RP microscopy Flashcards
magnification equation
image size/actual size
eyepiece lens
lens closest to your eye, usually has a magnification of x10
objective lens
three lenses of different strengths, can be used to magnify image more clearly
stage
place where you put a microscope slide
diaphragm
controls amount of light that goes onto microscope slide
light/mirror
projects light onto the microscope slide
arm
holds eyepiece lens above stage
base
stop microscope from falling over
fine focus knob (smaller knob)
used to focus image to improve sharpness
coarse focus knob (larger knob)
used to focus image so you can see it clear
total magnification equation
magnification of eyepiece x magnification of objective
(e, l) magnification
electron has a higher magnification (x1000000), light is about (x450 to x600) so electron allows you to see much smaller things in more detail
(e,l) price
light microscope much cheaper (£70), compared to electron at £10,000
(e,l) colours
light microscope allows you to see in colour, electron is in black and white
what do light microscopes use to form an image?
light and lenses
what do electron microscopes use to form an image?
electrons
(e,l) resolution
electron have a higher resolution
resolution
the ability to distinguish between two points
method to prepare
- add a drop of water to middle of a clean slide
- cut up an onion and separate into layers and use tweezers to peel off some epidermal tissue
- add a drop of iodine solution to stain and highlight cells
- place a cover slip on top by slowly lowering down, try to reduce air bubbles
- place the slide on the stage of the microscope
method to observe
- turn the nosepiece to select a low power objective
- set up the microscope-use the coarse knob to raise the stage so the end of the objective lens almost touches it
- turn the coarse adjustment knob to move the lens towards the slide
- look through eyepiece and turn coarse adjustment knob until the cells come into focus
- slightly turn the fine adjustment knob to bring the cells into a clear focus
- turn the nosepiece to switch to a higher power
- use the fine adjustment knob again to bring the cells back into focus
- make a clear, labelled drawing of some of the cells, include the magnification
safety
- iodine is an irritant-wear goggles, wash hands
equipment list
-microscope
-onion
-iodine solution
-slide
-tweezers
-water
-cover slip
-scalpel
why is a thin sample of tissue required?
allows light to pass through so internal structures can be observed
why is water added to the slide?
allows the sample to be suspended between the slide and cover slip and ensures cover slip stays in place
why is iodine solution added?
it binds to starch in plant cells and stains it blue-black making sub-cellular structures easier to see
why is the cover slip lowered using a mounting needle?
to ensure that no air bubbles are trapped
define magnification?
the number of times bigger an image appears compared to the size of the real object
how does a light microscope work?
passes a beam of light through a specimen which travels through the eyepiece lens
5 advantages of light microscopes
inexpensive
easy to use
portable
in colour
living and dead specimens observed
disadvantages of light microscope
limited resolution
how does an electron microscope work?
uses a beam of electrons which are focused using magnets, electrons hit a fluorescent screen which emits visible light producing an image
2 advantages of electron microscopes
greater magnification and resolution
how have electron microscopes enabled scientists to develop their understanding of cells?
-allow sub-cellular structures to be observed in detail
-enable scientists to develop more accurate explanations
4 disadvantages of electron microscopes
expensive
large so less portable
black and white
training to use
only observe dead specimens
what stain is used for cheek cells?
methylene blue
