Ch 1Living World — Class 11 Botany, concept-first.

Earth took shape roughly 4.6 billion years ago and remains, as far as we currently know, the only life-supporting planet - its surface carries landforms such as mountains, plateaus and glaciers, and i…

Every living thing shares a bundle of properties that, together, mark it out from non-living matter - no single property is by itself a perfect test.

A virus is a sub-microscopic, obligate intracellular parasite - meaning it can only multiply inside a living host cell and is completely inert outside one.

The timeline of Virology traces how scientists gradually worked out that something smaller than bacteria, and stranger than ordinary microbes, was behind certain infections.

Viruses are ultramicroscopic - far too small to see with an ordinary light microscope - typically ranging from about 20 to 300 nanometres across (1 nm = 10^-9 m).

Viruses are unusual precisely because they show real, undeniable traits of both the living and the non-living world at once.

Many classification schemes have been proposed for viruses, but the one in general use is David Baltimore's 1971 scheme, which sorts viruses into seven classes purely by molecular criteria: the nature…

Tobacco Mosaic Virus (TMV) was the virus that founded the discipline of virology, being the first agent shown (by Ivanowsky, 1892) to be smaller than a bacterium, and the first virus ever crystallised…

A bacteriophage ('eater of bacteria', from the Greek phagein, to eat) is simply a virus that infects bacteria; phages are abundant wherever bacteria are, including soil, sewage water, fruits, vegetabl…

Phages multiply through one of two very different life cycles. In the lytic (virulent) cycle, the host cell is ultimately destroyed to release new virus particles, through five defined steps: (i) Adso…

Viruses cause disease across the living world - in plants (e.g. tobacco mosaic, cauliflower mosaic, rice tungro disease), in domestic animals (e.g.

Once we accept that Earth carries both living and non-living things side by side, the obvious next question is how to make sense of the sheer variety of living things - millions of species, each with…

Classification exists to solve four practical problems at once: it lets us relate organisms to one another based on the characteristic features they share; it lets us define any given organism in term…

Classification systems have evolved considerably over time as biologists found new criteria to sort organisms by.

R.H. Whittaker, an American taxonomist, proposed the Five Kingdom classification in 1969, sorting all life into Monera, Protista, Fungi, Plantae and Animalia, using a combined set of criteria: cell st…

Bacteria are prokaryotic, unicellular, microscopic organisms found essentially everywhere (ubiquitous); the field that studies them is Bacteriology.

Bacteriology's key milestones run from C.G. Ehrenberg coining the very word 'Bacterium' in 1829, through Christian Gram's differential staining method (1884) and David Bergey's first Manual of bacteri…

Bacteria share a consistent set of general features. They are prokaryotic, so they lack a nuclear membrane and any membrane-bound organelles.

A bacterial cell, from the outside in, reveals three broad layers: (i) the capsule/glycocalyx, (ii) the cell wall, and (iii) the cytoplasm, the last of which houses several distinct internal structure…

Christian Gram, a Danish physician, developed this differential staining procedure in 1884 to sort bacteria into two classes based purely on their cell-wall chemistry.

Bacteria are grouped by how they respire: aerobic bacteria require oxygen as their terminal electron acceptor and cannot grow without it (e.g.

Bacteria reproduce asexually through binary fission, conidia formation and endospore formation, of which binary fission is by far the most common: under favourable conditions the nuclear material divi…

Bacteria have a genuinely two-sided economic impact. On the beneficial side, they underpin soil fertility through ammonification (Bacillus ramosus, Bacillus mycoides converting dead organic matter int…

Archaebacteria are primitive prokaryotes uniquely adapted to survive in extreme environments - hot springs, highly saline water, low pH - and most of them are chemoautotrophic.

Cyanobacteria, popularly called Blue Green Algae or Cyanophyceae, are ancient, photosynthetic, prokaryotic organisms.

Mycoplasma (also called Mollicutes) are very small (0.1-0.5 um), pleomorphic (variable-shaped), Gram-negative micro-organisms, first isolated by Nocard and co-workers in 1898 from the pleural fluid of…

Actinomycetes (Actinobacteria), nicknamed 'Ray fungi' for their fungus-like, mycelial pattern of growth, are in fact Gram-positive bacteria - anaerobic or facultatively anaerobic, and notable for havi…

Fungi (from the Latin fungus, 'mushroom') are ubiquitous, eukaryotic organisms that lack chlorophyll and are therefore always heterotrophic; they exist in both unicellular and multicellular forms, and…

Mycology's key milestones run from P.A. Micheli's pioneering spore-culture experiments (1729, earning him recognition as the founder of Mycology) and Fontana's proof that fungi can cause plant disease…

Most fungi are built from thin, branching, filamentous structures called hyphae, and a mass of interwoven hyphae together forms the mycelium.

Fungi reproduce both asexually and sexually. Asexual methods include: zoospores (flagellate cells produced inside a zoosporangium, e.g. Chytrids); conidia (spores produced on a conidiophore, e.g.

Traditionally, fungi have been split into four classes - Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes - of which Phycomycetes is really an umbrella term covering the Oomycetes, Chytrid…

Formally, Kingdom Myceteae (Fungi) is defined as achlorophyllous, saprophytic or parasitic organisms, unicellular or multicellular (with a mycelium), surrounded by a chitinous cell wall, absorptive in…

Fungi cut both ways economically. Their beneficial roles span several areas. As food, mushrooms such as Lentinus edodes, Agaricus bisporus and Volvariella volvacea are eaten for their high nutritive v…

Class - Zygomycetes; Order - Mucorales; Family - Mucoraceae; Genus - Rhizopus. Rhizopus, popularly called bread mould, is a saprophyte that grows on substrates such as bread, jelly, leather and decayi…

Class - Basidiomycetes; Order - Agaricales; Family - Agaricaceae; Genus - Agaricus. Agaricus is a saprophytic fungus found on wood logs, manure piles, fresh litter and pastures; several species (e.g.

Mycorrhizae is the name for the symbiotic partnership between fungal mycelium and the roots of plants: the fungus draws its own nutrition from the root, while in return its extensive hyphal network im…

A lichen is the symbiotic partnership between an alga and a fungus: the algal partner is called the phycobiont (or photobiont) and the fungal partner the mycobiont.

This end-of-chapter Evaluation checks recall and application across the whole chapter: identifying true statements about virus biology, reading the Gram-staining comparison table correctly, recognisin…

Sample papers and previous-year board questions for this subject.