Complete Notes
The oldest classification of organisms was non-scientific, based on uses:
The Two Kingdom System was given by Linnaeus — organisms were classified into:
| Kingdom | Examples |
|---|---|
| Plantae | Chlamydomonas, Eubacteria, Chlorella, Fungi, Algae, Bryophytes, Pteridophytes, Gymnosperms, Angiosperms |
| Animalia | Amoeba, Paramecium, Earthworm, Insects, Monkey, Human |
Therefore, there was a need for more systems with better criteria.
The Five Kingdom System was given by R. H. Whittaker (1969). It uses the following main criteria:
| Kingdom | Cell Type | Cell Wall | Nutrition | Examples |
|---|---|---|---|---|
| Monera | Unicellular, Prokaryotic | Present, made of peptidoglycan (protein + sugar) | Mostly heterotrophic, some autotrophic | Bacteria, Cyanobacteria (BGA) |
| Protista | Unicellular, Eukaryotic | Cell wall may be present or absent | Both Autotrophic and Heterotrophic (mixotrophic) | Chlamydomonas, Amoeba, Paramecium |
| Fungi | Mostly multicellular, Eukaryotic | Present, made of Chitin | Heterotrophic (saprophytic/parasitic) | Yeast, Mushroom, Penicillium |
| Plantae | Multicellular, Eukaryotic | Present, made of Cellulose | Autotrophic (photosynthetic) | Algae, Bryophytes, Pteridophytes, Gymnosperms, Angiosperms |
| Animalia | Multicellular, Eukaryotic | Absent | Heterotrophic (ingest then digest) | All animals |
The Six Kingdom System (Domain System) was given by Carl Woese:
Bacteria are the sole members of Kingdom Monera. They are Cosmopolitan — present everywhere. In fact, a handful of soil can contain hundreds of bacteria.
Archaebacteria are extremophiles — they can live in extreme harsh habitats:
| Type | Habitat |
|---|---|
| Thermoacidophiles | Live in hot, acidic environments |
| Halophiles | Salt-loving bacteria |
| Methanogens | Live in marshy areas (O₂ absent); also found in the gut of ruminants — produce methane, used in making Biogas (Gobar gas) from cattle dung |
Eubacteria have a characteristic cell wall and may have flagella (if motile).
| Use | Example / Detail |
|---|---|
| Curd formation | LAB (Lactic Acid Bacteria) — e.g. Lactobacillus |
| Antibiotic formation | Streptomycin, Neomycin — from Streptomyces species |
| Nitrogen fixation (N₂) | Some bacteria fix N₂ inside root nodules of legume plants like Pea, Bean |
| Decomposition | Bacteria convert organic matter on dead/decaying material into simpler substances — perform decomposition |
| Disease | Causal Bacteria |
|---|---|
| Cholera | Vibrio cholerae |
| Typhoid | Salmonella typhi |
| Citrus Canker | Xanthomonas citri |
| Tetanus | Clostridium tetani |
Kingdom Protista was introduced by Haeckel, before Kingdom Monera was introduced. It contains unicellular eukaryotic organisms with a well-defined nucleus and membrane-bound organelles.
