Bauman Chapter 12 Answers to Critical Thinking Questions
p. 355
In Chapter 4 (see p. 121), we discussed identifying microbes using dichotomous
taxonomic keys. Design a key for the genera of protozoa discussed in this section.
* Note that the chapter does not provide information on which to base a dichotomy for
the three neurotoxic dinoflagellates.
Yes
Alveoli
present?
See next page
Cilia?
No
Yes
Photosynthetic?
Apical band
of cilia?
Yes
No
Yes
Midline band
of cilia?
Yes
No
No
Didinium
Neurotoxic?
Paramecium
Insect host?
Yes
Free-living?
Yes
No
No
Gymnodinium
Gonyaulax or
Pfiesteria *
No
Toxoplasma
Balantidium
Yes
Vorticella
Tick?
Yes
Babesia
No
Plasmodium
Mitochondria
present?
Yes
Photosynthetic?
Yes
No
Flagella?
No
Yes
No
Free-living?
2 nuclei?
Euglena
Trypanosoma
Yes
Yes
No
No
Entamoeba
Shell?
No
Polar
filament?
Yes
Yes
No
Insect host?
Yes
Insect
host?
Acanthamoeba
Silica?
Giardia
No
No
No
Nosemia
Yes
Yes
Foraminifera
Microsporidium
Radiolaria
Trychonympha
Trichomonas
p. 359
Fungi tend to reproduce sexually when nutrients are limited or other conditions are
unfavorable, but reproduce asexually when conditions are more ideal. Why is this a
successful strategy?
Sexual reproduction increases genetic variation, increasing the odds of some progeny
being well suited to new or challenging conditions (limited nutrients, etc.). When
conditions are favorable and a genotype is successful, creating new genetic
combinations is unnecessary and wasteful of energy. (Don’t mess with success.)
p. 371
Why are cellular slime molds called “cellular”?
Cellular slime molds have a single nucleus in each cell, and do not form a true syncytium
or coenocyte.
p. 366
Design a key for the genera of fungi discussed in this section.
Reproduce
sexually?
Yes
No
Dimorphic?
Zygospores?
Yes
Yes
No
No
Histoplasma
Rhizopus
Ascospores?
Trichophyton
No
Yes
Monomorphic
yeast?
Monomorphic
yeast?
No
Yes
No
Plant pathogen?
Poisonous?
Pathogenic?
Yes
Yes
No
No
Yes
Amanita
a
Claviceps
Saccharomyces
Yes
Coccidioides
Tuber
No
Agaricus
Cortinellis
Mycorrhizae?
No
Yes
Penicillium
Penicillin?
No
Neurospora
p. 367
Since Prototheca is colorless, how do scientists know that it is really a green alga?
Scientists know that Prototheca is a green alga based on the presence of genetic
sequences common to the green algae.
p. 369
Design a key for the genera of algae discussed in this section.
* Note that the chapter does not provide information on which to base a dichotomy for
the three neurotoxic dinoflagellates.
Cell wall?
Yes
No
Chrysolaminarin?
Euglena
No
Yes
Cellulose?
Navicula
No
Yes
Yes
Agar?
Laminarin?
Yes
No
Macrocystis
No
Gelidium
Chondrus
Histones?
Yes
Yes
Colorless?
No
Dinoflagellates
(see comment
above *)
No
Crosswalls?
Prototheca
Yes
No
Helical chloroplast?
Yes
Spirogyra
Codium
No
Trebouxia
p. 375
1. How are cysts of protozoa similar to bacterial endospores? How are they different?
Cysts of protozoa are metabolically inactive and resistant to drying and some
disinfectants, similar to bacterial endospores, but protozoal cysts are not as resistant as
endospores to heat treatment and irradiation, and do not survive as long. Further,
protozoan cysts are eukaryotic; whereas, bacterial endospores are prokaryotic.
2.
The host of a home improvement show suggests periodically emptying a package of
yeast into a drain leading to a septic tank. Explain why this would be beneficial.
Saccharymyces (household yeast) is a metabolically versatile organism that can
catabolize biomolecules completely in the presence of oxygen, and in the absence of
oxygen can convert metabolic intermediates to useful substrates. Yeast can both
participate in the breakdown of sewage wastes, and contribute to the establishment of a
diverse microbial community that can effectively recycle the materials in the septic tank.
3.
Why doesn’t penicillin act against any of the pathogens discussed in this chapter?
Penicillin interferes with the synthesis of peptidoglycan cell walls, a structural feature of
most bacteria that is not present in eukaryotes.
4.
How can one distinguish between a filamentous fungus and a colorless alga?
Fungi produce cell walls made of chitin, while algae do not have chitin. The fungi share
genetic sequences with animals, while algae are related closely to plants.
5.
Why do scientists as a group spend more time and money studying protozoa than
they do studying algae?
Protozoa are highly diverse in their metabolism, structures, etc., so they are very
interesting to study. Some protozoa cause disease, while algae are largely beneficial
and not harmful. More money is available to study organisms that cause disease
(troublemakers are often more interesting).
6.
Why are there more antibacterial drugs than antifungal drugs?
Fungi are eukaryotes and have metabolisms similar to that of humans, whereas bacteria
have more significant differences in structure and metabolism. As a consequence, it is
much easier to find chemicals that are toxic to bacteria but not to humans than it is to
find chemicals toxic to fungi but harmless to humans.