methods of studying cells

Question 1

magnification

Answer 1

How much bigger a image is than the specimen

Question 2

Magnification=

Answer 2

image size/object size

Question 3

2 main types of microscopes

Answer 3

optical and electron

Question 4

Optical (light) microscopes

Answer 4

• use light to form image
• max resolution of 0.2 nanometres, organelles smaller than this can’t be viewed such as ribosomes
• max useful magnification is x 1500

Question 5

Electron Microscopes

Answer 5

• use electrons to form an image
• higher resolution to look at more organelles ( 0.0002)
• max magnification is about x1 500 000

Question 6

2 types of electron microscopes

Answer 6

Scanning and transmission

Question 7

How do Transmission (TEMs) microscopes work?

Answer 7

• uses electromagnets to focus a beam of electrons at the specimen
• denser parts absorb more electrons, so the image looks darker in some parts

Question 8

Why are TEMs better?

Answer 8

•give high resolution images, so you can see the internal structure of organelles

Question 9

Downsides of TEMs

Answer 9

•a very thin specimen

Question 10

How do Scanning (SEMs) microscopes work?

Answer 10

• a beam of electrons is fired at a specimen, causing electrons to knock off, these are collected in a cathode tube to produce an image
• image shows surface of specimen and can be 3 D

Question 11

Why are SEMs better?

Answer 11

can be used on thick specimens

Question 12

Downsides of SEMs

Answer 12

Lower resolution images than TEMs

Question 13

How do you prepare a temporary mount of a specimen on a slide?

Answer 13

• add a drop of water on to a slide using pipette
• using tweezers place a thin specimen on to the slide
• add a stain e.g. eosin to highlight chloroplasts and iodine in potassium iodide solution for starch
• using a coverslip, upright and tilt slowly to prevent air bubbles.