Ecology Basics — Set 3

Correct Answer: D. Earthworm

• **Earthworm** = called the 'Friend of the Farmer' because it improves soil aeration, fertility, and structure by tunneling through the ground. • **Castings as natural fertilizer** — earthworm excretions (castings) are rich in nitrogen, phosphorus, and potassium, acting as an excellent natural fertilizer. • 💡 Wrong-option analysis: Ant: aerates soil slightly but not a major soil fertility contributor; Butterfly: a pollinator, not directly related to soil ecology; Honeybee: a key pollinator for crops but does not improve soil quality.

Correct Answer: C. Solar radiation

• **Solar radiation** = the ultimate primary source of energy for nearly all life on Earth, captured by plants through photosynthesis and converted into food. • **Hydrothermal vent exception** — deep-sea hydrothermal vent ecosystems are the rare exception, using chemical energy (chemosynthesis) instead of sunlight. • 💡 Wrong-option analysis: Tidal energy: mechanical energy from tides, not used by life as a biological energy source; Wind: derived from solar energy but not directly usable by ecosystems; Geothermal heat: only used by chemosynthetic deep-sea organisms, not mainstream ecosystems.

Correct Answer: C. Maximum growth rate of a population under ideal conditions

• **Biotic Potential** = the maximum reproductive capacity of an organism under ideal (unlimited resources, no predators, no disease) conditions. • **Environmental Resistance** — in reality, biotic potential is checked by environmental resistance (limited food, predation, disease), preventing runaway population growth. • 💡 Wrong-option analysis: Energy used by a community: this is net community productivity; Total number of species: this is species richness/diversity; Number of deaths: this is mortality rate.

Correct Answer: D. Photosynthesis

• **Photosynthesis** = the process by which green plants remove CO2 from the atmosphere and, using sunlight and water, produce glucose and oxygen. • **Carbon fixation** — photosynthesis is described as 'fixing' atmospheric carbon into organic molecules, playing a key role in regulating Earth's carbon cycle. • 💡 Wrong-option analysis: Decomposition: releases CO2 back to atmosphere, not removes it; Combustion: burning releases stored carbon as CO2, adding to atmosphere; Respiration: releases CO2 as waste, does not remove it.

Correct Answer: C. Commensalism

• **Commensalism** = the shark-remora relationship is a classic (+, 0) interaction: the remora gains transport and protection by attaching to the shark, while the shark is unaffected. • **(+, 0) notation** — commensalism is symbolised as (+, 0): the first organism benefits (+) and the second is neither helped nor harmed (0). • 💡 Wrong-option analysis: Parasitism: (+, -) — remora does not harm the shark; Competition: (-, -) — both would be harmed, but shark is unaffected; Mutualism: (+, +) — requires both to benefit, but shark gains nothing.

Correct Answer: D. Mutualism

• **Mutualism** = a (+, +) interaction where both participating species derive benefits from each other, as in the lichen relationship between fungi and algae. • **Lichen example** — fungi provide structural support and water to algae; algae provide food through photosynthesis — a textbook mutualism. • 💡 Wrong-option analysis: Predation: (+, -) — predator benefits, prey is harmed; Parasitism: (+, -) — parasite benefits, host is harmed; Amensalism: (-, 0) — one is harmed, the other is unaffected.

Correct Answer: C. Population

• **Population** = a group of individuals of the same species inhabiting the same geographic area at the same time, whose size is influenced by birth rate, death rate, and migration. • **Population ecology** — the branch of ecology studying factors affecting population growth, including carrying capacity, biotic potential, and age structure. • 💡 Wrong-option analysis: Biosphere: sum of all ecosystems on Earth; Biome: a large geographical region defined by climate and dominant vegetation; Community: all populations of different species living together in an area.

Correct Answer: C. Phosphorus cycle

• **Phosphorus cycle** = a sedimentary biogeochemical cycle whose primary reservoir is the Earth's crust (rocks), with no significant gaseous phase in the atmosphere. • **Rock weathering** — phosphorus enters the soil through weathering of phosphate-containing rocks, distinguishing it from gaseous cycles like nitrogen or carbon. • 💡 Wrong-option analysis: Oxygen cycle: gaseous cycle with atmospheric reservoir; Carbon cycle: gaseous cycle with atmospheric CO2 as reservoir; Nitrogen cycle: gaseous cycle with atmospheric N2 as primary reservoir.

Correct Answer: C. Eurythermal

• **Eurythermal** = organisms that can survive and function across a broad temperature range, such as most mammals that inhabit diverse climates. • **Stenothermal (opposite)** — stenothermal organisms tolerate only a narrow temperature range; many tropical fish and coral reef organisms are examples. • 💡 Wrong-option analysis: Euryhaline: organisms tolerant of a wide range of salinity, not temperature; Stenohaline: organisms tolerant of only a narrow salinity range; Stenothermal: organisms limited to a very narrow temperature range, opposite of eurythermal.

Correct Answer: B. Biomagnification

• **Biomagnification** = the progressive increase in concentration of toxic, non-biodegradable substances (like DDT or mercury) at each successive trophic level in a food chain. • **Top predators most affected** — substances like DDT accumulate in fatty tissues and cannot be excreted, reaching highest concentrations in apex predators like eagles and humans. • 💡 Wrong-option analysis: Bioremediation: using organisms to clean up pollutants from the environment; Biodiversification: increase in biodiversity, not a toxin-related term; Biofortification: increasing nutritional value of crops, unrelated to toxin accumulation.