(a) What are the different types and causes of seed dormancy ? Describe various methods used to overcome it. Is it an ecological…

(a) Seed dormancy: types, causes, breaking methods and ecological adaptation Seed dormancy is the failure of a viable seed to germinate under otherwise favourable conditions. Types and causes: exogenous (imposed by structures outside the embryo): physical dormancy from a hard, water-impermeable seed coat (Canna, Lathyrus, legumes); mechanical dormancy from a tough coat or pericarp resisting radicle growth (walnut); chemical dormancy from inhibitors such as ABA, phenolics, coumarin in fruit pulp or coat (tomato, Xanthium). Endogenous: morphological dormancy (underdeveloped embryo, e.g., Ginkgo, orchids) and physiological dormancy (high ABA to GA ratio, needing after-ripening or chilling). Combinational types occur too. Breaking methods: mechanical or acid scarification (conc. H2SO4 for legumes), hot-water treatment, stratification at 0–5 °C (apple, peach), leaching with water, GA3 or cytokinin and KNO3 soaking, light exposure (lettuce, phytochrome), alternating temperatures and after-ripening storage. Ecological adaptation: it prevents germination in the unfavourable season, spreads germination in time (hedging risk), builds a persistent soil seed bank, and times seedling emergence with rain or spring; it also aids dispersal in time and recovery after fire or disturbance.

(b) Sustainable development Sustainable development, defined by the Brundtland Commission (1987), is “development that meets the needs of the present without compromising the ability of future generations to meet their own needs.” Objectives: maintain ecological integrity and biodiversity; use renewable resources within regeneration limits; ensure economic growth with equity and poverty removal; reduce pollution and waste; protect the carrying capacity of ecosystems; and give people participation in decisions. Its three pillars are economic, social and environmental, with environmental limits as the base. Importance: it protects the resource base for future generations, balances development with conservation, curbs climate change, and gives a policy framework through Agenda 21 (1992), the Sustainable Development Goals (2030 Agenda, 17 goals) and the Paris Agreement. In India it is reflected in renewable-energy targets, forest-cover policies, and watershed and organic farming programmes.

(c) Endemism Endemism is the restriction of a species or taxon to a particular geographic area and found nowhere else. Categories: by area (local, regional, national, continental); by origin: palaeo-endemics (relict old taxa such as Cycas beddomei, restricted by extinction elsewhere) and neo-endemics (recently evolved, e.g., many Western Ghats herbs); and by ecology, such as habitat endemics on islands or mountains. Causes: geographic isolation (islands, mountain tops), speciation, narrow ecological tolerance and past climate refugia. Examples: Nepenthes khasiana (Meghalaya), Pinanga dicksonii (Western Ghats), many orchids of the Eastern Himalaya, Andaman and Nicobar species. Endemism differs from rarity, since an endemic can be locally abundant. Because small ranges raise extinction risk, endemics need priority: protection in biodiversity hotspots, IUCN Red List assessment, in-situ protected areas and ex-situ gene banks, habitat restoration and control of invasive species.