microscopes Flashcards
2 core practical
core practical - onion cells
what is the equipment needed?
microscope
toothpicks
cover slips
iodine tincture
pipettes
onion
microscope slides
kitchen knife
core practical-onion cells
what are the steps?
slice the onion as thin as possible
clean your microscope slide and cover slip
put the onion on the microscope slide and reposition with a toothpick
add a drop of iodine on the onion
put the cover slip on top of the onion and only add a bit of pressure to push it down
how to calculate magnification?
magnification=observed size/actual size
exam question-actual size
the nucleus of a cell viewed at x500 magnification has an image size of 2.4mm calculate the real size of nucleus
2.4/500
Ans x 1000
=4.8 micrometre
exam question-actual size
a leaf cell is observed at x400 magnification, the size of the image is 2cm calculate the real size of the cell
2/400=5x10^-3
Ans x 1000
=5micrometres
exam question-actual size
three adjacent onion cells are viewed under a microscope at x200 magnification the combined image size of all three cells is 75mm
assuming all the cells are the same size calculate the real size of a single onion cell
75/3=25
25/0.125
Ans x 100=125micrometre
exam question-observed size
a cell with a length of 0.05mm is observed at x200 magnification calculate the size of the image
200 x 0.05
=10mm
core practical-light microscope
what is the equipment needed?
sterile cotton bud
microscope slide
methylene blue stain
distilled water
coverslip
light microscope
core practical-light microscope
what are the steps?
use a sterile cotton bud move it over the inside of your mouth
smear the cotton bud over a small area in the centre of a clean microscope slide
allow the smear to air dry
place two drops of 1% methylene blue stain onto the smear and leave for 1 minute
rinse off the excess methylene blue
dry the slide and add a drop of distilled water to the stained smear
cover with coverslip and observe the cheek cell under the microscope use low power first
draw three cheek cells as seen under high power
what do electron microscopes use?
electron beams
why do electron microscopes use short wavelengths?
so it has better resolving power
how can electron beams be focused?
using electromagnetic lenses (electromagnets)
what is resolution?
the ability to distinguish clearly between two points
what is a light microscopes resolution?
0.2 micrometres or 200 nanometre
how does a light microscope produce images?
uses light rays to make the object visible
how does a transmission electron microscope produce images?
electrons that pass through strike a detector producing an image
how does a scanning electron microscope produce images?
beams of electrons reflect back onto a detector
what are the advantages of using a light microscope?
it is cheap and easy to use
what are the advantages of using a transmission electron microscope?
has a higher resolution
what are the advantages of using a scanning electron microscope?
has a higher resolution
what are the disadvantages of using a light microscope?
lower resolution
what are the disadvantages of using a transmission electron microscope?
expensive and requires more training
what are the disadvantages of using a scanning electron microscope?
also expensive
do specimens have to be dead or alive to be seen under a microscope?
can be both
why do you have to stain cells with iodine to see them under a microscope?
because cells are colourless this will make them look like they have colour and our eyes do not have a high resolution so this will help us see cell structures
