Microscope use Exercises

These exercises will give you an opportunity to practice finding objects under the microscope, changing objective lenses, and focusing while learning how to make simple wet mount slides to observe. The exercises are organized by types of materials that may be readily available, or are appropriate to particular the class you are taking. Using one or more of the categories can provide interesting insights into and comparisons of the microscopic world at our hands.

You will inspect your slide under low (4X objective), medium (10X objective) and high (40 or 43X objective). What are the total magnifications you will achieve with these objectives?

| Cheek Cells | Pond Protozoans | Insect Parts | Plant Parts | Beef | Cytoplasmic Streaming |


Cheeky cells

1. Perhaps the easiest slide to make consists of cells from the inner wall of your own cheek.

a. With a clean toothpick, gently scrape the inside of your cheek. Swirl the toothpick in a couple of drops of water on a clean slide.

b. Gently lower a cover slip over the cells

2. Things to do and questions to ponder

a. Find a sheet of cells. Describe the general shape of individual cells.

b. Do you see any inner structure? What are those elongated oval things in the middle of every cell?

c. Why are some of these cells folded over (unlike plant cells in exercise d.)?

d. If you look in you mouth, your cheek is pink. Why aren't these cells pink?

Pond Protozoans

1. Get some water from the Puddle, or an aquarium. Plants from these waters will be useful for a comparison between sssthem and protozoans. (What is a protozoan?!)

a. Take your protozoan sample from the bottom, or near vegetation or rocks. Why? Think microhabitat.

b. Back at the lab, obtain some methyl cellulose from the stockroom. Make a ring of methyl cellulose on a slide. Place a drop or two of your water sample inside the ring.

c. Place a cover slip over your preparation.

2. Things to do and questions to ponder

Protozoans are one-celled organisms. They can move in and out of your field of view pretty fast! Locate some slowed individuals near the ring of methyl cellulose.

a. How many different kinds of protozoans do you find? Each kind (species, generally) will have a sssdifferent shape.

b. How are those guys moving around?! Adjust the light intensity to see flagella or cilia at high sssmagnification. How do the different kinds use their locomotor structures? That is, does the flagellum pull or push?

c. Why are some of these critters green and others unpigmented?

 

The One-Minute Entomologist: Insect Parts


If you have never closely inspected the morphology of an insect, you are in for an eye-opening treat. No computer-generated, imaginary life form can top Mother Nature. And to think that these little critters have musculature, circulatory and respiratory systems, too!


Part 1: The Aphid that ate Carnegie!

1. Obtain an insect. Live, minute aphids infest the underside of some plant leaves outdoors or in the Carnegie Greenhouse.

a. Live (!) aphids can be mounted in water under a cover slip. Try to mount one insect face up, and the other face down. (OK, so where IS an aphid's face??)

b. Place a few grains of fine sand on the slide before putting on the cover slip to prevent squishing your insect (yuck!).

c. Locate the aphid(s) under low power.

2. Things to do and questions to ponder

a. Check out the gross morphology (overall body structure). Unlike spiders, how many legs do insects have?

b. What are those other appendages? Find the long antennae, and under medium power, check out the shape of terminal end of an antenna. You will have to use the fine focus a lot to view this highly 3-dimensional specimen.

c. At the posterior end, find two exhaust-pipe like "cornicles," typical of most aphid species.

d. Do you see the hooked tarsal claws at the end of the legs, and the piercing mouthpart? How do aphids feed on plants (chew leaves or suck juices)?

e. Sometimes you can see internal movements from the underside of small specimens under medium power.


Part 2: Crispy Critters

Live insects can be humanely killed by placing them in a freezer overnight (sometimes in less time). Alternatively, find a dead insect. Even in the wintertime, you can find dead specimens on windowsills here and there. These specimens will be crispy and break apart easily, but do not despair! You will only need a small section of a body part to mount.

1. For insects without obvious wings (but again, not all insects have wings- can you name one that does not?): Lift off the wing covering carefully with a pin. Tease out a piece of the membranous wing below.

