Write short notes on the following in about 150 words each: 10×5=50 (a) Biodiversity hot spots (b) Navigation in birds (c)…

(a) Biodiversity hot spots

Biodiversity hot spots are regions of exceptional endemic richness under severe threat, a concept formalised by Norman Myers in 1988 to prioritise conservation. A region qualifies if it contains at least 1,500 endemic vascular plant species, representing 0.5% of the world’s vascular flora, and has lost at least 70% of its original habitat. India’s Western Ghats and Himalaya are recognised hot spots. The Western Ghats contain endemic amphibians, reptiles, and birds in sholas, grasslands, and evergreen forests; the Himalaya includes alpine meadows, temperate forests, and high-altitude endemics. Their conservation significance is strategic: protecting these small, species-dense areas can avert mass extinction, preserve ecosystem services and resilience, and guide conservation planning under the Biodiversity Act and national park frameworks. They cover a small fraction of land but hold disproportionate plant and vertebrate endemism. This makes them priority targets for in-situ protected-area expansion, ex-situ conservation, community-based management, and ecological restoration in India.

(b) Navigation in birds

Avian navigation is the capacity of birds to orient and travel over long distances using integrated sensory cues. The sun compass uses the position of the sun corrected by an internal clock; the star compass relies on polarised star patterns around the celestial pole. A magnetic compass, mediated by magnetite in the beak and cryptochrome-based radical-pair mechanisms in the retina, provides directional bearing and inclination. Olfactory maps contribute to route finding, especially in homing and foraging contexts. These cues are not used in isolation; birds integrate them, with priority shifting when one cue is manipulated. The Arctic tern exemplifies long-distance migratory navigation, travelling between polar breeding and wintering grounds. In India, controlled experiments with homing pigeons (Columba livia) show that they can return to lofts after displacement using magnetic, visual, and olfactory information, though they are domesticated rock doves rather than long-distance migrants. These studies clarify cue integration in birds.

(c) Sickle cell anaemia

Sickle cell anaemia is an autosomal recessive haemoglobinopathy caused by a single-base substitution in the β-globin gene, replacing glutamic acid by valine at the sixth position of the β-chain. The resulting HbS has a hydrophobic patch that, under low oxygen tension, polymerises into rigid fibres, distorting erythrocytes into sickle shapes. These cells become sticky, obstruct microvasculature, and lyse, producing chronic haemolytic anaemia, vaso-occlusive crises, splenic infarction, and organ damage. The condition illustrates balancing selection. Heterozygotes carrying one HbS allele (HbAS) have reduced susceptibility to severe Plasmodium falciparum malaria because the parasite’s growth and red-cell survival are impaired, giving a fitness advantage in malarious regions. In India, HbS is uncommon but documented in tribal and isolated populations, notably in Saurashtra and the Nilgiris, where historical malaria pressure may have maintained the allele. Diagnosis uses haemoglobin electrophoresis, HPLC, or DNA testing, and management includes hydration, transfusion, hydroxyurea, and supportive care in India.

(d) Circadian rhythms

Circadian rhythms are endogenous, approximately 24-hour oscillations in physiology, behaviour, and gene expression that persist in constant conditions. In mammals, the master oscillator is the suprachiasmatic nucleus (SCN) of the hypothalamus, which receives retinal input via the retinohypothalamic tract and synchronises peripheral clocks in the liver, skin, and immune cells. Environmental zeitgebers, especially light, temperature, and feeding time, entrain the clock to the local day. Molecularly, the core clock involves positive elements CLOCK and BMAL1, which activate Period (Per) and Cryptochrome (Cry) genes; PER/CRY proteins accumulate, inhibit CLOCK/BMAL1, and create a transcriptional feedback loop. In birds and other animals, similar loops regulate melatonin secretion, body temperature, locomotor activity, and hormone release. Chronobiology applies this knowledge to shift-work health in humans, drug timing (chronopharmacology), treatment of jet lag, and management of sleep disorders. In India, agricultural and veterinary practices also benefit from understanding daily activity patterns in livestock and crop pollinators.

(e) Biome

A biome is a major ecological unit defined by its dominant vegetation, climate, and characteristic biota over a broad geographical area. Unlike an ecosystem, which is a local functional unit of interacting organisms and abiotic factors, a biome is a higher-level pattern that groups similar ecosystems across continents. Whittaker’s classification uses mean annual temperature and precipitation to delineate biomes, producing a matrix in which tropical rain forest, savanna, desert, temperate forest, grassland, tundra, and boreal forest occupy distinct climatic zones. Climate-vegetation coupling is central: rainfall and temperature determine plant form, leaf size, phenology, and productivity, which in turn structure animal communities. In India, tropical thorn forests occur in low-rainfall regions such as parts of Rajasthan and Gujarat, while montane forests show altitudinal zonation from subtropical to temperate and alpine belts in the Himalaya and Western Ghats. Biomes are useful for macroecology, conservation planning, and predicting species distributions under climate change.