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Biological Classification | Plus 1 Botany | Exam Capsule Notes (Web and PDF)

Biological Classification - Revision Notes
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BIOLOGICAL CLASSIFICATION:
Chapter at a glance

Aristotle’s classification: Plants to trees, shrubs & herbs. Animals to those with red blood & without red blood.

Linnaeus: 2-Kingdom classification (Plantae & Animalia).

Drawbacks:

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Prokaryotes & eukaryotes under Plants.
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Unicellular and multicellular organisms in same group.
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No differentiation between fungi and plants.

R.H. Whittaker: Five-Kingdom Classification.

Characteristics of the five kingdoms
Characters Monera Protista Fungi Plantae Animalia
Cell type Prokaryotic Eukaryotic Eukaryotic Eukaryotic Eukaryotic
Cell wall Polysaccharide + amino acid Present in some Chitin & polysaccharide Cellulose Absent
Nuclear membrane Absent Present Present Present Present
Body organisation Cellular Cellular Multicellular, loose tissue Tissue/ organ Tissue/organ/ organ system
Mode of nutrition Autotrophic, heterotrophic Autotrophic, heterotrophic Heterotrophic Autotrophic Heterotrophic
1. KINGDOM MONERA (BACTERIA)

Most abundant microorganisms.

4 types: Coccus (Spherical), Bacillus (Rod-shaped), Vibrium (Comma-shaped) & Spirillum (Spiral).

Microscopic View of Bacteria Shapes (Coccus, Bacillus, Vibrio, Spirillum)
I. Archaebacteria:
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Halophiles: Live in salty areas.
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Thermoacidophiles: In hot springs.
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Methanogens: In marshy areas and guts of ruminant animals. Produce methane (biogas).
II. Eubacteria (‘true bacteria’):

Rigid cell wall and a flagellum.

a. Photosynthetic autotrophs (E.g. Cyanobacteria):

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Have chlorophyll a.
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Cyanobacteria (blue-green algae) colonies have gelatinous sheath. Some fix nitrogen in heterocysts. E.g. Nostoc & Anabaena.
Filamentous Blue-Green Algae Nostoc Structure Diagram

b. Chemosynthetic autotrophs: Oxidize inorganic substances and release energy.

c. Heterotrophic bacteria: Most abundant. Decomposers.

Reproduction in Bacteria:

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Mainly by fission.
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Spore formation: Under unfavourable conditions.
A Dividing Bacterium Fission Diagram

Mycoplasmas are the smallest living cells and have no cell wall.

2. KINGDOM PROTISTA

Single-celled eukaryotes. Some have flagella or cilia.

Reproduction: Asexual & sexual (cell fusion → zygote).

I. Chrysophytes:
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Diatoms & golden algae (desmids).
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Diatoms have siliceous cell walls. Their cell wall deposit is called diatomaceous earth.
II. Dinoflagellates:
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Mostly marine and photosynthetic.
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Cell wall: stiff cellulose plates. Most have 2 flagella.
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Red dinoflagellates (E.g. Gonyaulax)- sea appears red (red tides).
III. Euglenoids:
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Have a protein rich layer (pellicle) & 2 flagella.
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Photosynthetic in sunlight. Heterotrophs in darkness.
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E.g. Euglena.
IV. Slime Moulds:
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Saprophytic protists.
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Suitable condition → form an aggregation (plasmodium).
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Unfavourable conditions → plasmodium differentiates → fruiting bodies bearing spores.
V. Protozoans:

They are heterotrophs (predators or parasites).

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Amoeboid protozoans: Move & capture prey by pseudopodia (false feet). E.g. Amoeba, Entamoeba (parasite).
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Flagellated protozoans: Have flagella. Parasites cause diseases like sleeping sickness. E.g. Trypanosoma.
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Ciliated protozoans: Move by cilia. E.g. Paramoecium.
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Sporozoans: Have infectious spore-like stage. E.g. Plasmodium (malarial parasite).
3. KINGDOM FUNGI

Except yeasts, fungi are filamentous. Saprophytes. Some are parasites.

Cell wall is made of chitin & polysaccharides.

