(a) Define air pollution. Explain the types, sources, consequences and control measures of air pollution. 20 (b) Define…

(a) Air pollution: types, sources, consequences and control

The World Health Organization defines air pollution as the contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere. Physically, air pollutants exist as particulate matter (PM₂.₅, PM₁₀, soot) or as gaseous pollutants (SO₂, NOₓ, CO). By origin, they are classified into primary pollutants, discharged directly into the atmosphere (e.g., SO₂, unburnt hydrocarbons), and secondary pollutants, formed through chemical reactions in the atmosphere (e.g., tropospheric ozone and peroxyacetyl nitrate in photochemical smog).

Sources are twofold. Natural sources comprise volcanic eruptions releasing sulphur compounds, forest fires emitting smoke, and dust storms. Anthropogenic sources include vehicular exhaust, coal-based thermal power stations, metallurgical and chemical industries, domestic solid-fuel use, and biomass burning such as agricultural stubble.

The consequences are systemic. In humans and animals, inhaled particulates and gases impair alveolar gas exchange, leading to chronic obstructive pulmonary disease (COPD), asthma, lung cancer and cardiovascular stress. Environmentally, oxidation of atmospheric SO₂ and NOₓ produces sulphuric and nitric acids that fall as acid rain. Acid deposition lowers the pH of freshwater and soil, leaches cationic nutrients (Ca²⁺, Mg²⁺) and mobilises toxic aluminium ions; atmospheric nitrogen deposition also adds to the eutrophication of water bodies. Greenhouse gases (CO₂, CH₄) enhance radiative forcing, driving global warming and altered precipitation regimes.

Control measures require combined approaches:

• Legislative and policy: the Air (Prevention and Control of Pollution) Act, 1981; Bharat Stage VI emission norms (nationwide from 1 April 2020); the National Clean Air Programme (2019); and the Graded Response Action Plan in the NCR.
• Technological: electrostatic precipitators and fabric filters to arrest fly ash; wet scrubbers and flue-gas desulphurisation to remove SO₂; and three-way catalytic converters in vehicles to oxidise CO and hydrocarbons while reducing NOₓ.
• Biological: green belts around industrial corridors using tolerant species (Ficus religiosa, Azadirachta indica) that act as particulate sinks.

(b) Pheromones and alarm spreading in animals

Karlson and Lüscher (1959) defined pheromones as substances secreted to the outside by an individual and received by a second individual of the same species, in which they release a specific behavioural or developmental response. They differ from interspecific semiochemicals, namely allomones (which benefit the emitter) and kairomones (which benefit the receiver).

Alarm pheromones coordinate anti-predator defence through a causal sequence: a noxious stimulus or tissue injury triggers immediate exocrine secretion; the volatile chemical disperses along a concentration gradient; it binds to chemoreceptors on the antennae or olfactory epithelium of conspecifics; and signal transduction triggers rapid behaviour such as aggression, aggregation or flight.

• Honeybees (Apis mellifera): when a worker stings, the sting apparatus releases isoamyl acetate (Koschevnikov gland), with 2-heptanone from the mandibular glands, recruiting guard bees to attack the intruder.
• Ants (Formica spp.): alarmed workers emit formic acid and undecane from the poison and Dufour's glands, triggering frantic running, jaw-gaping and biting.
• Fishes (superorder Ostariophysi): injury to specialised epidermal club cells releases the alarm substance Schreckstoff; hypoxanthine-3-N-oxide and, more recently, chondroitin sugar fragments have been identified as active components. Nearby shoal members respond by dashing, tighter schooling or freezing near the bottom.
• Aphids: attack by ladybird beetles triggers secretion of (E)-β-farnesene from the cornicles, causing nearby colony members to withdraw their stylets and drop off the host plant.

(c) DNA fingerprinting and forensic applications

Developed by Alec Jeffreys (1984) and pioneered in India by Lalji Singh at CCMB, Hyderabad, DNA fingerprinting (DNA profiling) identifies individuals from polymorphic, non-coding, tandemly repeated DNA sequences that vary greatly between people.

The mechanism follows a definite sequence:

1. Extraction: genomic DNA is isolated from biological evidence (blood, semen, hair roots, buccal swabs).
2. Cleavage or amplification: DNA is digested with restriction endonucleases to release Variable Number of Tandem Repeat (VNTR) fragments, or specific Short Tandem Repeat (STR) loci are amplified by multiplex polymerase chain reaction (PCR).
3. Separation: fragments are separated by size through agarose gel electrophoresis (RFLP-VNTR) or automated capillary electrophoresis (STR).
4. Blotting and hybridisation: in classical RFLP-VNTR analysis, fragments are transferred to a nitrocellulose or nylon membrane by Southern blotting and hybridised with labelled locus-specific probes.
5. Detection: autoradiography or laser-induced fluorescence produces a band or peak pattern (the DNA profile) unique to each individual except monozygotic twins.

In forensic science, the technique gives decisive evidence in several areas:

• Criminal identification: matches biological evidence from crime scenes to suspects; the first conviction using DNA fingerprinting was the Colin Pitchfork case in the UK (1988), and DNA evidence was central in India's Nirbhaya case.
• Paternity and kinship disputes: resolves parentage because each child inherits one STR allele at each locus from each parent.
• Exoneration: secures the release of wrongly convicted persons through retesting of preserved evidence.
• Disaster victim identification: identifies degraded remains after air crashes or mass-casualty events by matching STR profiles with relatives' reference samples.
• Wildlife forensics: used by the Wildlife Institute of India to trace seized tiger skins, ivory and deer meat to species and source populations, curbing illegal trade.