This is an introduction to the microscope, and we’re going to not only how to use a microscope but also cover the basics of optics, slide preparation, and why we can see things that are invisible to the naked eye. Microscopes are basically two lenses put together to make things appear larger.
The first thing you need to do is select a compound microscope. While you can do these lessons without one, it’s really a totally different experience doing it with a scope. Cheap microscopes are going to frustrate you beyond belief, so here are the ones we recommend that will last your kids through college. You’ll want one with the optional mechanical stage (instead of stage clips), fine and coarse adjustment knobs, and at least three objectives.
If you’ve just purchased a microscope, keep it in its packaging until you watch the videos in this section. We’ll show you how to handle it, store it, and where not to touch. Your first job is to start collecting as many interesting windowsill insects as you can find.
Here are the scientific techniques we’re going to cover:
- The compound microscope is really just a set of lenses stacked so they work together to make things look bigger. For example, if you’re using a 10x eyepiece (where your eye looks into) and a 40x objective (the lens near the slide), then you’re using a 400x power setting.
- Not only is it important to learn how to work the scope, but you need to learn how to sketch what you see, or the information on the slide is only useful to one person – you. Make sure you always add a border (so your viewer knows where your drawing starts and ends), title (so you know what you were looking at), power of magnification (so you can do it again if needed), and keep your proportions accurate when you draw the image.
- You can use either a dry or wet mount to get your specimens ready for viewing. A dry mount doesn’t use any chemicals, water, or glue… and sometimes not even a coverslip. Just stick it on the slide and you’re god to go. This is a great place to start when first using a scope.
- A wet mount is used for living things, like the stuff found in pond scum. By keeping the organisms wet (and in their environment), you can watch how they move, eat, breathe, and interact. When specimens are hard to see (even after adjusting your diaphragm) you can use staining (like Lugol’s stain or dark iodine) to add contrast and bring it into view. Protoslo can be used when specimens move too fast to view.
- Heat fixes are used when the specimens move all over the place when stained (like yeast). By drying out the specimen and fixing it to the slide, you can easily stain it several times to bring out the contrast and view the structure. (Very good for viewing bacteria.)
- When you want to keep your specimens for a longer time (like a couple of months), apply a drop of superglue to the top of the slide before adding the coverslip. Press gently with a toothpick (not your fingers!) to squish out any bubbles.
- For any particular environment, some kinds of organisms survive well, some survive less well, and some cannot survive at all.
- Populations live in a variety of habitats, and change in those habitats affects the organisms living there.
By the end of the labs in this unit, students will be able to:
- Properly handle and care for a compound microscope.
- Identify the parts and optics of a microscope.
- Prepare a slide for observation using various slide preparation techniques.
- Differentiate observation from inference (interpretation) and know scientists’ explanations come partly from what they observe and partly from how they interpret their observations.
- Measure and estimate the weight, length and volume of objects.
- Formulate and justify predictions based on cause-and-effect relationships.
- Conduct multiple trials to test a prediction and draw conclusions about the relationships between predictions and results.
- Construct and interpret graphs from measurements.
- Follow a set of written instructions for a scientific investigation.