Ecology Basics — Set 5

Correct Answer: A. Carbon Cycle

• **Carbon Cycle** = a major gaseous biogeochemical cycle with its primary reservoir in the atmosphere as CO2, driven by photosynthesis and respiration. • **Atmospheric CO2 reservoir** — photosynthesis fixes atmospheric CO2 into organic matter; respiration and decomposition return it to the atmosphere, completing the cycle. • 💡 Wrong-option analysis: Sulphur Cycle: partly sedimentary with rock reservoirs; Calcium Cycle: primarily sedimentary, locked in limestone and chalk; Phosphorus Cycle: strictly sedimentary with no atmospheric gaseous phase.

Correct Answer: D. Carrying Capacity

• **Carrying Capacity** = the maximum population size an environment can sustain indefinitely given available resources, represented by 'K' in population models. • **Symbol 'K'** — carrying capacity (K) is the upper limit of the S-shaped (logistic) population growth curve; beyond K, resources deplete and population declines. • 💡 Wrong-option analysis: Biotic Potential: maximum reproductive capacity under ideal conditions, not the limit set by the environment; Productivity: rate of biomass production; Standing Crop: current biomass at a specific time, not the maximum supportable.

Correct Answer: D. Consumers

• **Consumers** = heterotrophs that cannot produce their own food and must ingest other organisms, classified as primary (herbivores), secondary, and tertiary consumers. • **Heterotrophs** — all animals are consumers because they are heterotrophs unable to synthesise food from inorganic sources; they depend on autotrophs directly or indirectly. • 💡 Wrong-option analysis: Autotrophs: self-feeders that make their own food, opposite of consumers; Saprophytes: decomposers feeding on dead matter, a specialised type of consumer; Producers: autotrophs that produce food, not consumers.

Correct Answer: A. Synecology

• **Synecology** = community ecology studying interactions within and between groups of species and their environment, examining how different populations coexist. • **Synecology vs Autecology** — synecology studies the whole community (many species together); autecology studies a single species in isolation. • 💡 Wrong-option analysis: Autecology: study of a single species and its environment; Genecology: study of genetic variation in relation to environment; Phytogeography: study of geographical distribution of plants.

Correct Answer: D. Tropical Rainforests

• **Tropical Rainforests** = have the highest primary productivity in terrestrial ecosystems due to abundant sunlight, year-round warm temperatures, and high rainfall. • **Highest biodiversity** — this massive energy production supports the highest biodiversity on Earth; coral reefs are comparably productive in aquatic ecosystems. • 💡 Wrong-option analysis: Open Oceans: vast area but low productivity per unit area due to low nutrient content; Tundra: very low productivity due to extreme cold and short growing seasons; Deserts: very low productivity due to water scarcity.

Correct Answer: D. Green plant

• **Green plant (producer)** = always the first link in a grazing food chain, performing photosynthesis to produce organic matter from sunlight, CO2, and water. • **Grazing vs Detritus chain** — in a grazing food chain, energy flows from living producers to consumers; in a detritus food chain, energy flows from dead organic matter to decomposers. • 💡 Wrong-option analysis: Carnivore: third or higher link in a grazing chain; Herbivore: second link (primary consumer), not the first; Decomposer: starts the detritus food chain, not the grazing chain.

Correct Answer: A. Forest (Single tree ecosystem)

• **Forest (Single tree ecosystem)** = the only case where the Pyramid of Numbers is inverted: one large tree (producer) supports many herbivorous insects, and even more parasites. • **Inverted due to parasites** — in a single-tree system, individual numbers increase at each trophic level as one tree hosts hundreds of insects hosting thousands of parasites. • 💡 Wrong-option analysis: Grassland: upright pyramid of numbers with many grass plants; Desert: upright pyramid with sparse but numerous producers; Pond: inverted biomass pyramid, but the number pyramid may be upright.

Correct Answer: A. Biosphere

• **Biosphere** = the worldwide sum of all ecosystems, representing the global zone of life on Earth and integrating all living beings and their relationships. • **Largest ecological unit** — the biosphere is the highest level of ecological organisation, encompassing all life from the deepest ocean trenches to high mountain peaks. • 💡 Wrong-option analysis: Atmosphere: the gaseous envelope around Earth, one component within which life exists; Hydrosphere: all water on Earth, one component of the biosphere; Lithosphere: the solid rock layer of Earth, the physical substrate but not 'all ecosystems'.

Correct Answer: D. (+, +)

• **Mutualism = (+, +)** = both interacting species derive benefits from each other, as in the bee-flower relationship where bees get nectar and flowers get pollinated. • **Symbolic notation** — ecological interactions are expressed as: (+, +) mutualism, (+, -) parasitism/predation, (+, 0) commensalism, (-, -) competition, (-, 0) amensalism. • 💡 Wrong-option analysis: (-, -): competition, where both species are harmed by the interaction; (+, 0): commensalism, one benefits and other is unaffected; (+, -): parasitism or predation, one benefits and the other is harmed.

Correct Answer: C. 2.5%

• **2.5%** = the fraction of Earth's total water that is freshwater; the remaining 97.5% is saline ocean water. • **Glaciers hold most freshwater** — of the 2.5% freshwater, about 68.7% is locked in ice caps and glaciers; only ~0.3% is in accessible surface water like rivers and lakes. • 💡 Wrong-option analysis: 5%: more than double the actual percentage; 10%: four times the actual percentage; 25%: a vastly incorrect figure, implying a quarter of Earth's water is fresh.