2.1.1 Cell Structure

Question 1

A)What are the microscopes you need to know

Answer 1

• light/optical microscopes
• Transmission electron microscopes
• Scanning electron microscopes

Question 2

A)what does a light ( optical ) microscope do

Answer 2

• they helps to understand cell structure
• optical microscopes uses light (wavelength 400-700 nm) which is focused by glass.
• the photo of the image produced is called a photomicrograph

Question 3

A) what are the advantages of using a light / optical microscopes

Answer 3

• linear magnification (x50 means 50 times larger)
• cheap
• easy to use
• portable
• stains are not necessary

Question 4

A) what are the disadvantages of a light/optical microscope

Answer 4

• limited resolution so some organelles cannot be seen ( eg ribosomes)

Question 5

A) how does a transmission electron microscope work

Answer 5

• a beam of electron ( wavelength 0.004nm) from a cathode passes through the specimen and are focused by magnets onto a screen/photographic plate
• produces a 2B black and white photomicrograph

Question 6

A) what are the advantages to transmission electron microscopes

Answer 6

• very high magnification ( x2 000 000 max)
• 0.1 nm resolution
• Ultrastructure seen

Question 7

A) what are the disadvantages of transmission electron microscopes

Answer 7

• large
• expensive
• needs skills and training to use
• specimen needs to be in a vacuum
  -specimens needs to be dehydrated and stained with metal salt (may be dangerous)

Question 8

A) How does a scanning electron microscope work

Answer 8

• use of a beam of electrons from a cathode ( 0.004nm wavelength) that bounces of a specimen and then focussed by magnets.
• this makes a 3D black and white electron micrograph ( colour can be added by computer)

Question 9

A) what are the advantages of using a scanning electron microscope

Answer 9

• high magnification achieved (x15 - x200,000)
• 0.1 nm resolution
• whole specimen can be used

Question 10

A) what are the disadvantages of scanning electron microscopes

Answer 10

• large
• expensive
• need skill and training to use
• cannot be used to study living organisms
• specimen needs to be viewed while in a vacuum

Question 11

B) how do you prepare the wet mount slide for light microscopes

Answer 11

• place a drop of water on the slide
• place your sample specimen in your drop of water
• set a cover slip over the sample specimen at a 45 degree angle

Question 12

B) how do you prepare the stained slides for light microscopes

Answer 12

• Set a cover slip over the sample specimen at a 45o angle.
  -Place 1 drop stain on the other side of the cover slip.
  -The staining agent will begin to seep under the cover slip as the paper towel draws water out from the other side.

Question 13

B) what and how does an eye piece graticule work

Answer 13

• an eye piece graticule is a small transparent ruler used to see the size of the object you are looking at

Question 14

B) what is a stage micrometre

Answer 14

a microscope slide with a slide divided scale marked on the surface used to calibrate the eye piece graticule

Question 15

(c) what are stains

Answer 15

stains are coloured chemicals that bind to molecules which allows the different structures in specimens to become more visible

Question 16

(C) what is meant by differential staining

Answer 16

using different stains which are used so different tissues are stained different colours