Biological classification

 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. 

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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.

Scientist names

 

Organic chemistry

 NAMED REACTION 👻👻👻

Disorders

 Disorders (Human physiology)

BREATHING AND EXCHANGE OF GASES

 BREATHING AND EXCHANGE OF GASES

DIGESTION AND ABSORPTION

 DIGESTION AND ABSORPTION 👻