation used to calculate magnification?

Answer 11

M=I/A
Magnification = image size/actual size

Question 12

How do you calculate magnification when given a scale bar?

Answer 12

• measure length of scale bar in mm
• convert length to μm
• magnification = scale bar image size / actual scale bar length (given to you in the question)

Question 13

How do you prepare a microscope slide?

Answer 13

• pipette a small drop of water onto the centre of the slide
• use tweezers to place a thin layer of the specimen onto the drop of water
• add a drop of a stain (eg: iodine solution)
• add a cover slip (stand it upright on the side then carefully tilt and lower it onto your specimen)

Question 14

What is an artefact?

Answer 14

things you can see when you look down the microscope that arent part of the specimen youre looking at (eg: dust, fingerprint, air bubbles)