Materials Included In Kit

Additional Materials Required

Prelab Preparation

The following are suggestions for setting up this activity.

• Use a small piece of paper and tape to cover all identifying labels on the prepared slides. Write a number on each slide.
• Set up microscopes with the lowest power objective in place then put the prepared slides on the stage.
• For Part A, additional microscopes should also be set up with a few crystals of salt or sugar sprinkled on blank slides. No cover slip is needed.

Safety Precautions

Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. All other laboratory safety rules should be observed.

Lab Hints

• Since making good drawings is one goal of this activity, only two students per microscope is recommended. This will help eliminate excessive talking and horseplay. The size estimation activity included will help keep students on task while waiting to view and draw the “mystery” slides.
• If additional wait time is needed, assign students to use the Internet or their textbooks to find 5–10 micrographs (pictures) of microscopic objects and print them, preferably in color. Cut out the pictures and make a small collage by gluing them to a sheet of blank paper. The micrographs should have a similar theme (i.e., insect parts, algae, protozoa). Above or below each micrograph, identify each micrograph and the magnification at which each was taken, if possible. This activity may also be assigned as homework and/or extra credit, if students have access to the Internet at home.
• Some suggested websites for finding micrographs are:

http://www.microimaging.ca/forum.htm (Accessed May 2018)
http://www.microscopy-uk.org.uk/mag/art98/milli.html (Accessed May 2018) With red and blue glasses, images are visible in 3-D on this website.

Teacher Tips

• Becoming good observers and being able to draw something that looks reasonably correct are important skills in microscopy.

• This activity can be done as a culminating review exercise upon completion of a microscopy unit.
• This activity has been purposely designed to allow teachers to mix up the numbers of the “mystery” slides for different classes and, if desired, incorporate or substitute other slides.

Sample Data

Student Drawings

The page of drawings is only to give a general idea of what students should be seeing and drawing when they view each slide. Obviously, student drawings will vary dramatically from these, depending on the time each student takes to make a good sketch and/or the patience of the student.

The slide identities are as follows:

Unknown #1—Yeast
Unknown #2—Volvox
Unknown #3—Planaria*
Unknown #4—Spirulina
Unknown #5—Turtle blood
Unknown #6—Sedum leaf epidermis
Unknown #7—Salt crystal
Unknown #8—Motor neuron
*Drawn using the low power (4X) objective; the others were drawn with the high power (40X) objective.

Calculations

Following is a sample completed data table using salt crystals.

Answers to Questions

1. What is the total magnification of an object if a microscope’s high power objective = 50X?

500X

2. What would be the estimated length of a rice grain if 2.5 grains were predicted to fit end-to-end across a field of view (FOV) of 4.5? (Record the answer in both mm and μm.)

3. Compare the size estimations of the crystals for each objective power.

1. How close to each other are the estimated sizes for each power?

   (Between .02 and .04 mm)

2. Which variable in the formula, d = D/X, has the most uncertainty when it comes to estimating the size of any microscopic object? Why?

   X is the most uncertain number because it is a guess as to how many objects fit across the diameter of a FOV.

4. List one thing that all eight objects on the slides have in common.

All the objects have distinct, definite shapes.

5. Which of the eight objects on the slides does not appear to have come from something living? How do you know? (List one supporting evidence.)

Salt crystals. The salt crystals did not appear to have anything inside of them. The other seven objects either had color or other structures inside of them.

References

Special thanks to Steve Parker of Gilman Public Schools in Gilman, WI, for sharing the idea for this activity with Flinn Scientific, Inc.

Introduction

This microscope activity will undoubtedly stimulate interest because it is “a small world, after all.” Use your powers of observation and artistic skills to make detailed pencil drawings match written descriptions.

Concepts

• Observation

• Basic microscopy usage
• Field of view
• Magnification

Background

One of the most important tools for studying the relationship between structure and function is the microscope. However, once an object is located and focused upon, identification is the next step. In some cases, identification is only possible when accurate descriptions, drawings and size estimations are made. Making detailed drawings through a microscope requires more patience than artistic ability and estimating the size of microscopic objects requires simple math calculations.

Experiment Overview

The primary objectives of this activity are to provide practice in locating and focusing upon objects within a microscope’s field of view, making drawings of microscopic objects with enough detail to correctly match a description and name and determining the approximate size of an object using a microscope.

Materials

Safety Precautions

The materials used in this lab activity are non-hazardous. Please follow normal safety guidelines, including proper handling, use and care of microscopes.

Procedure

Part A. Size Estimations

1. Several microscopes around the room contain slides with an unknown chemical in the form of loose crystals. Observe these crystals and estimate their size using each of the microscope’s objectives.
2. Calculate the size of the field of view (FOV) for each objective using the information in steps a and b and then record in the data table.

1. Divide each objective’s power by four. The number obtained is called the magnification factor (MF).
2. Divide the FOV diameter of the 4X objective, which is always 4.5 mm, by the MF of the objective to obtain the FOV for each objective.

Examples

An objective of 5X power—(a) divide 5/4 = 1.25 (MF), (b) divide 4.5 mm/1.25 = 3.6 mm, the FOV for 5X.

An objective of 3X power—(a) divide 3/4 = 0.75 (MF), (b) divide 4.5 mm/0.75 = 6 mm, the FOV for 3X.

The formula for estimating the size of objects under a microscope is: d = D/X where

d = size of the object (in mm)
D = diameter of an objective’s FOV
X =estimated number of objects that “fit” across the FOV diameter.

Example: D = 2 mm X = 60

Therefore d = 0.033 mm or 33 μm (microns)

A micron or micrometer is 1000X smaller than a millimeter (mm). An object with the size just calculated—33 μm—is about the size of a single human cheek cell.

3. Record all calculations and crystal size estimations in the data table. All size estimations must be in mm and μm.

Part B. “Mystery” Slides

1. Select one of the eight microscopes set up with a different prepared slide. (Only two students per microscope.)
2. Use the Microscope “Mystery” Worksheet to sketch the objects on each slide. Note: Increase the magnification as needed to clearly view any internal structures.
3. When the entire worksheet is finished, including the data table and Post-Lab Questions, request a Slide Description and Identification page from the instructor.
4. Use the numbers from each “mystery” slide and the written descriptions to identify each of the objects drawn. Note: Only use your diagrams for this part of the activity!
5. When finished, give the Slide Description and Identification page, along with the Microscope “Mystery” Worksheet to the instructor.

Student Worksheet PDF

10663_Student1.pdf