Tuesday, December 1, 2020

Biological Classification | Plus 1 Botany | Exam Capsule Notes

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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