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

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:

• Prokaryotes & eukaryotes under Plants.
• Unicellular and multicellular organisms in same group.
• 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).

  

I. Archaebacteria:

• Halophiles: Live in salty areas.
• Thermoacidophiles: In hot springs.
• 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):

• Have chlorophyll a.
• Cyanobacteria (blue-green algae) colonies have gelatinous sheath. Some fix nitrogen in heterocysts. E.g. Nostoc & Anabaena. 

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

c. Heterotrophic bacteria: Most abundant. Decomposers.

Reproduction in Bacteria:

• Mainly by fission.
• Spore formation: Under unfavourable conditions.

Mycoplasmas are the smallest living cells and no cell wall. 

2. KINGDOM PROTISTA 

Single-celled eukaryotes.

Some have flagella or cilia.

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

I. Chrysophytes:

• Diatoms & golden algae (desmids).
• Diatoms have siliceous cell walls. Their cell wall deposit is called diatomaceous earth.

II. Dinoflagellates:

• Mostly marine and photosynthetic.
• Cell wall: stiff cellulose plates. 
• Most have 2 flagella.
• Red dinoflagellates (E.g. Gonyaulax)- sea appears red (red tides).

III. Euglenoids:

• Have a protein rich layer (pellicle) & 2 flagella.
• Photosynthetic in sunlight. Heterotrophs in darkness.
• E.g. Euglena.

IV. Slime Moulds:

• Saprophytic protists.
• Suitable condition → form an aggregation (plasmodium).
• Unfavourable conditions → plasmodium differentiates → fruiting bodies bearing spores.

V. Protozoans:

    They are heterotrophs (predators or parasites).

• Amoeboid protozoans: Move & capture prey by pseudopodia (false feet). E.g. Amoeba, Entamoeba (parasite).
• Flagellated protozoans: Have flagella. Parasites cause diseases like sleeping sickness. E.g. Trypanosoma.
• Ciliated protozoans: Move by cilia. E.g. Paramoecium.
• 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:

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

Reproduction:

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

Sexual cycle has 3 steps:

1. Plasmogamy: Fusion of protoplasm between two motile or non-motile gametes.
2. Karyogamy: Fusion of two nuclei.
3. 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) 

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

II. Ascomycetes (sac-fungi) 

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

III. Basidiomycetes 

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

IV. Deuteromycetes (Imperfect fungi) 

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

VIRUSES, VIROIDS, PRIONS & LICHENS 

Viruses: 

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

Viroid: 

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

Prions: 

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

Lichens: 

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

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