✅ Answer: A) Ernst Haeckel (1866)The term “Ecology” was coined by German biologist Ernst Haeckel in 1866. It comes from Greek “oikos” (house/habitat) + “logos” (study). Ecology is the study of interactions between organisms and their environment. A.G. Tansley coined the term “Ecosystem” in 1935. Lindeman proposed the 10% law of energy transfer in 1942.

✅ Answer: B) 100 kcalAccording to Lindeman’s 10% law (1942), only 10% of energy is transferred from one trophic level to the next. Producers (T1) = 10,000 kcal → Primary consumers (T2) = 1,000 kcal → Secondary consumers (T3) = 100 kcal → Tertiary consumers (T4) = 10 kcal. This is why food chains rarely exceed 4-5 trophic levels — too little energy remains at higher levels.

✅ Answer: C) Pyramid of EnergyThe Pyramid of Energy is always upright and can never be inverted because energy always decreases as it moves up the food chain (due to the 10% law). Pyramid of Numbers can be inverted (e.g., one tree supporting many insects). Pyramid of Biomass can be inverted in aquatic ecosystems (phytoplankton biomass < zooplankton biomass at any given time, though phytoplankton reproduce faster).

✅ Answer: A) RhizobiumRhizobium is a nitrogen-fixing bacterium that lives in symbiosis with legume plants (peas, beans, groundnut, soybean) in root nodules. It converts atmospheric N₂ into ammonia (NH₃) which plants can use. Free-living nitrogen fixers: Azotobacter (aerobic), Clostridium (anaerobic), Cyanobacteria (blue-green algae). Nitrosomonas converts ammonia to nitrites (nitrification). Pseudomonas converts nitrates to N₂ (denitrification).

✅ Answer: B) A.G. Tansley (1935)The term “Ecosystem” was coined by British ecologist A.G. Tansley in 1935. An ecosystem is a functional unit of ecology comprising biotic (living) and abiotic (non-living) components interacting with each other. E.P. Odum is called the “Father of Modern Ecology” for his comprehensive study of ecosystems. Ernst Haeckel coined “Ecology” (1866). Lindeman proposed the 10% law (1942).

✅ Answer: D) Both A and CBoth options A and C are examples of grazing food chains (starting from living plants/producers). Option A: Terrestrial grazing food chain. Option C: Aquatic grazing food chain. Option B is a detritus food chain (starting from dead organic matter). In a grazing food chain, energy flows from living producers to herbivores to carnivores. Detritus food chains start with dead organic matter and are important in forest ecosystems.

✅ Answer: A) GPP − RespirationNet Primary Productivity (NPP) = Gross Primary Productivity (GPP) − Respiration. GPP is the total rate of photosynthesis. NPP is the energy available for consumers (herbivores). Tropical rainforests have the highest NPP (~2,000 g/m²/year). Deserts and tundra have the lowest NPP. Oceans have low NPP per unit area but contribute significantly due to their vast size.

✅ Answer: A) Bare rock or sand with no soilPrimary succession begins on bare rock, sand, or lava flows where no soil exists. Pioneer species (lichens on rock, mosses) colonise first, break down rock, and create soil. This is a very slow process (hundreds to thousands of years). Secondary succession begins where an ecosystem was disturbed but soil remains (abandoned farmland, burned forest). Secondary succession is much faster than primary succession.

✅ Answer: D) Phosphorus cycleThe Phosphorus cycle has no atmospheric phase — phosphorus does not exist as a gas. It cycles through rocks (weathering) → soil → plants → animals → decomposition → back to soil. This makes it the slowest biogeochemical cycle. Phosphorus is a limiting nutrient in aquatic ecosystems. Carbon, nitrogen, and water cycles all have atmospheric phases. Phosphorus is essential for DNA, RNA, ATP, and cell membranes.

✅ Answer: A) Tropical RainforestTropical rainforests have the highest Net Primary Productivity (~2,000 g/m²/year) due to high sunlight, temperature, and rainfall throughout the year. Ranking by NPP: Tropical rainforest > Estuary > Coral reef > Temperate forest > Grassland > Open ocean > Desert/Tundra. Deserts and tundra have the lowest NPP. Estuaries and coral reefs are highly productive aquatic ecosystems.