Ecology Basics — Set 2

Correct Answer: B. Saprophytes

• **Saprophytes** = organisms such as many fungi and bacteria that obtain nutrients from dead organic material by secreting enzymes that break down complex molecules. • **Nutrient cycling** — saprophytes (decomposers) play a vital role by releasing essential nutrients back into the soil and atmosphere for producers to reuse. • 💡 Wrong-option analysis: Symbionts: organisms living in symbiosis, not specifically dead-matter feeders; Parasites: feed on living hosts, not dead matter; Predators: actively hunt and kill living prey.

Correct Answer: D. Niche

• **Niche** = the functional role and position of a species in its ecosystem, encompassing what it eats, where it lives, and how it interacts with other species. • **'Profession' vs 'Address'** — the niche is a species' ecological 'profession', while habitat is its 'address'; no two species can occupy the exact same niche indefinitely (Competitive Exclusion Principle). • 💡 Wrong-option analysis: Range: the geographic area a species is found in; Biome: a large-scale climate-defined region; Habitat: the physical 'address' or location where an organism lives, not its functional role.

Correct Answer: B. Biogeochemical Cycle

• **Biogeochemical Cycle** = the movement of nutrients like carbon, nitrogen, and phosphorus between the living (biotic) and non-living (abiotic) parts of an ecosystem. • **Gaseous vs Sedimentary** — biogeochemical cycles are broadly classified into gaseous cycles (C, N, O with atmospheric reservoir) and sedimentary cycles (P, S with crustal reservoir). • 💡 Wrong-option analysis: Sedimentation: deposition of sediment, not nutrient cycling; Energy Flow: unidirectional movement of energy, not cyclic; Ecological Pyramid: visual representation of trophic levels, not nutrient movement.

Correct Answer: C. Grasshopper

• **Grasshopper** = a primary consumer in the grassland ecosystem, feeding directly on grass (the producer) and occupying the second trophic level. • **Second trophic level** — primary consumers (herbivores) are the first animals in a food chain; organisms eating them are secondary consumers. • 💡 Wrong-option analysis: Grass: the producer at the first trophic level, not a consumer; Lion: a tertiary/apex consumer at the top; Snake: a secondary consumer feeding on grasshoppers and frogs.

Correct Answer: A. Standing Crop

• **Standing Crop** = the total biomass of living organisms in a given area at a specific point in time, expressed as mass or number per unit area. • **Standing Crop vs Standing State** — 'Standing Crop' refers to living biomass, while 'Standing State' refers to the amount of inorganic nutrients present in an ecosystem. • 💡 Wrong-option analysis: Standing State: refers to inorganic nutrient quantities, not living biomass; Gross Production: total photosynthesis rate before respiration losses; Net Production: gross production minus respiration, the biomass available to consumers.

Correct Answer: D. Commensalism

• **Commensalism** = a (+, 0) interaction where one species gains benefit while the other is completely unaffected, neither helped nor harmed. • **Orchid on a mango tree** — a classic commensalism example: the orchid gets support and sunlight while the tree is unaffected. • 💡 Wrong-option analysis: Amensalism: (-, 0) — one is harmed while the other is unaffected; Parasitism: (+, -) — one benefits while the other is harmed; Mutualism: (+, +) — both species benefit from the interaction.

Correct Answer: C. Ecotone

• **Ecotone** = the ecological area where the 'Edge Effect' is primarily observed, with higher species density and diversity than in either flanking community. • **Forest-grassland edge** — the Edge Effect is especially noticeable in bird populations at forest-grassland boundaries, where species from both habitats overlap. • 💡 Wrong-option analysis: Core of a forest: low diversity ecotone area, not an edge; Desert center: monotonous habitat with low species diversity; Open ocean: pelagic zone, no habitat boundary effects.

Correct Answer: C. Nitrogen Fixation

• **Nitrogen Fixation** = the process converting atmospheric N2 into ammonia or nitrates, carried out by bacteria like Rhizobium in legume root nodules or by lightning. • **Rhizobium** — the key nitrogen-fixing bacterium living in root nodules of leguminous plants, supplying biologically fixed nitrogen directly to the host plant. • 💡 Wrong-option analysis: Ammonification: decomposition of organic nitrogen to ammonia; Nitrification: conversion of ammonia to nitrites and then nitrates by bacteria; Denitrification: conversion of nitrates back to atmospheric N2, opposite of fixation.

Correct Answer: A. Pond

• **Pond (aquatic ecosystem)** = has an inverted biomass pyramid because fish biomass far exceeds phytoplankton biomass at any given time. • **High phytoplankton turnover** — phytoplankton have a very high reproduction rate (turnover), so despite small standing crop at any moment, they support much larger fish populations. • 💡 Wrong-option analysis: Desert: upright biomass pyramid with sparse but stable vegetation; Forest: strongly upright biomass pyramid with massive tree biomass at producer level; Grassland: typically upright biomass pyramid.

Correct Answer: A. Resilience

• **Resilience** = the ecological capacity of an ecosystem to absorb disturbances and return to its original stable state after being displaced. • **Biodiversity increases resilience** — ecosystems with higher biodiversity can recover faster from disturbances, making resilience a key reason to conserve species richness. • 💡 Wrong-option analysis: Resistance: the ability to withstand disturbance without changing (different from bouncing back); Adaptation: a genetic/behavioural change in organisms over generations, not an ecosystem property; Succession: the process of ecosystem change over time, not a stability capacity.