Q.Define species diversity, and state one way in which it can be measured for a given region.

Biodiversity is assessed at three nested levels: genetic, species, and ecosystem diversity.

Genetic diversity refers to the variety of genes and alleles present within a single species, which allows different populations/individuals of that species to differ in traits (e.g., the many rice or mango varieties cultivated in India). Species diversity refers to the variety and abundance of different species present in a given region or ecosystem (measured, e.g., by species richness and species evenness) -- India, with about 8% of the world's recorded species despite covering only about 2.4% of the world's land area, is considered a mega-diverse country. Ecosystem diversity refers to the variety of habitats, ecological niches and ecological processes (such as nutrient cycling, energy flow) found within a geographic area -- for example, the diversity of ecosystems within India ranging from deserts to rainforests to coral reefs. All three levels are interlinked and together constitute the full concept of biodiversity.

Air pollutant particulates are classed by size into fine particles (<2.5 µm, PM2.5) and coarse particles (>2.5 µm, up to PM10).

Airborne particulate matter is broadly divided by particle diameter. Fine particles are less than about 2.5 micrometres (µm) in diameter (the 'PM2.5' fraction); they stay suspended in air longer, penetrate deep into the lungs, and include examples like aerosols (fine liquid/solid droplets suspended in gas) and smoke or fumes from combustion. Coarse particles are larger, generally over 2.5 µm in diameter (up to about 10 µm, the 'PM10' fraction); they settle out of the air more quickly and include examples such as carbon particles (soot from incomplete combustion) and windblown dust, grit or pollen grains.