(a) Vermiculture (10 marks) (b) FISH (10 marks) (c) Biological clock (10 marks) (d) Ecological succession (10 marks) (e)…

(a) Vermiculture

Vermiculture is the scientific breeding and rearing of earthworms, and vermicomposting uses them to convert organic waste into vermicompost. Surface-dwelling (epigeic) species are used, mainly Eisenia fetida (red wiggler) and Eudrilus eugeniae, since they feed voraciously on decaying matter, breed fast and tolerate wide changes in conditions.

Method: beds or pits are filled with partly decomposed farm and kitchen waste and cattle dung, kept moist and shaded at about 25–30 °C with neutral pH, and the worms are added. They ingest the waste, which is ground in the gizzard and acted on by gut microflora, and pass out castings. In 40–60 days the castings are harvested, and the worms are used to start new beds.

Vermicompost is porous, holds water well, and is rich in available nitrogen, phosphorus and potassium and in plant growth-promoting substances. It improves soil structure and fertility, and cuts the use of chemical fertilisers. The worms are also used as protein feed for fish and poultry. Vermicomposting is a low-cost way of managing organic waste.

(b) FISH

Fluorescence in situ hybridisation (FISH) is a cytogenetic technique to detect and locate specific DNA or RNA sequences directly on chromosomes or in nuclei. The target DNA on a slide of metaphase chromosomes or interphase nuclei is denatured, and a single-stranded probe labelled with a fluorescent dye, complementary to the sequence of interest, is added to hybridise with it. Unbound probe is washed off and the signals are seen under a fluorescence microscope, where the position and number of the signals are read, often with different colours for several probes.

FISH gives a resolution between that of the karyotype and DNA sequencing. Applications: detecting aneuploidy (such as trisomy 21), microdeletions and translocations in prenatal and clinical diagnosis; cancer cytogenetics, for example BCR-ABL1 in chronic myeloid leukaemia and HER2 amplification in breast cancer; gene mapping; and comparing chromosomes between species.

(c) Biological clock

A biological clock is an internal timing mechanism that makes organisms show rhythms of physiology and behaviour. Rhythms of about 24 hours that persist in constant conditions (free-running) are circadian rhythms; others are tidal, lunar or annual. External cues such as light, called zeitgebers, entrain the clock to the actual day. Examples are the sleep–wake cycle, body temperature, hormone secretion, leaf movement and the emergence of Drosophila.

In mammals the master clock is the suprachiasmatic nucleus (SCN) of the hypothalamus, which receives light information from the retina through the retinohypothalamic tract and controls the pineal secretion of melatonin. At the molecular level a transcription–translation feedback loop operates: CLOCK and BMAL1 proteins activate the genes Period (per) and Cryptochrome (cry); the PER and CRY proteins build up, enter the nucleus and inhibit CLOCK–BMAL1, and then decay, so the cycle restarts in about 24 hours. Disturbed clocks cause jet lag and shift-work disorders.

(d) Ecological succession

Ecological succession is the orderly, directional replacement of one community by another in an area over time until a stable climax community, in balance with the climate, is reached. It starts with pioneer species, passes through intermediate (seral) stages that change the soil and microclimate, and ends in the climax.

• Primary succession begins on a bare area with no soil or life, such as a new rock surface, sand dune, lava flow or a new pond. On a rock (lithosere) lichens come first, then mosses, herbs, shrubs and trees; in a pond (hydrosere) it runs from phytoplankton through submerged and floating plants to reed swamp and meadow.
• Secondary succession begins where an existing community has been removed but soil and seeds remain, for example an abandoned farm field or a burnt or felled forest. It is faster than primary succession.

Succession is driven by modification of the environment by the organisms themselves, so the earlier community prepares the way for the next.

(e) Biodiversity hotspots

A biodiversity hotspot is a region with exceptional endemism that is also highly threatened. Norman Myers' criteria are that it holds at least 1,500 species of endemic vascular plants (over 0.5% of the world's total) and has lost at least 70% of its original natural vegetation. Conservation International recognises 36 hotspots in the world.

Four fall in India: the Himalaya, the Western Ghats and Sri Lanka, Indo-Burma (north-east India) and Sundaland (the Nicobar Islands). The Western Ghats, for example, hold over 3,000 endemic flowering plants and many endemic amphibians and reptiles. The hotspot idea helps to set priorities for conservation funds, protected areas and species recovery.