Q.(a) Mention the name of man-made cereal. How is it formed ? OR

(a) Triticale is a man-made wheat x rye hybrid with doubled chromosomes; (b) an ecological pyramid's shape varies with the ecosystem and the quantity (numbers/biomass/energy) being plotted at each trophic level.

(a) Man-made cereal -- Triticale

Triticale is the classic example of a man-made (artificial) cereal, created deliberately by plant breeders rather than arising naturally. It is produced by hybridising wheat (Triticum species), which contributes high grain yield and good baking/grain quality, with rye (Secale cereale), which contributes hardiness, disease resistance, and tolerance of poor soil and adverse climatic conditions.

When wheat and rye are crossed, the resulting F1 hybrid is normally sterile, because the chromosome sets contributed by the two different genera are too dissimilar to pair properly during meiosis. To overcome this sterility, the hybrid's chromosome number is doubled by treatment with the chemical colchicine, which inhibits spindle-fibre formation during cell division and so prevents chromosomes from separating, doubling the chromosome number in the affected cells. This produces a fertile amphidiploid (allopolyploid) -- Triticale -- which now carries two complete, pairable chromosome sets, one from wheat and one from rye, restoring normal meiotic pairing and fertility, while combining the high yield of wheat with the hardiness of rye.

(b) Why the shape of the ecological pyramid differs

An ecological pyramid graphically represents the number of organisms, total biomass, or total energy present at each successive trophic level of a food chain, stacked from producers at the base upward through the consumer levels. The shape of this pyramid is not fixed -- it varies both with the type of pyramid being plotted (numbers, biomass, or energy) and with the particular ecosystem being studied, because it directly reflects the actual population size, biomass, or energy content measured at each trophic level in that specific food chain, and these quantities differ from one ecosystem to another.

• A pyramid of energy is always upright in every ecosystem, since energy is progressively lost (mostly as heat via respiration) at each trophic transfer, so the energy available necessarily decreases at each higher level. …