Chapter 12
Characterizing
and Classifying
Eukaryotes
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General Characteristics of Eukaryotic Organisms
• Five major groups
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Protozoa
Fungi
Algae
Water molds
Slime molds
• Include both human pathogens and
organisms vital for human life
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Protozoa
• Diverse group defined by three characteristics
– Eukaryotic
– Unicellular
– Lack a cell wall
• Motile by means of cilia, flagella, and/or
pseudopodia
– Except subgroup, apicomplexans
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Protozoa
• Distribution of Protozoa
– Require moist environments
– Most live in ponds, streams, lakes, and oceans
– Critical members of plankton
– Others live in moist soil, beach sand, and
decaying organic matter
– Very few are pathogens
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Protozoa
• Morphology of Protozoa
– Great morphologic diversity
– Some have two nuclei
– Macronucleus
– Contains many copies of the genome
– Micronucleus
– Variety in number and kinds of mitochondria
– Some have contractile vacuoles
– All produce trophozoites; some produce cysts
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Protozoa
• Nutrition of Protozoa
– Most are chemoheterotrophic
– Obtain nutrients by phagocytizing bacteria,
decaying organic matter, other protozoa, or the
tissues of host
– Few absorb nutrients from surrounding water
– Dinoflagellates and euglenoids are
photoautrophic
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Protozoa
• Reproduction in Protozoa
– Most reproduce asexually only
– Binary fission or schizogony
– Few also have sexual reproduction
– Some become gametocytes that fuse with one
another to form diploid zygotes
– Some utilize a process called conjugation
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Protozoa
• Classification of Protozoa
– Based on 18S rRNA and features visible by
electron microscopy
– One scheme classifies into six taxa
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Fungi
• Chemoheterotrophic
• Have cell walls typically composed of
chitin
• Do not perform photosynthesis
– Lack chlorophyll
• Related to animals
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Fungi
• The Significance of Fungi
– Decompose dead organisms and recycle their
nutrients
– Help plants absorb water and minerals
– Used for food and in manufacture of foods and
beverages
– Produce antibiotics
– Serve as important research tools
– 30% cause diseases of plants, animals, and humans
– Can spoil fruit, pickles, jams, and jellies
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Figure 12.15 Fungal morphology-overview
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Fungi
• Nutrition of Fungi
– Acquire nutrients by absorption
– Most are saprobes
– Haustoria allow some to derive nutrients from
living plants and animals
– May use ionizing radiation as energy source
– Most fungi are aerobic
– Many yeasts are facultative anaerobes
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Fungi
• Reproduction in Fungi
– All have some means of asexual reproduction
involving mitosis and cytokinesis
– Most also reproduce sexually
– Budding and asexual spore formation
– Yeasts bud in manner similar to prokaryotic
budding
– Pseudohypha
– Series of buds that remain attached to one
another and to parent cell
– Filamentous fungi produce lightweight spores that
disperse over large distances
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Figure 12.18 Representative asexual spores of molds-overview
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Fungi
• Classification of Fungi
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Division Zygomycota Division Ascomycota
Division Basidiomycota
Deuteromycetes
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Fungi
Division Zygomycota
• Most are saprobes.
• Form rough-walled sexual structures called
zygosporangia
• Microsporidia are zygomycetes that are
obligate intracellular parasites, some of
which are known to cause disease in
immunocompromised persons.
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Fungi
Division Ascomycota
• Form haploid ascospores within sacs
called asci.
• Ascomycetes include
– most of the fungi that spoil food, as well as
– plant pathogens - Dutch elm disease
– Many human pathogens( Aspegillosis in
humans and many others).
• Beneficial in baking and
brewing(Saccharomyces), research, and
pharmaceuticals (penicillium).
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Fungi
Division Basidiomycota
• Mushrooms and other fruiting bodies of
basidiomycetes, produce projections called
basidia, the ends of which produce sexual
basidiospores.
• Most basidiomycetes decompose cellulose
and lignin in dead plants and return
nutrients to the soil.
• Many produce hallucinatory chemicals or
toxins
• Cryptococcus neoformans – human
pathogen
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Fungi
Division Deuteromycetes
• The deuteromycetes, formerly classified
in the division Deuteromycota, are an
informal grouping of fungi having no known
sexual stage.
• Recently, the analysis of rRNA sequences
has revealed that most deuteromycetes
belong in the division Ascomycota,
• and thus modern taxonomists have
abandoned Deuteromycota as a formal
taxon.
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