Exercise 15 - Protists

Students examine live cultures and prepared slides of protists. Theories on the evolutionary development of multicellularity are illustrated by looking at selected examples of algae. Several parasitic protozoans are also examined. Economically important protistans are discussed.

EQUIPMENT	AMOUNT (Class of 24 with 8 groups)
Compound microscope	1/student
Oil immersion objectives (if possible)	1/student
Dissecting microscope	1/student
Desk lamp with 60-watt bulb	1/group

MATERIALS

PREPARATIONS

About Three Weeks before Lab

1. Order slides and cultures as necessary to arrive week before lab. Request pamphlets from supplier on handling algae and protozoan cultures.

Week before Lab

1. Examine all materials for suitability as they arrive.

2. Consider how room is to be organized for student access to materials and prepare direction sheets for handling each culture.

3. 0.85% sterile saline preparation:
   0.85 g/100 ml water

   Store in dropper bottles.

CLASSROOM SUGGESTIONS

1. It is not necessary to have a prepared microscope slide of each specimen for each student. Students can share slides as they work through the exercise delaying a particular observation until a slide is available. Suggest that at least one slide be available for every three students.

2. A kodachrome slide show on the diversity of protists can be assembled with slides from various sources. This can be put in a rear projection, automatic projector (Caramate) in a hallway cabinet for continuous viewing before and after labs. If your library has a media center, a slide-tape show can be made and placed on reserve.

3. It might be interesting to order some unknowns for the students to examine and classify to phylum.

ANSWERS TO CRITICAL THINKING QUESTIONS

1. Refer to Ex. 14 and 15. Include sexual reproduction producing zygotes that may encyst and enter dormancy, amoeba trophozoite cysts, pellicles, silica theca, cellulose theca, etc. of Protists. Compare to bacterial spores and capsules, mutation rates and DNA repair mechanisms, short reproduction time, etc.; and the heterocyst and akinete production, and gelatinous capsule of cyanobacteria.

2. Diatomaceous earth is composed of the silica shells of diatoms and is very abrasive (due to the sharp silica thecae). Animals such as slugs, snails and caterpillars that move along on surface of the soil would be deterred, if not destroyed, by the abrasive particles. As well, ingestion of soils or plant leaves treated with diatomaceous earth would probably destroy the gut.

3. Points to consider--
   1. Surface area to volume ratio
   2. Torpedo shape and ease of movement through water
   3. Support offered by water and its affect on shape--amoeboid, filamentous, etc.
   4. Location of protist in the water column--is it planktonic? is it found in the sediments?

4. Colonial cells may have produced a division of labor and cellular specialization. There may have been an increase in interdependency. A cell "losing" its flagella may perform a function other than locomotion. Sex cells may become separate from vegetative cells. Consider cooperation and specialization seen in Volvox, whereas the single-celled protists such as Euglenophyta and Ciliophora must perform many functions.

SUPPLEMENTAL MATERIALS

Algae, slide set. Omaha, NE: Nebraska Scientific. #S5-10560
Bio Sci II, videodisc--contains photographic images of various protists. Dubuque, IA: Wm. C. Brown Publishers. See appendix.
Diatoms, slide set. West Los Angeles, CA: Science Software Systems, Inc. #520-1360
Protist, slide set. Rochester, NY: Ward's. #170-W0078
Protozoa, 15-minute videocassette. Burlington, NC: Carolina Biological Supply. #49-8290
Protozoans, slide set. Burlington, NC: REX Educational Resources.