Microscopy Flashcards
Light Microscopes
• first developed in the mid 17th century
• use light and lenses to form an image of a specimen and magnify it
• let us see individual cells and large sub cellular structures, e.g. nuclei
• best can magnify about x 2000, school only a few hundred
• cheap
• can be used almost anywhere
• used on live specimens
Electron Microscopes
• invented in 1930s
• use a beam of electrons to from an image up to x 2,000,000
• allow biologists to study more sub cellular structures
• large
• very expensive
• higher magnification AND resolution
• can see ribosomes and plasmids
• have to be kept at special temperature, pressure and humidity controlled rooms
Calculating the magnification of an image - formula
magnification = image size / real size
OR
image size = magnification x real size
Units of measure microscope
1000 um = 1mm
1000 nm = 1um
How prepare an onion slide under a light microscope
1) Add a drop of water to the middle of a clean slide.
2) Cut up an onion and separate it out into layers. Use tweezers to peel off some epidermal tissue from the bottom of one of the layers.
3) Using the tweezers, place the epidermal tissue into the water on the slide.
4) Add a drop of iodine solution. Iodine solution is a stain. Stains are used to highlight objects in a cell by adding colour to them. (Makes them stand out)
5) Place a cover slip (a square of thin, transparent plastic or glass) on top. To do this, stand the cover slip upright on the slide, next to the water droplet. Then carefully tilt and lower it so it covers the specimen. Try not to get any air bubble under there - they’ll obstruct your view of the specimen.
Using a light microscope to look at your slide
1) Clip the slide you’ve prepared onto the stage.
2) Select the lowest powered objective lens (I.e. the one that produces the lowest magnification)
3) Use the course adjustment knob to move the stage up to just below the objective lens.
4) Look down the eyepiece. Use the course adjustment knob to move the stage downwards until the image is roughly in focus.
5) Adjust the focus with the fine adjustment knob, until you get a clear image of what’s on the slide.
6) If you need to see the slide with greater magnification, swap to a higher powered objective lens and refocus.
What is mounting?
• Placing the object onto a small sheet of glass.
What does a cover slip do?
• Protect the sample
What magnification is the eye piece lens usually?
x 10
Give a reason why you might look at the slide from the side.
• To make sure that the objective will clear the slide
• To make sure the lens doesn’t crash through the specimen and get damaged
How can you alter the illumination?
The microscope rheostat control can be found on the side of the compound microscope body. It will typically be a knob that is turned clockwise in order to increase the light intensity, or counter-clockwise to reduce the light.
What is resolution?
The ability to distinguish between two separate points.
It is the resolving power of a microscope that affects how much detail it can show.