| Group | Examples / Features |
|---|---|
| Chrysophytes | Includes Diatoms and Desmids — golden algae, found in fresh water and marine habitats. Cell wall present, made of two halves (Epitheca and Hypotheca) that fit together like a soap box, with deposition of silica (siliceous shells) — cell walls are indestructible. Diatoms are the major producers in oceans, and their cell wall deposits accumulate at the ocean floor over time. |
| Dinoflagellates | Mostly marine and photosynthetic. Cell wall has stiff cellulose plates on the outer surface, with two flagella (one longitudinal, one transverse), present in furrows/grooves. They show various colours — yellow, green, brown, blue, red — depending on the main pigments present (e.g. Chlorophyll a/c, Carotenoids, Fucoxanthin, Phycocyanin, Phycoerythrin). Rapid multiplication of red-pigmented dinoflagellates (e.g. Gonyaulax) causes "Red Tide" — secretes toxins like Saxitoxin which can kill fish and other marine organisms. |
| Euglenoids | Mostly found in fresh/stagnant water. Cell wall absent — instead, they have a protein-rich layer called pellicle, which makes the cell flexible. Have two flagella (one long, one short). They are mixotrophic — behave like autotrophs (photosynthetic, contain chlorophyll) in sunlight, and like heterotrophs (predatory) in absence of light. e.g. Euglena. |
| Slime Moulds | Saprophytic protists. The body moves and grows on decaying twigs and leaves, forming an aggregation that can be visible to the naked eye. Under unfavourable conditions, the slime mould differentiates and forms fruiting bodies bearing spores at their tips — these spores have true walls that are resistant, and are dispersed to form new slime moulds. |
| Protozoans | Primitive relatives of animals (animal-like protists), considered ancestral to animals. Heterotrophic (predatory or parasitic). Includes: Amoeboid (e.g. Amoeba, Entamoeba — causes Dysentery, an intestinal issue), Flagellated (e.g. Trypanosoma), Ciliated (e.g. Paramecium — moves via cilia), and Sporozoans (spore-like, e.g. Plasmodium — causes Malaria). |
Members of Kingdom Fungi are mostly multicellular (except yeast, which is unicellular) and filamentous. They are Eukaryotes. Cell wall is made of Chitin + Glucan.
| Mode | Description |
|---|---|
| Saprophytic | Grow on dead organic matter and decaying material. |
| Parasitic | Take nutrition from a living host body. |
| Symbiotic | Live in mutually beneficial relationships. e.g. Lichen (with algae), Mycorrhiza (with plant roots). |
| Fungus | Significance |
|---|---|
| Penicillium notatum | Source of Penicillin — the first antibiotic discovered |
| Albugo candida | Obligate parasite causing white rust disease on Mustard plant |
| Puccinia graminis | Causes Black Rust on wheat — parasitic on different plants and animals |
Fungi are Cosmopolitan — found everywhere — in air, soil, water, on plants and animals. They grow efficiently and show great morphological diversity in warm, humid, moist/damp conditions; they grow less in cold (e.g. in refrigerators).
The body of most fungi is made of long, filamentous structures called Hyphae. The network of hyphae is called the Mycelium.
A Lichen is a symbiotic association between Fungi (called Mycobiont) and Algae (called Phycobiont).
Mycorrhiza is a symbiotic association between Fungi and the roots of higher plants. The fungus increases the surface area of roots for absorption of water and minerals (especially Phosphorus), and also protects roots from pathogens.
The term "virus" comes from "venum vivum fluidum", meaning "poisonous fluid".
| Property | Detail |
|---|---|
| Size | 0.02 - 0.2 μm — much smaller than bacteria (compared to bacteria: 1-2 μm) |
| Nature | Inert/inactive (acellular) when outside a host cell. They have no protoplasm or independent metabolism. Once they infect a living cell, they take over the host's cellular machinery to make more copies of themselves, which spreads the infection. |
| Capsid | Outer protein coat surrounding the nucleic acid — made of many small subunits called Capsomeres |
| Genetic Material | A virus can have either DNA or RNA as its genetic material (never both). |
| Virus Type | Genetic Material |
|---|---|
| Bacteriophages (infecting bacteria) | Mostly double-stranded DNA (dsDNA) |
| Plant Viruses | Mostly single-stranded RNA (ssRNA), some double-stranded RNA (dsRNA) |
| Animal Viruses | Can have ssRNA, dsRNA, or DNA — e.g. HIV (RNA virus), Mumps, Measles, Influenza, Polio viruses (RNA viruses) |
Q1. Which scientist introduced the Five Kingdom System of classification, and in which year?
(a) Linnaeus, 1758 (b) Haeckel, 1866 (c) R. H. Whittaker, 1969 (d) Carl Woese, 1977
Answer: (c) R. H. Whittaker, 1969
Explanation: R. H. Whittaker proposed the Five Kingdom System in 1969, classifying organisms into Monera, Protista, Fungi, Plantae, and Animalia, based on criteria like cell structure (prokaryotic/eukaryotic), body organisation, mode of nutrition, phylogenetic relationships, and mode of reproduction. Linnaeus gave the earlier Two Kingdom System (Plantae and Animalia), Haeckel introduced Kingdom Protista, and Carl Woese later proposed the Six Kingdom (Domain) System.
