Module 2 Section 1 - Microscopy Flashcards
what is magnification
how much bigger the image is than the specimen (the sample your looking at)
what do microscopes produce
a magnified image
how is magnification calculated
magnification = image size / object size
what is resoultion
how well a microscope distinguishes between two separate points that are close together
if a microscope cant separate two separate objects then….
increasing the magnification wont help
what is the formula triangle which has image size, magnification and obejct size
image size
magnification x object size
what are three microscopes we need to know
-light microscopes
-laser scanning confocal microscopes
-electron microscopes
what does a light microscope use to form images
light
what is said about the resolution of light microscopes
lower than electron microscopes
what are light microscopes usually used for
whole cells or tissues
what is typically the maximum useful magnification of light microscopes
x1500
what do laser scanning microscopes use to from images
laser beams (usually tagged with fluorescent dye)
what does thee laser do the dye
gives off light - light is then focused through a pinhole onto a detector
what happens after light is focused on the detector
detector hooked up to a computer which generates an image - image can be 3D
what does the pinhole mean
any out of focus light is blocked meaning microscope produces a much clearer image
what can these microscopes also be for?
looking at different depths in thick specimens
what do electron microscopes use to form images
electrons
what two kinds of electron microscopes are there
-transmission electron microscope (TEM)
-Scanning electron microscope (SEM)
what do transmission electron microscopes use to form images
electromagnets to focus a beam of electrons which is transmitted through the specimen
why do some parts f TEM image look darker than others
because they are denser
why are TEMs good
they provide high resolution images
Why are TEMs not so good
Can only be used on thin specimens
How do SEMs form images
They scan a beams of electrons across a specimen which knocks off electrons from the specimen gathered in a cathode ray tube to form an image
Why are SEMs good
Shows the surface of the specimen and can be 3D
What is the maximum resolution of a light microscope
0.2 micrometers
What is the maximum resolution of TEMs
0.0002 micrometers
What is the maximum resolution of SEMs
0.002 micrometers
What is the maximum magnification of light microscopes
x 1500
What the maximum magnification of TEMs
Can be more than x1 000 000
What is the maximum magnification of SEMs
Usually less than x 500 000
Why do you need to stain samples
Objects being viewed may be transparent so you stain the sample so components of the cell can be viewed
What type of staining is used for light microscopes
Some sort of dye
Different stains …..
Are used to make different things show up. More than one stain can be used at once
What type of staining is used for electron microscopes
Objects are dipped in a solution of heavy metals
Why are sample for electron microscopes dipped in heavy metals
The metal ions scatter the electrons, again creating contrast
What do you need to view a specimen under a light microscope
A microscope slide
What are the different types of slides
Dry Mount
Wet Mount
What is a dry mount
A specimen that is placed on a slide with or without a coverslip over it.
What is wet mount
A specimen is placed on a drop of water on the slide, with a coverslip placed over it
What is the first stage of using a microscope
-Clip the slide on the stage
What is the second stage of using a microscope
Select the lowest powered objective lens
What is the third stage of using a light microscope
Use the coarse adjustment knob to bring the stage just below the objective lens
What is the fourth stage of using a light microscope
Look down the eyepiece, use the coarse adjustment knob to move the stage downwards until the image is roughly in focus
What is the fifth stage of using a light microscope
Adjust the fine adjustment knob to focus until a clear image shows
What is the sixth stage of using a light microscope
You can see the specimens under a greater magnification by swapping to a higher powered objective lens and refocus
What is the eyepiece graticule used for
Finding the size of the specimen
Where is the eyepiece graticule fitted
Onto the eyepiece
What is a stage micrometer used for
Used to work out the value of the divisions of the eyepiece graticule at a particular magnification
Why is the eyepiece graticule described as a transparent ruler
It is like a ruler but with no units or numbers