2. Mount its wings and legs or antennae in water with a cover slip.

3. Things to do and questions to ponder:

a. Do you see what look like hairs? Inspect the structure of these "hairs" under high power. Why do they have no obvious cellular structure? (Neither does your hair-check it out!)

b. Under low power, do you observe venation in the wing? Some insects, such as wasps and flies, are identified to species by the unique pattern of wing venation.

c. If you have a moth or butterfly wing, look for the scales that cover and give color to the wing.

 

Get Personal with a Plant


1. Visit the department greenhouse. The department maintains a large variety of plants, common and otherwise.
sSpecific plants are maintained in the greenhouse for this exercise. Ask the Greenhouse Supervisor or an AI for help.

a. Select a small leaf from an inconspicuous spot on the philodendron, spider plant, and impatiens.

b. Back at the lab, carefully tear the leaf to make a ragged edge to inspect under the microscope. The best tears show a clear layer of epidermis, a partial layer of the inner portion of the leaf, and an intact section of leaf.

c. For the philodendron, make two tears so that the upper surface and lower surface can be inspected.

d. Label 3 glass slides. Place your torn leaf pieces on a few drops of water on the slides and cover with a cover slip.

2. Things to do and questions to ponder

a. Inspect the impatiens leaf. Under low power, find the puzzle-shaped epidermal (outer layer) of cells on the lower surface of the leaf.

b. Do you see a bunch of dark dots scattered around? Center one of these dots in the field of view, and lswitch to high power. The dots are stomata, the openings in a leaf surface for gas exchange. The lstomata are surrounded by crecent shaped "guard cells" containing chloroplasts. When guard cells fill with water, they elongate and open the stomata. Cool, huh?

c. Inspect the philodendron leaf upper surface under low power. Do you see the distinct vascular system?

d. Compare the upper and lower epidermis of the philodendron. What very obvious difference do you see between the two surfaces?

e. Finally, compare the shape of the epidermal cells of the spider plant with those of the impatiens. How would you describe their shape? I'm thinking reptilian skin!

Beef it up!

You are what you eat, and you should know what that is.

1. Obtain a dime-sized (or smaller!) piece of hamburger (from Commons? But don't tell them who sent you!) Be sure to follow sanitary practices when handling raw meat: wash your hands in hot, soapy water immediately after handling the meat, and clean the area where you are working and utensils with soapy water.

2. Soak the hamburger in a little water for about 10 minutes to elute the blood.

3. Tease apart a tiny portion of the hamburger with a pin on a slide.

4. Place two drops of water on the slide. Squash an even smaller portion of burger under the cover slip. (This is not gross, it's science!)

5. Things to do and questions to ponder

a. Use medium power to find striated muscle fibers. This striped pattern is typical of skeletal muscle. Muscle fibers are usually very long, but these are not-the meat grinder chopped them up!

b. If you have inspected some plant cells, conjecture why plant cells tend to me much larger than animal cells (although not muscle cells!).

c. Skim an account of how muscle fibers contract-the Z lines get closer together!

Go with the Flow

Elodea is a common fresh water plant that may be available in the department. It certainly can be found at a pet supply shop, where it is sold for aquarium use.

1. You must use photosynthetically active leaves. Crank up photosynthesis by placing a length of plant (a 2 inch piece will suffice) in pond water under a desk lamp for 30 to 60 minutes.

2. Simply mount a whole leaf in water under a cover slip.

3. Things to do and questions to ponder

a. Under medium or high power, locates some cells in which the chloroplasts are streaming around the edge of the cells.

b. Elodea leaves are only a few cell layers deep. Use the fine focus to peer through the layers. Note that the cells are not superimposed over each other. What is their arrangement, and suggest why it is so?

c. Do you see any stomata (see the exercise, "Get Personal with a Plant," above)? Why not?

Created by Kathy Claerr 1-9-2003
Department of Biology
Bates College