ANSWERS TO REVIEW QUESTIONS – CHAPTER 35
1.
What major technological advances have allowed biologists to discover great diversity and
previously unrecognised evolutionary relationships in the protists? Why is the kingdom
Protista considered to be an artificial taxon? (p. 836)
New developments in biochemistry and molecular biology have permitted a better understanding of the
relationships between different protist groups. The kingdom Protista contains many diverse groups of
organisms, some of which are more closely related to other kingdoms than each other. While there are
still groups of unknown evolutionary affiliation, it is more convenient to retain the catch-all Protista.
2.
Make a table comparing the main distinguishing features of red, green and brown algae.
What useful substances are obtained from red, green and brown algae? (pp. 846–849)
Division/class
Main pigments
Main storage
products
Cell forms
Cell covering
Rhodophyta
(red algae)
chlorophyll a
phycocyanin
phycoerythrin
Floridean starch
unicellular,
filamentous, thalloid
Phaeophyceae
(brown algae)
chlorophyll a
chlorophyll c
fucoxanthin
chrysolaminarin
multicellular with
wide range of
morphologies
Chlorophyta
(green algae)
chlorophyll a
chlorophyll b
ß-carotene
lutein
zeaxanthin
starch
coccoid, unicellular
or colonial
flagellates,
multicellular or
multinucleate
filaments, complex
thalloid
cell wall of cellulose
or xylan fibrils in
mucilaginous matrix
which may contain
agar/carrageenan;
some calcified
cell wall of cellulose
fibrils in a
mucilaginous matrix;
stiffened by calcium
alginate
mainly cellulose, but
also polymers of
xylose or mannose
The red algae provide several useful products, including gelling agents such as agar and carrageenan,
and are also used as food, especially Porphyra (‘nori’ or ‘laver’). Some of the brown algae are farmed
for various chemicals, including soda, iodine and algin, a polysaccharide. They are also used for animal
food and fertiliser. Some of the green algae are cultured to extract pigments such as ß-carotene and
other chemicals.
3. (a) Why are the brown algae called heterokonts and what are their closest relatives? (p. 849)
The name Heterokontophyta describes the different morphology of the flagella in members of this
group: a long, hairy flagellum, directed forward, and a shorter, smooth flagellum which points
backwards along the cell.
(b) What are the closest relatives of the green algae? (pp. 847–849)
The green algae are believed to be most closely related to the higher land plants, which are believed to
have developed from the class Charophyceae.
4.
What features would enable you to identify a protist as (a) a euglenoid or (b) a
dinoflagellate? Describe how each of these protists moves and how they gain their nutrition.
(pp. 856–863)
Euglenoids differ from dinoflagellates in several aspects:
1.
2.
Euglenoid cells are surrounded by proteinaceous strips, wound around the cell, while
dinoflagellates are surrounded by a layer of flat vesicles which usually contain cellulose plates.
Euglenoids contain the primary pigments chlorophyll a and b, while dinoflagellates contain
chlorophyll a and c.
3.
4.
5.
6.
While euglenoids have paramylon as the main storage product, dinoflagellates have starch and
lipid.
Both dinoflagellates and euglenoids generally have two flagella, although their orientation and the
resulting swimming pattern are somewhat different. In the euglenoids one of the flagella is short
and does not usually emerge from the gullet, while the other, longer flagellum effectively pulls the
cell along. The proteinaceous plates slide over each other, and permit flexibility in the cell,
permitting the gyrating and crawling motion known as polymoby. In dinoflagellates, one of the
flagella emerges from the longitudinal groove, and is oriented in front of the cell, pulling it along,
while the other remains within the transverse (girdle) groove. This causes the cell to spin as it
swims.
About a third of euglenoids are photosynthetic, while the remainder are heterotrophic. Some of the
photosynthetic species are facultative heterotrophs, also able to engulf prey via the gullet. Some
species are parasitic.
Dinoflagellates also show a variety of nutritional modes. About half are photosynthetic, while
many are predatory, capturing their prey using specialised tentacles. The zooxanthellae are a
photosynthetic group that are endosymbionts with various invertebrate animals.
5. What are red tides? Why have they become a problem in Australia? (pp. 856–857)
Red tides refer to rapidly growing blooms of dinoflagellates, where the concentrations are so great that
the water appears red. Some red tides can cause fish kills, either through anoxia or by the release of
toxins; some of these toxins can be fatal to humans. Increased nutrient levels in coastal waters as a
result of land run-off, pollution and aquaculture has resulted in eutrophic conditions in some places.
Such conditions can produce algal blooms. The spread of toxic species by shipping has further
increased the likelihood of toxic algal blooms.
6.
What is unusual about the genetic material in ciliates? How do ciliates reproduce sexually?
(pp. 858–860)
Ciliates have two types of nucleus: a micronucleus, containing a ‘master copy’ of the genetic material,
and a macronucleus which contains the ‘working copy’. Messenger RNA is transcribed from the gene
copies in the macronucleus, but not the micronucleus copy, which is reserved for sexual reproduction.
Sexual reproduction is by conjugation: two cells of opposite mating type become attached, and genetic
material is exchanged. Fusion of the haploid micronuclei produces a new diploid micronucleus. The
macronuclei degenerate, and new macronuclei are produced from the recombinant micronuclei.
7.
What type of protist is a trypanosome? How do these parasites avoid being eliminated by
the immune system when they are in the bloodstream of their host? (pp. 861–863)
Trypanosomes are parasitic flagellates that are free-swimming in the blood of vertebrates, including
humans. These protists cause a number of significant diseases, including African sleeping sickness and
Chagas’ disease. They can remain in the host’s blood stream by constantly changing their surface
glycoprotein layer, thereby evading ‘detection’ by the host’s immune system.
8.
What groups of protists belong to the alveolates and what characteristics do they have in
common? (p. 856)
Dinoflagellates, apicomplexans and ciliates. They all have cortical alveoli beneath the plasma
membrane.
9. What is the apical complex? Which protists possess one? What does it do? (p. 858)
The apicomplexans are those parasitic protists that possess an apical complex, which is a structure
comprised of microtubules and secretory vesicles, used to penetrate a host cell.
10. What is the difference between cellular slime moulds and plasmodial slime moulds?
Cellular slime moulds are colonies of small amoeba, whereas plasmodial slime moulds consist of one
large multinucleate cell. (pp. 841–842)