microscopes

Question 1

explain light microscopes
(3)

Answer 1

they have two lenses - eyepiece and objective lens

the total magnification: magnifying power of the objective lens x the magnifying power of the eyepiece lens

light microscopes are limited by the wavelength of light
- they can only see detail where parts are more than 200nm (max resolution) apart
- this means that they can’t see the details of the organelles within the cells as the parts are too close together

Question 2

explain electron microscopes
(4)

Answer 2

they use a beam of electrons instead

their maximum resolution is about 0.5nm

they can have a maximum magnification of about x1000000

there are two types:
- scanning electron microscopes that make 3d images of the surface of the specimen
- transmission electron microscopes that can make 2d images through a specimen

Question 3

label the light microscope (11) oh

Answer 3

1 - eyepiece lens
2 - body tube
3 - coarse adjustment screw
4 - fine adjustment screw
5 - high power objective lens
6 - low power objective lens
7 - arm
8 - stage
9 - condenser
10 - mirror
11 - base

Question 4

explain the microscopy required practical

Answer 4

aim - using a light microscope to observed draw and label cells in onion skin

apparatus:
a small piece of onion
a knife
a white tile
forceps
a microscope slide
a coverslip
a microscope
iodine solution in dropper bottle

method: MAKING SLIDE
1. with a dropping pipette put one drop of water onto the slide
2. Separate one of the thin layers of onion from the inner surface
3. Use forceps to put the thin layer onto the drop of water on the slide
4. Make sure the layer of onion is flat on the slide
5. Put two drops of iodine onto the Onion tissue
6. Lower the cover slip onto the slide carefully
7. Use a piece of filter paper to soak up any liquid from around the edge of the cover slip
8. Put the slide on to the microscope stage

method: USING MICROSCOPE
1. Turn the nose piece to the lowest power objective lens
2. Turn the coarse adjustment knob so that it’s almost touching the slide ( look from the side)
3. Looking through the eyepiece turn the coarse adjustment knob in the direction to increase the distance between the lens and the slide ( do this until the cells come into focus)
4. Rotate the nosepiece to a higher power objective lens
5. Turn the fine adjustment to bring the cells into clear focus

method: DRAWING CELLS
1. On a piece of plain paper make a clear label drawing of the cells you have found
2. Use an eyepiece graticule to measure the length of one of the epidermal cells that you have drawn (include units)
3. Now measure the same cell in your drawing
4. Calculate the magnification of your drawing and write this underneath it
5. Magnification = length of drawing of cell/actual length of cell