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3 Domains are Archaea, Bacteria, and Eukarya. Eukarya has 4 kingdoms – Protista, Plantae, Fungi and
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.
1 Prokaryotes
1 prokaryotes
1 eukaryotes
2 No Histones
2 Histones
2 Histones
3 RNA polymerases- 3 types
3 several types
3 several types
4 introns absent
4 sometimes present
4 present
5 organelles absent
5 absent
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.
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.
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.
Forms: 3 main forms exist.
1 Bacillus - rod shaped bacteria, for example, Bacillus anthracis, causes anthrax
2 Coccus - spherical bacteria, for example, Streptococcus mutans, causes tooth decay
3 Spiral –slender spiral bodies, Trepanema pallidum, causes syphilis, a sexually transmitted disease.
Cell Structure: No nucleus is present. No Histone proteins associated with DNA. Ribosomes are smaller
than ribosomes of eukaryotes. All membrane bound organelles are absent. Flagella lack 9+2 arrangement
of microtubules found in eukaryotic cells.
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 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.
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 (100⁰C); Methanogens – these produce methane, the marsh gas as bye-product and
live in anaerobic marshes or digestive tracts of animals.
Protists were first eukaryotes to evolve. All eukaryotes lacking distinct characters of 3 higher kingdoms
are placed in kingdom Protista.
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.
Body Forms: Most are unicellular - Chlamydomonas, Euglena. Others are filamentous - Cells are placed
end to end to form a row = filament – Spirogyra. Colonial - many unicellular organisms live together in a
colony – Volvox.
• Body Coverings in Protista: Plasma membrane = cell membrane – Amoeba
• Pellicle: protein strips present below cell membrane and supported by microtubules, strips may
slide to form flexible covering (Euglena)
• Alveolate: alveoli are flattened sacs just below cell membrane – Ciliates-Paramecium,
dinoflagellates, sporozoans-malarial parasite.
• Cell wall outside cell membrane in green, brown and red algae
Nutrition in Protists: Like the 3 higher kingdoms the Protists are
Autotrophic - (plant like) – algae, dinoflagellates, diatoms have chlorophyll and make their own food.
Heterotrophic absorptive (fungus like) – Slime Molds are fungus like but can also eat food by
phagocytosis. Therefore, nutrition is termed Mixotrophic.
Heterotrophic Ingestive (animal like) – Amoeba, Paramecium and Trypanosoma take food inside and
digest it.
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 – Pyrrophyta 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 is Gonyaulax. The red tide is caused due to sudden growth due to availability
of Nitrogen or Phosphorus brought by rivers.
Red Algae - Rhodophyta 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 - Phaeophyta 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 brown alga, Sargassum. Algin a gelatinous material added to ice creams and cream
cheese is extracted from brown algae.
Euglenophyta 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
Ciliates include Protist moving 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 reproduction.
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.
Slime Molds are naked protists which feed by phagocytosis. Plasmodial Slime Molds have multinucleate
protoplasmic masses called plasmodium. These reproduce asexually by spores formed in walled
sporangia in a cluster called fruiting body. Spores develop into amoeboid or flagellated gametes.
Common example is Physarum species. Cellular Slime Molds 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.
Recap 1 Protists
1. Earth was formed --------- billion years ago.
2. Life originated on earth about ---- billion years ago
3. --------and-------organelles originated by endosymbiosis
4. Unicellular protist, autotroph, body covered with 2-piece silica shell, no flagella is -------------------5. Unicellular protist, autotroph, body covered with flexible pellicle, single flagellum is ----------------6. Unicellular protist, autotroph, body covered with cellulose plates, 2 flagella at 90⁰, is --------------7. Fungus like naked (no cell wall) protist, heterotroph, can eat by phagocytosis or by absorption is ----8. Animal like protist, has pseudopodia to locomote or feed is ----------------------FUNGI
These are multicellular, heterotrophic-absorptive eukaryotes. The fungus body is called Mycelium,
formed of many thread like Hyphae (singular is hypha).
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.
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 (singular ascus) which are enclosed in a
fruiting body called Ascocarp. Common examples are Yeasts, 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
basidiocarp. Basidiocarp bears gills on under surface. Gills have basidia. Common examples are
Mushrooms, puff-balls.
Fungi Imperfecti are mostly ascomycotes that have either lost sexual reproduction or it has not been
observed so far. Most reproduce asexually by Conidia. Common examples are Aspergillus and Penicillium.
Penicillium was the source of 1st commercial antibiotic drug Pencillin to cure bacterial diseases.
Recap 2 Fungi
1. ---------is fungal body formed of network of thread like structures ---------------.
2. Mycelium can have septa separating nuclei or ------------ having large # of nuclei with no septa in
3. -----------are oldest fungi; only group to have flagella in spores or male gametes.
4. ----------- are fungi that form thick walled zygotes called zygospores.
5. Truffels, Morels and Yeasts are examples of fungi ---------------.
6. Mushrooms and puffballs are example of fungi ------------.
7. In -------- ------------ sexual reproduction is either absent or not discovered so far.
8. Aspergillus and Penicillium belong to group -------------.
9. Bread mould Rhizopus belongs to fungal group -------------.
10. Cell wall in Fungi is made of -----