Download DOMAINS AND KINGDOMS – Chapter 16-17

DOMAINS AND KINGDOMS – Chapter 16-17
Archaea, Bacteria, Eukarya – Protista, including Algae, and Fungi
Carl Woese based on studies of r-RNA in various groups of living things suggested 3 Domain
classification. The arrangement of nucleotides is highly conserved because the mutation rate in
r-RNA is very slow.
BACTERIA
1 Prokaryotes
2 No Histones
3 RNA polymerases- 3 types
4 introns absent
5 organelles absent
ARCHAEA
1 prokaryotes
2 Histones
3 several types
4 sometimes present
5 absent
EUKARYA
1 eukaryotes
2 Histones
3 several types
4 present
5 present
Viruses, Viroids and Prions:
All are acellular infectious agents much smaller than bacteria.
Viruses have a genome of RNA or DNA ( single stranded or double stranded) covered by a layer
of proteins called Capsid. In animal viruses, the Capsid is further covered by the host membrane
studded with viral spikes. This covering is called Envelope. Diseases: Measles, AIDS, Common
Cold and Flu etc. Fig 17.6
Viroids lack capsid. They are formed of only RNA. They infect only plant cells.
Prions are formed only of proteins. They are rogue misfolded proteins causing normal proteins
to change to infectious form. These cause degenerative diseases of brain. Diseases—mad cow
disease, Creutzfeld-Jacob disease etc.
BACTERIA:
Cell Wall: contains Peptidoglycan. It can get stained with crystal violet-Iodine. If the bacteria
retain the stain on washing-these are called Gram+. If the stain is washed, the bacteria are stained
with Safranin. These are called Gram- bacteria and have a second membrane outside cell wall.
Fig 17.3
Forms: 3 main forms exist.
1 Bacillus - rod shaped bacteria
2 Coccus - spherical bacteria
3 Spiral or Curved bacteria
Cell Structure: No nucleus. No histones associated with DNA. Ribosomes are smaller than
ribosomes of eukaryotes. All membrane bound organelles are absent. Flagella lack 9+2
arrangement.
Metabolism: Most bacteria like animals require organic molecules. These are saprobes and
release enzymes to absorb food from outside. Besides fungi these are the main decomposers.
Cyanobacteria have Chlorophyll a for photosynthesis like algae and plants (oxygenic
photosynthesis). Others use hydrogen sulfide instead of water and release sulfur instead of
oxygen (anoxygenic photosynthesis). Still others can gain electrons from inorganic chemicals to
reduce CO2 (Chemosynthesis). Cyanobacteria have Chlorophyll a and other pigments in
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thylakoids. Some have only photosynthetic cells like Oscillatoria species and others in addition to
photosynthetic cells have Heterocysts are specialized for Nitrogen Fixation, like Nostoc.
Reproduction: All reproduce by Binary Fission. DNA is replicated and 2 daughter chromosomes
move apart followed by division of cell by plate method. Some bacteria produce Endospores
which can tolerate extreme harsh conditions. Examples are Anthrax and Tetanus bacteria.
Some bacteria are branched and are best sources of Antibiotic Drugs which kill pathogenic
bacteria. Example is Streptomyces bacteria. Antibiotic drugs inhibit protein synthesis in bacteria.
ARCHAEA:
These prokaryotic organisms of ancient origin live in extreme environment. They share many
characteristics, like histones associated with DNA, with eukaryotic organisms. These include
extreme Halophiles – these can tolerate very high concentrations of salts; Thermophiles – these
can tolerate very high temperatures (100C); Methanogens – these produce methane, the marsh gas
as bye-product and live in anaerobic marshes or digestive tracts of animals.
Protists
Protists were first eukaryotes to evolve. All eukaryotes lacking distinct characters of 3 higher
kingdoms are placed in kingdom Protista Most are unicellular. Others are filamentous or colonial.
Mitosis, Meiosis and sexual reproduction arose for the first time in this kingdom. All the
organelles of plants, fungi and animals arose in this kingdom. The protists also possess many
unique organelles not found anywhere else in the 3 domains. Like the 3 higher kingdoms the
protists are photosynthetic (like plants) or heterotrophic absorptive (like fungi) or heterotrophic
ingestive (like animals).
Table 17.2 shows the many kinds of protists and is useful to compare important characters of each
group.
Algae are now part of kingdom protista. All have Cholorophyl a, and some additional pigments.
The chloroplasts in Algae have special organelle, Pyrenoid, to store and metabolize starch.
Asexual reproduction can be by flagellated spores called zoospores or spores without flagella.
Sexual reproduction is by flagellated gametes. Many algae, like plants, form a non-flagellated egg
and a flagellated sperm. This sexual reproduction is called Oogamy. Algae lack multicellular sex
organs.
Green Algae are most common in fresh water. These have Chlorophyll a and b, store food as
starch and have cellulose in cell walls. All characteristics are common with plants. But lack
multicellular sex organs covered with sterile jackets and embryos. They have various forms:
unicellular-Chlamydomonas; filamentous-Spirogyra; leafy - Ulva or colonial - Volvox with
daughter colonies inside.
Diatoms are most abundant unicellular forms in oceans. The body is covered with an intricately
designed 2-half silica shell. Adults are Diploid and lack cilia or flagella. Main reproduction is by
binary fission. Sexual reproduction is by flagellated gametes. The remains of shells produce
Diatomaceous earth mined for filtering and abrasive materials. Diatoms are most important
producers in biosphere.