Hyphae: Thread-like structures of the body.

Mycelium: Network of hyphae.

Hyphae are 2 types:

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Coenocytic hyphae: Continuous tubes with multinucleated cytoplasm.
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Septate hyphae: Have septae or cross walls.

Reproduction:

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Vegetative propagation: Fragmentation, fission & budding.
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Asexual: Spores (conidia, sporangiospores & zoospores).
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Sexual: By oospores, ascospores & basidiospores. They are produced in fruiting bodies.

Sexual cycle has 3 steps:

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Plasmogamy: Fusion of protoplasm between two motile or non-motile gametes.
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Karyogamy: Fusion of two nuclei.
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Meiosis in zygote to give haploid spores.

In sexual reproduction, 2 haploid hyphae fuse. In some fungi, 2 haploid cells fuse → diploid cells (2n).

In ascomycetes & basidiomycetes, a dikaryotic stage or dikaryophase (2 nuclei) occurs. Such condition is called a dikaryon. Later, parental nuclei fuse → diploid.

I. Phycomycetes (Lower Fungi)

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Occur in aquatic habitats and on decaying wood or as obligate parasites on plants.
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Mycelium is aseptate and coenocytic.
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Asexual reproduction: By motile zoospores or by non-motile aplanospores.
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Sexual reproduction: 2 gametes fuse → Zygospores. Gametes are isogamous or anisogamous or oogamous.
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E.g. Mucor, Rhizopus (bread mould) and Albugo (parasitic fungi on mustard).

II. Ascomycetes (sac-fungi)

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Unicellular (e.g. yeast, Saccharomyces) or multicellular (e.g. Penicillium- source of antibiotics).
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Mycelium is branched and septate.
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Asexual reproduction: By conidia produced on conidiophores.
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Sexual reproduction: By ascospores produced in sac like asci. The asci form fruiting bodies (ascocarps).
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E.g. Aspergillus, Claviceps & Neurospora (used in biochemical & genetic work).
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Morels & truffles are edible.

III. Basidiomycetes

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Includes mushrooms, bracket fungi or puffballs.
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The mycelium is branched and septate.
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Vegetative reproduction by fragmentation is common.
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Plasmogamy by fusion of 2 vegetative or somatic cells → dikaryotic structure → basidium → Karyogamy & meiosis → 4 basidiospores.
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Basidia are arranged in fruiting bodies (basidiocarps).
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E.g. Agaricus (mushroom), Ustilago (smut) and Puccinia (rust fungus).

IV. Deuteromycetes (Imperfect fungi)

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Only their asexual or vegetative phases are known.
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They reproduce only by asexual spores (conidia).
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The mycelium is septate and branched.
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Some are saprophytes or parasites. Majority is decomposers.
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E.g. Alternaria, Colletotrichum and Trichoderma.
VIRUSES, VIROIDS, PRIONS & LICHENS

Viruses:

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Non-cellular obligate parasites. So not included in five-kingdom classification.
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Ivanowsky discovered virus. Louis Pasteur gave the name virus.
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Beijerinek demonstrated that the extract (Contagium vivum fluidum) of infected tobacco cause infection in healthy plants.
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W.M. Stanley showed that viruses could be crystallized.
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A virus is a nucleoprotein, i.e. it has a protein coat (capsid) & genetic material (RNA or DNA).
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Generally, plant viruses have single stranded RNA. Animal viruses have either single or double stranded RNA or double stranded DNA.
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Bacteriophages usually have double stranded DNA.
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The capsid is made of small subunits (capsomeres).
Tobacco Mosaic Virus (TMV) and Bacteriophage Structural Diagram

Viroid:

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An infectious agent with small RNA and no protein coat. Discovered by T.O. Diener.
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It causes potato spindle tuber disease.

Prions:

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Abnormally folded protein.
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Cause bovine spongiform encephalopathy (BSE) or mad cow disease in cattle and Cr-Jacob disease (CJD) in humans.

Lichens:

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Symbiotic association between algae & fungi.
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Algal component: Phycobiont (autotrophic). Fungal component: Mycobiont (heterotrophic).
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Lichens are pollution indicators.
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