Microscopes, Human Biology: Lab Procedures
Answer the questions on a separate piece of paper...
Part One. Set-Up and Image Orientation.
Use the overlapping thread slide you picked up for the set-up introduction.
1. Draw (and label!!) the three threads as they appear without the microscope.
2. Draw and label the three threads (make sure all three get into the drawing!) as they appear through the microscope at low power (4X lens, with 40X total magnification).
3. The microscope image looks different from the naked eye image due to the magnification of the microscope. Ignoring those differences, how else are the images different?
Part Two. Uses of Different Magnifications.
Take a slide with a whole preserved insect or crustacean. Look at it with the 4X, 10X, and 40X objective lenses (be careful at high power, these are often thick and the cover slip can be easily broken - some may already be cracked). Each power (40X, 100X, and 400X with the ocular figured in) has some advantages and some disadvantages over the other powers, some things it=s better for and some things it=s worse for. For each power, give one advantage and one disadvantage - that makes this a SIX-Part question.
Part Three. Staining cells.
Put the Part Two slide back and get a plain slide and cover slip. Wash and dry them well but carefully. Put a drop of water from a dropper on the slide - start with a fairly small drop of water. Use a toothpick from the lab table to lightly scrape the inside surface of your cheek (and the base of your teeth if you're feeling adventurous), then stir the tip of the toothpick in the drop. Place a cover slip on the drop and look for cells at low power (4X Lens, 40X magnification). Remember to close your iris diaphragm so they don't disappear against the light field. Once you have cells, work your way up to high power (40X Lens, 400X magnification). It=s best to stop at middle power and refocus rather than skipping past it.
1. Draw a single cheek cell as it looks at high power. Don't make the drawing too small.
Go down to middle power and refocus, then, with the slide still on the 'scope, "bleed" some stain under one edge of the cover slip. It should spread quickly; if not, add to the drop beside the cover slip or gently "suck" water from the opposite side of the cover slip with a bit of paper towel. Watch through the microscope as the stain reaches the cells.
2. Describe what happens as the stain reaches the cells.
Look for an area with obviously-stained cells against a mostly white background - with luck, you shouldn't have to bleed water through to lighten the surrounding stain.
3. How do the cells differ now from how they looked before?
4. If you had put the stain on as a first step, how much easier would finding the cells have been?
Clean and return the slide and cover slip. If you cannot get all of the stain off the slide (if if still has purple blotches), give the slide to Mr. McDarby.
Part Four. Sections of Tissue.
Obtain a Part Four slide. These are stained sections, thin slices through tissues that have been stained to make various details stand out. Looked at under the microscope, where the white background shows through was usually a space, outside or inside the organ/ structure. The staining properties of different cells or tissues, as well as the different types of cells, produce visible layers and regions.
1. Look at your section at low power (total magnification 40X). Briefly describe what you see in terms of spaces, layers, and other distinct visible features.
2. Go up to middle power (total 100X). Briefly describe what additional or changed features appear.
3. Go to high Adry@ (total 400X). Find an area where the edges of cells can be seen between stained nuclei (singular nucleus). Draw such an area, showing nuclei and cell membranes, and label those features. You donít have to show a large area, but enough to give context to the drawing. Remember, tissue is full of cells, each one in contact with the next. Staining rarely makes the membranes show up, so on these slides most of what you see is nuclei against a background color. There will be a few places where youíll see the fine lines of membranes between the nuclei, but youíll have to hunt for them.
Copyright 2012, Michael McDarby.
First version 1992, web version 2012.
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