Cells

Question 1

Light microscopes?

Answer 1

• use light form an image
• max resolution = 0.2 micrometres
• can’t see organelles smaller than 0.2 e.g. ribosomes/the endoplasmic reticulum/lysosomes
• max useful magnification = x 16500

Question 2

Electron microscopes?

Answer 2

• use electrons to form an image
• more detailed image + more organelles
• max resolution = 0.0002 micrometres
• max useful magnification = x 1,500,000
• black and yt images produced

Question 3

Transmission electron microscopes (TEMs)?

Answer 3

• use electromagnets to focus beam of electron -> transmitted thru specimen
• denser parts of specimen absorb more electron so - look darker on image
• can only view in a vacuum so - no good for living organisms

Question 4

Scanning electron microscopes (SEMs)

Answer 4

• scan a beam of electrons across specimen - knocks off electrons from specimen -> electrons gathered in cathode ray tube - to form image
• image show surface of specimen

Question 5

Advantages of TEMs v SEMs

Answer 5

TEMs: give high resolution images so - shows small objects
SEMs: can be used on thick specimens
- can be 3D

Question 6

Disadvantages of of TEMs v SEMs

Answer 6

TEMs: only used on thin specimens
- only used on non-living specimens
SEMs: give lower resolution images than TEMs
- only used on non-living specimens

Question 7

Steps for preparing microscope slides?

Answer 7

1. pipette small drop of water onto centre of slide
2. use tweezers to place a thin section of your specimen on top of the water drop aka ‘temporary/wet mount’ (specimen needs to let light through to be able to see it clearly)
3. Add a. drop of a stain. (used to highlight objects in a cell)
4. add the cover slip (protects the specimen) - stand slip upright on the slide, next to the water droplet -> carefully tilt and lower it so it covers the specimen (no air bubbles under there - obstruct view of the specimen)