Studying Cells - Using Microscopes (pages 18 - 19) Flashcards
In Light Microscopes and TEMs, you need to stain your samples, why? please explain in detail.
the beam of light (or electrons) passes through the object being viewed, an image is produced because some parts of the object absorb more light (or electrons) than others.
Sometimes the object being viewed is completely transparent. This makes the whole thing look white because the light rays (or electrons) just pass straight through.
so to get around this problem, the object can be stained.
For light microscopes object samples, what dye is used for staining objects?
common stains include Methylene blue and eosin.
Explain what happens once the stain is put onto the object ready to view under the light microscope?
the stain is taken up by some parts of the object more than others - the contrast makes the different parts show up.
Different stains are used to make different things show up, give an example what objects are used with the stain Eosin and Methylen Blue?
eosin is used to stain cell cytoplasms.
Methylene blue is used to stain DNA
(more than one stain can be used at once)
see diagram 1 on page 18 of Eosin stained specimen seen through a light microscope.
Is staining used for Electron Microscopes, and if yes, what is used?
for staining for the electron microscope, objects are dipped in a solution of heavy metals (like lead), the metal ions scatter the electrons, again creating contrast - some parts of the object show up darker than others.
what colour image is viewed with Electron Micrographs?
images are always black and white even when stained, but colour can be added artificially after the image has been made.
You need to know how to prepare a microscope slide.
What is a slide?
a slide is a strip of clear glass or plastic. Slides are usually flat, but some of them have a small dip or well in the centre (useful if your specimen’s particulary big or a liquid).
What are the two main ways of preparing a microscope slide?
Dry mount
Wet mount
Explain what Dry Mount preparing a micscrope slider mean process is?
Your specimen needs to let light through it for you to be able to see it clearly under the microscope. So if you’ve got quite a thick specimen, you’ll need to take a thin slice to use on your slide.
use tweezers to pick up your specimen and put it in the middle of a clean slide
pop a cover slip (a square of thin, transparent plastic or glass) on top.
Explain how to prepare a Wet Mount microscope slide process?
Start by pipetting a small drop of water onto the slide. then use tweezers to place your specimen on top of the water drop.
put the cover slip on, stand the 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 bubbles under there - they’ll obstruct your view of specimen.
Once the cover slip is in position, you can add a stain. Put a drop of stain next to one edge of the cover slip. Then put a bit of paper towel next to the opposite edge. The stain will get drawn under the strip, across the specimen.
What are Wet Mounts good for viewing?
good for looking at tiny organisms that live in water.
You are expected to be able to use a light microscope to view a specimen.
Explain the process how to use a light microscope to view a specimen?
1) Start by clipping the slide containing the specimen you wan to look at onto the stage.
2) Select the lowest-powered objective lens (i.e. the one that produces the lowest magnification).
3) Use the coarse adjustment knob to bring the stage up to you just below the objective lens.
4) Look down the eyepiece (which contains the ocular lens)
5) Adjust the focus with the find adjustment knob, until you get a lear image of whats on the slide.
6) If you need to see the slide with greater magnification, swap to a higher-powered objective lens and refocus.
If you are asked in an exam to draw what you can see under the microscope, dont forget to write down a very important thing, what is it?
always remember to write down the magnification the specimen was viewed under.
(remember you will also need to label your drawing)
see diagram 1 on page 19 for description of the microcope parts.
If you need to know the size of your specimen, what parts of the microscope do you need to measure this?
The eyepiece graticule and stage micrometer. (they are a bit like rulers)
Describe what an eyepiece graticule is?
it is fitted onto the eyepiece. Its like a transparent ruler with numbers, but no units.
Describe what the stage micrometer is and how to use it on a microscope?
The stage micrometer is placed on the stage - it is a microscope slide with an accurate scale (it has units) and it’s used to work out the value of the divsions on the eyepiece graticule at a particular magnification.
This means that when you take the stage micrometer away and replace it with the slide containing your specimen you’ll be able to measure the size of the specimen. look at diagram 2 on page 19 of example.
Explain the process of how you measure the size of the specimen with the sgate micrometer?
1) Line up the eyepiece graticule and the stage micrometer.
2) Each division on the stage micrometer is 0.1 mm long
3) At this magnification, 1 division on the stage micrometer is the same as 4.5 divisions on the eyepiece graticule.
4) To work out the size of 1 division on the eyepiece graticule, you need to divide 0.1 by 4.5:
1 division on eyepiece graticule = 0.1 ÷ 4.5 = 0.022 mm
5) So if you look at an object under the microscope at this magnification and its 20 eyepiece divisions long, you know it measures: 20 x 0.022 - 0.44 mm
(remember at a different magnification, 1 division on the stage micrometer will be equal to a different number of divisions on the eyepiece graticule - so the eyepiece graticule will need to be re-callibrated).
a) A microscope is set up with an eyepiece graticule and a stage micrometer. Each division on a stage micrometer is 10 µm long. At x 10 magnification, 1 division of the stage micrometer is equal to 6.5 divisions on the eyepiece graticule. Calculate the size of 1 division on the eyepiece graticule. Give your answer to the nearest 0.1 µm (2 marks)
b) A specimen is viewed under this microscope at x 10 magnification. It is 14 eyepeice divisions long. Use your answer to part a) to calculate the specimen’s length. Give your answer to the nearest µm (2 marks)
a) 10 ÷ 6.5 = 1.5 µm (2 marks for the correct answer or 1 mark for the correct calculation).
b) 14 x 1.5 = 21 µm (1 mark for multiplying 14 by answer to part a, 1 mark for an answer of 21 or 22 µm
