cell structure - microscopes

Question 1

magnification

Answer 1

how many times larger an image appears compared to the actual size of the object

Question 2

resolution

Answer 2

a measure of how close 2 objects can be to still appear as 2 separate objects.

Question 3

the light microscope

Answer 3

max mag: x1500
resolution: 200nm
can be used to see: whole living organisms, tissues/cells from living organisms, colour images.

Question 4

why are specimens stained

Answer 4

to make them more visible
to increase contrast between organelles.

Question 5

differential staining

Answer 5

staining specific structures within the cell eg. Sudan red to stain lipids

Question 6

artefact

Answer 6

things that result from the way that the specimen is prepared, such as air bubbles.

Question 7

transmission electron microscope

Answer 7

transmits electrons through the specimen
magnification - x500000
resolution- 0.2-0.1nm
produces 2d image
specimen has to be dead and very thin because electrons are fired through a vacuum.
intracellular detail can be seen eg. vesicles

Question 8

scanning electron microscope

Answer 8

mag- x100000
res- 20nm
produces 3d image
electrons fired through vacuum so specimen has to be dead. Electrons reflected off specimen so doesn’t need to be as thin as TEM
surface detail can be seen eg. cell surfaces

Question 9

disadvantages of electron microscopes

Answer 9

images may contain artefacts
specimens have to be dead
complex staining process required
need a lot of skill for TEM

Question 10

how to prepare slide with onion epidermis

Answer 10

1. add 2 drops of water to clean microscope slide
2. peel off 1 cell thick piece of onion epidermis
3. lay it flat on microscope slide
4. add 2 drops of iodine
5. slowly lower cover slip over the top using a mounted needle
6. blot off any surplus stain
7. observe using light microscope. use lowest power objective lens.