Lab Topic 15
Diversity and Phylogenetic Trends Among the Protists
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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.
||(Class of 24 with 8 groups)
Oil immersion objectives (if possible)
Desk lamp with 60-watt bulb
Chlamydomonas, + and (CBS#15-1610)*
Termites infected with Trichonympha (CBS#13-1850)*
Diatomaceous earth (check local garden center)*
Prepared slides (can be shared by students to reduce costs)
Entamoeba histolytica (CBS#29-5474)*
Trypanosoma in blood smear (CBS#29-5816)*
Black paper, tape, and scissors
Slides, including depression slides
0.85% sterile saline
*Please refer to the Appendix for name and address of supplier.
About Three Weeks before Lab
Order slides and cultures as necessary to arrive week before lab.
Request pamphlets from supplier on handling algae and protozoan
Week before Lab
- Examine all materials for suitability as they arrive.
- Consider how room is to be organized for student access to materials
and prepare direction sheets for handling each culture.
- 0.85% sterile saline preparation:
0.85 g/100 ml water
Store in dropper bottles.
- 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.
- 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.
- It might be interesting to order some unknowns for the students
to examine and classify to phylum.
- Check out the links for this lab topic at http://auth.mhhe.com/biosci/genbio/dolphin/ You will find useful materials for developing your lab introduction
or summary, and in some cases, you may want to tell students to
connect to a particular site for further information.
ANSWERS TO CRITICAL THINKING QUESTIONS
- 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.
- 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.
- 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 shapeamoeboid,
4. Location of protist in the water columnis it planktonic? is
it found in the sediments?
- 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.
Algae, slide set. Omaha, NE: Nebraska Scientific. #S5-10560
Bio Sci II, videodisccontains photographic images of various protists. Dubuque,
IA: WCB/McGraw-Hill Publishers.
Diatoms, slide set. West Los Angeles, CA: Science Software Systems, Inc.
Protist, slide set. Rochester, NY: Wards. #170-W0078
Protozoa, 15-minute videocassette. Burlington, NC: Carolina Biological Supply.
Protozoans, slide set. Burlington, NC: REX Educational Resources.
A CD-ROM tutorial entitled Protista is available from CyberEd at http://www.cyber-ed.com/