Download Prescott`s Microbiology, 9th Edition Chapter 25 –The Protists

Prescott’s Microbiology, 9th Edition
Chapter 25 –The Protists
GUIDELINES FOR ANSWERING THE MICRO INQUIRY QUESTIONS
Figure 25.4 How are these two protists morphologically similar but physiologically different?
Giardia and Trichomonas are both flagellated parasites. Giardia contains mitosomes which are
mitochondria-like organelles and are microaerophilic. Trichomonas does not require oxygen and
possesses hydrogenosomes rather than mitochondria.
Figure 25.5 What are the functions of the stigma and the reservoir?
In Euglena the stigma is a red eyespot that helps the organism orient to light. The reservoir
regulates the osmotic pressure within the organism.
Figure 25.8 How does a plasmodium differ from a single cell?
There can be as many as 10,000 synchronously dividing nuclei within a single plasmodium as
compared to a single cell. Also, plasmodia are diploid while single cells are haploid.
Figure 25.9 How would a mutant strain unable to secrete cAMP behave if mixed with a wild-type
strain? What if it were mixed with another cAMP mutant?
Mutants cannot secret cAMP (cannot release signal) but can detect the respond to the signal.
Thus, if mixed with the cAMP-releasing wild-type, they would behave normally and be included
in the aggregate. However, if only cAMP-deficient mutants were present, aggregation would not
be signaled.
Figure 25.13 What do you think is the function of the “sails” in Ornithocercus sp.?
The function of the sails in Ornithocercus is to allow it to catch tides and move through the
water.
Figure 25.15 What are the functions of the micronucleus and the macronucleus?
In Paramecium the micronucleus is diploid and divides by mitosis and transmits genetic
information through meiosis and sexual reproduction. The macronucleus are polyploidy and
divide by elongating and constricting, are involved in cell division, and are used as the source for
gene expression in cells.
Figure 25.20 How does the trigger for sexual reproduction (i.e., reduced size) compare with
more common stimuli that induce sexual reproduction? (Hint: Compare to radiolaria.)
In Radiolaria sexual reproduction is triggered by nutrient limitation or heavy feeding. In this case
two haploid nuclei fuse to form a diploid zygote encased as a cyst and the zygote is released
when nutrients are again available. In contrast, diatoms do not necessarily respond to
environmental factors, instead sexual reproduction ensues due to reduced size produced by many
cell divisions. Rapid division would be an indirect measure indicating an excess of nutrients.
Figure 25.23 Which of the cells shown above are haploid and which are diploid?
In Chlamydomonas reproduction, only the zygote is diploid (steps 4 & 5 in the illustration).
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