Q2. Heterocysts in Cyanobacteria like Nostoc and Anabaena are specialised for which function?
(a) Photosynthesis only (b) Nitrogen fixation, protected from oxygen (c) Reproduction by binary fission (d) Storage of starch
Answer: (b) Nitrogen fixation, protected from oxygen
Explanation: Heterocysts are specialised cells in certain cyanobacteria (e.g. Nostoc, Anabaena) that have thick walls preventing the entry of oxygen. Since the enzyme nitrogenase (responsible for nitrogen fixation) is highly sensitive to oxygen and gets inactivated in its presence, heterocysts provide an oxygen-free environment, allowing these cyanobacteria to fix atmospheric nitrogen (N₂) into usable forms.
Q3. Mycoplasma (PPLO) differs from typical bacteria in which key feature, making it pleomorphic?
(a) Presence of a thick peptidoglycan cell wall (b) Complete absence of cell wall (c) Presence of chitin cell wall (d) Presence of a nuclear membrane
Answer: (b) Complete absence of cell wall
Explanation: Mycoplasma (also called PPLO — Pleuro Pneumonia Like Organisms) is the smallest known living cell, about 0.3 μm in size, and completely lacks a cell wall. Due to the absence of a rigid cell wall, mycoplasma can take on various shapes, a condition called "pleomorphic". Many mycoplasma species are pathogenic and cause diseases in plants such as little leaf of brinjal and phyllody.
Q4. In the reproduction of fungi, what is the correct sequence of events during sexual reproduction?
(a) Karyogamy → Plasmogamy → Meiosis
(b) Plasmogamy → Karyogamy → Meiosis
(c) Meiosis → Plasmogamy → Karyogamy
(d) Plasmogamy → Meiosis → Karyogamy
Answer: (b) Plasmogamy → Karyogamy → Meiosis
Explanation: Sexual reproduction in fungi involves three sequential steps. First, Plasmogamy occurs — the fusion of protoplasm of two motile or non-motile gametes. This is followed by Karyogamy — fusion of the two nuclei. Finally, Meiosis (reductional division) occurs to restore the haploid number, producing haploid spores. In Ascomycetes and Basidiomycetes, there can be a delay between plasmogamy and karyogamy, during which the cell exists in a dikaryotic (n+n) stage.
Q5. Lichens are used as pollution indicators because they are highly sensitive to which pollutant?
(a) Carbon dioxide (CO₂) (b) Sulphur dioxide (SO₂) (c) Methane (CH₄) (d) Ozone (O₃)
Answer: (b) Sulphur dioxide (SO₂)
Explanation: A lichen is a symbiotic association between a fungus (mycobiont) and an alga (phycobiont), where the alga provides food via photosynthesis and the fungus provides shelter, absorbs water/minerals, and increases surface area. Lichens are extremely sensitive to sulphur dioxide (SO₂) pollution and fail to grow or survive in polluted areas with high SO₂ levels, which is why their presence or absence is used as a bioindicator of air pollution.
Q6. Which of the following is the key structural difference between a Virus and a Viroid?
(a) A virus has both DNA and RNA, while a viroid has neither
(b) A virus has a protein capsid around its nucleic acid, while a viroid lacks a protein coat and consists of free RNA only
(c) A virus is larger than a bacterium, while a viroid is smaller than a virus but has a thick cell wall
(d) A virus can reproduce independently, while a viroid cannot infect any host
Answer: (b) A virus has a protein capsid around its nucleic acid, while a viroid lacks a protein coat and consists of free RNA only
Explanation: A virus consists of genetic material (either DNA or RNA, never both) enclosed within a protective protein coat called the capsid, made up of subunits called capsomeres. A viroid, discovered by T. O. Diener (1971) as the cause of Potato Spindle Tuber disease, is smaller than a virus, consists only of free, low molecular weight RNA folded upon itself, and completely lacks the protein capsid that characterises viruses.
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