Dinoflagellates are unicellular covered with cellulose plates. They have 2 flagella placed at right
angle to each other. These are important phytoplanktons in oceans. They are also responsible for
causing Red Tides, example Gonyaulax. The red tide is caused due to sudden growth due to
availability of Nitrogen or Phosphorus brought by rivers.
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Red Algae are important sources of gelling agents Agar and Carageenan. Porphyra is edible red
alga used as a sushi-wrap. These are mainly filamentous or leafy. Besides Chlorophyll a, these
have red and blue pigments to give various colors. Red algae are delicate sea weeds.
Brown Algae are usually the large sea weeds called Kelps. In addition to Chl a, these have
fucoxanthin a brown pigment. Coastal areas have Laminaria and giant marine kelp Macrocystis.
Sargasso Sea has floating red algae. Algin a gelatinous material added to ice creams and cream
cheese is extracted from brown algae.
Euglenoids are unicellular freshwater forms. Many have choloroplasts others lack them. The
chloroplasts are surrounded by 3 membranes than the normal 2. The anterior end has vase-like
invagination. Out of which emerges a long flagellum, the other is small. Eye-spot is sensitive to
detect light. The body is covered by Pellicle formed of protein strips. They can change body
shape. A contractile vacuole lies near the anterior end. Reproduction is by longitudinal cell
division. Sexual rep is absent.
Protozoan Protists
These are animal-like-protists. They are motile and heterotrophic ingestive portists. There are 4
main types:
Ciliates include protists locomoting with cilia and covered with pellicle. Common example is
Paramecium species. It has a Meganucleus and a Micronucleus. These reproduce asexually by
transverse cell division. Sexual rep is by Conjugation for which 2 paramecia join temporarily and
exchange nuclei and separate. 2 nuclei from different paramecia fuse to result in fertilization.
They have 2 contractile vacuoles surrounded by feeding canals. They lack sexual rep.
Amoeboids are covered with cell membrane only and locomote by pseudopodia which are
formed by flowing cytoplasm. They change, all the time, their body-shape. They feed by
phagocytosis. Freshwater forms have contractile vacuoles to expel excess water. Common
example is Amoeba proteus. Entamoeba causes dysentery-blood in stools and gingiva-soft
bleeding gums. Foraminifera are amoeboids covered with lime-shells called tests with many
pores. Radiolarians have internal silica test. The shells of the 2 groups deposit as sedimentary
rocks at sea bottom.
Zooflagellates locomote with flagella and body is covered by plasma membrane. Most are
symbionts and help in digestion of cellulose (stomach of ruminant mammals). Others are
parasites and cause diseases. Common example is Trypanosoma which lives in blood plasma of
humans and causes sleeping sickness in Africa. It is transmitted by Tse-tse fly.
Sporozoans are without any locomotory organelle. At one end of the cell is apical complex. It
helps in entry into host. Common example is Plasmodium species which causes Malaria. It is
transmitted by females of mosquito, Anopheles species. Malarial parasite completes sexual phase
in Anopheles and asexual reproduction in human liver and red blood cells.
Molds as Protists: These are fungus-like-protists. They have flagellated cells. 2 types:
Water Molds are filamentous and their cell walls are mainly formed from cellulose. Asexual
reproduction is by flagellated spores. Sexual rep is by oogamy- an egg and sperm. Common
example is Phytophthora which causes potato blight. It caused the Irish famine in 1940.
Slime Molds are naked protists which feed by phagotysis. Slime Molds may be multinucleate
protoplasmic masses called plasmodium. These are called acellular slime molds. These reproduce
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asexually by spores formed in walled sporangia in a cluster called fruiting body. Spores develop
into amoeboid or flagellated gametes. Life cycle is shown in fig 28.22. Common example is
Physarum species. Other slime molds are cellular and live as solitary amoeboid cells. Under
unfavorable conditions these can form aggregations called pseudoplasmodium. When favorable
conditions return sporangia in a fruiting body produce spores. The spores give rise to single cells
to complete the cycle.
FUNGI
Fungi typically lack flagellated cells. Only exception is Chytrids which have flagellated spores.
These are multicellular, heterotrophic-absorptive eukaryotes. The fungus body is called
Mycelium, formed of many thread like Hyphae.
Zygospore Fungi-Zygomycota are molds with non-septate hyphae. These reproduce asexually
by spores. The gametes formed at the tips of special hyphae, fuse to form zygospore, a thick
walled zygote. Under favorable conditions zygospore undergoes meiosis and forms spores which
produce the mold again. Table 17.3. Common example is Rhizopus the black bread mold.
Sac fungi - Ascomycota have septate hyphae. Most of them reproduce asexually by conidia.
Conidia are formed in chains by budding. Two hyphae of + and – strains fuse. The resulting
hyphae have 2 nuclei in each cell. Fusion takes place in a special structure called Asci which are
enclosed in a fruiting body called Ascocarp. Common examples are Morels and Truffles.
Club Fungi- Basidiomycota has special bodies called basidia. Fusion of nuclei take place in it
and 4 sexual spores are formed externally from each basidium. Spores germinate to form
monokaryotic mycelium. The tips of + and – strains of hyphae fuse to form dikaryotic hyphae
which form the fruiting body called Ascocarp. Ascocarp bears gills on its under surface. Gills
have basidia. Table 17.3 Common examples are Mushrooms, puff-balls.
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