Microworlds is an eight-week, 16-lesson unit designed and tested for 5th grade but adaptable for use in 6th grade. The primary objectives of the unit are:

• For students to learn how to observe.
• For students to learn how to record their observations, using both writing and drawing.
• For students to learn about the properties of magnifiers.
• For students to become skilled at using hand lenses.
• For students to become skilled at using microscopes, slides, coverslips, droppers and other related apparatus.
• For students to observe a wide variety of specimens, both living and nonliving, under magnification.

The unit is composed of sequential phases that build upon one another. In the first phase, students make close observations of common objects--a penny, fabrics, screen wire, and pencil shavings. They record their observations, both by writing and drawing. These initial lessons can be used as a baseline from which the teacher can assess student progress.

In the second phase of the unit, students are introduced to different lenses--magnifying glasses, acrylic spheres, and water drops--and use them to discover that in order to magnify, an object must be transparent and curved. Students then are ready to meet the microscope, which is really just a set of lenses conveniently mounted for easy use.

In the third phase, students use the microscope to view inanimate objects. Much attention is paid to focusing and lighting techniques. Students begin by observing flat objects, such as microfiche, and newspaper and magazine photographs. They continue with hair from their head, and use it to measure specimens. They grapple with the concept of field of view and try to decide exactly how much of an object they can see under the microscope all at once. They learn through reading about two relevant historical figures, Anton Leeuwenhoek and Robert Hooke.

Students also learn to prepare slides of different types to suit different specimens. They experiment with flat slides and coverslips, tape as a coverslip, and well slides, to decide which is most appropriate in a given situation. In addition to specimens provided in the kit, there are built-in opportunities for students to explore objects they themselves bring in. As a culmination to this phase, students observe an onion from the outside in. They predict what they think they will see, make an observation, and then record what they do see. The observation proceeds from the outer skin to a longitudinal section to a cross section, and ends with an examination of cells on student-prepared slides.

In the last phase of the unit, students must use all of the expertise they have developed in order to successfully view their new specimens: living creatures. They also must learn some new techniques for preparing slides and for slowing the motion of the microscopic creatures, while keeping in mind that these creatures are, after all, alive.

Once again, students work from the easiest specimens to view to the most difficult. They begin with Volvox, which is a relatively large, bright-green alga. They should have little difficulty in locating it on a slide and tracking its slow, rolling progress. Next, they observe Blepharisma, which is bright pink and fairly large, but faster moving. Then the vinegar eel presents real challenges. Although it is the largest living organism to be viewed, the vinegar eel is transparent, very quick moving, and not particularly pleasing to look at.

The unit closes with observations centered on the hay and grass infusions set up earlier in the unit. Since it is impossible to predict what students will find in the infusions, these lessons are best approached with a spirit of adventure. The teacher may also use them to evaluate student progress.

A few words about the appendices.

• Appendix A is a series of post-unit assessments.
• Appendix B is a checklist for recording student progress.
• Appendix C is a mini-art lesson for classes having particular difficulty recording observations through drawing.
• Appendix D provides some materials for a bulletin board or learning center.
• Appendix E contains notes on the care and feeding of live cultures.
• Appendix F is a Bibliography of recommended books for students and teacher.

You do not have to be an expert in microbiology to teach this unit. The background sections of the Teacher’ Guide will provide you with most of the information you need. But don’t be surprised if you find yourself learning along with the students, and if you and your students find yourselves faced with puzzling questions. Use this situation to model the way scientists learn: define the question, then ask, "How can we find out?" This will encourage your students to find out on their own by experimenting and consulting resource materials.