UPSC 2021: Nexus 21—30

Ecology, Biogeochemical Systems & Microscopic Foundations. [Set A]

Question 21

Economic Botany

Which one of the following is used in preparing a natural mosquito repellent?

(a) Congress grass
(b) Elephant grass
(c) Lemongrass
(d) Nut grass

Official Verdict: (c) Lemongrass

The Core Concept: Lemongrass (Cymbopogon) contains potent essential aromatic oils like citronella and citral. These natural terpenes overwhelm and mask the carbon dioxide and lactic acid scents that mosquitoes use to locate human hosts, making it the primary natural active ingredient in non-synthetic bug repellents. Congress grass (Parthenium) is an allergic invasive weed, while Elephant grass and Nut grass possess no notable insect-repellent essential oils.

Tethered to: REALM 226: Useful Plants & Eco Botany

Question 22

Marine Trophic Ecology

Consider the following kinds of organisms:

Copepods
Cyanobacteria
Diatoms
Foraminifera

Which of the above are primary producers in the food chains of oceans?

Official Verdict: (b) 2 and 3

The Core Concept: Primary producers convert sunlight or inorganic chemicals into organic energy (autotrophs). Cyanobacteria (blue-green photosynthetic bacteria) and Diatoms (single-celled algae with silica glass shells) generate over half the oxygen on Earth and form the photosynthetic base of marine food webs. Conversely, Copepods are tiny crustaceans that graze on phytoplankton (primary consumers/zooplankton), while Foraminifera are predominantly heterotrophic amoeboid protists that consume bacteria and diatoms.

Tethered to: REALM 47: Marine Life

Question 23

Evolutionary Adaptations

Consider the following animals:

Hedgehog
Marmot
Pangolin

To reduce the chance of being captured by predators, which of the above organisms rolls up/roll up and protects/protect its/their vulnerable parts?

Official Verdict: (d) 1 and 3

The Core Concept: Hedgehogs flex specialized dorsal muscles to pull their spine-covered skin over their soft bellies, forming an impenetrable spiky sphere. Pangolins tuck their heads under their tails and roll into an armored ball of razor-edged keratin scales. A Marmot is a heavy diurnal rodent (related to squirrels) that does not roll into a defensive ball; it relies on sentinel alarm whistles, sprint speed, and subterranean burrows to evade predators.

Tethered to: REALM 138: Natural Selection & Adaptation

Question 24

Forest Governance

With reference to the 'New York Declaration on Forests', which of the following statements are correct?

It was first endorsed at the United Nations Climate Summit in 2014.
It endorses a global timeline to end the loss of forests.
It is a legally binding international declaration.
It is endorsed by governments, big companies and indigenous communities.
India was one of the signatories at its inception.

Select the correct answer using the code given below.

Official Verdict: (a) 1, 2 and 4

The Core Concept: The NYDF was introduced at the 2014 UN Climate Summit in New York, setting targets to halve natural forest loss by 2020 and eliminate it by 2030 (1 and 2 are true). It is explicitly a non-legally binding political declaration endorsed broadly by state governments, multinationals, and indigenous coalitions (3 is false; 4 is true). India opted out of signing at its inception due to concerns regarding sovereign commitments on agricultural and forest policy (5 is false).

Tethered to: REALM 136: Forest Conservation Strategies

Question 25

Environmental Toxicology

Magnetite particles, suspected to cause neurodegenerative problems, are generated as environmental pollutants from which of the following?

Brakes of motor vehicles
Engines of motor vehicles
Microwave stoves within homes
Power plants
Telephone lines

Select the correct answer using the code given below.

Official Verdict: (b) 1, 2 and 4 only

The Core Concept: Airborne magnetite (iron oxide nanoparticles) can penetrate the blood-brain barrier via the olfactory nerve, triggering Alzheimer's-like neurodegenerative stress. These nanoparticles form through high-temperature frictional abrasion in motor vehicle brake pads (1), fuel combustion in vehicle engines (2), and thermal coal combustion in power generation plants (4). Microwave ovens and copper/fiber telephone lines do not generate airborne airborne iron particulate pollution.

Tethered to: REALM 152: Air Pollution

Question 26

Marine Biology

Which one of the following is a filter feeder?

(a) Catfish
(b) Octopus
(c) Oyster
(d) Pelican

Official Verdict: (c) Oyster

The Core Concept: Filter feeders feed by straining suspended matter, microalgae, and plankton directly from the water column by pumping it across specialized anatomical sieves. Oysters (bivalve mollusks) draw water across their mucosal gills with microscopic cilia, purifying up to 50 gallons of estuary water daily. Catfish are benthic scavengers/predators, Octopuses are active carnivorous hunters, and Pelicans are visual scoop-predators targeting whole fish.

Tethered to: REALM 47: Marine Life

Question 27

Biogeochemical Dynamics

In case of which one of the following biogeochemical cycles, the weathering of rocks is the main source of release of nutrient to enter the cycle?

(a) Carbon cycle
(b) Nitrogen cycle
(c) Phosphorus cycle
(d) Sulphur cycle

Official Verdict: (c) Phosphorus cycle

The Core Concept: Biogeochemical cycles are classified as gaseous (atmospheric reservoir) or sedimentary (lithospheric reservoir). Carbon, Nitrogen, and early Sulfur steps possess major atmospheric gas reservoirs. The Phosphorus cycle has no meaningful atmospheric or gaseous phase under standard conditions. Its reservoir is almost entirely locked in phosphate minerals within sedimentary rocks; natural rain and weathering break these rocks down to release bio-available orthophosphate into soils and waterways.

Tethered to: REALM 32: Phosphorus Cycle

Question 28

Trophic Decomposition

Which of the following are detritivores?

Earthworms
Jellyfish
Millipedes
Seahorses
Woodlice

Select the correct answer using the code given below.

Official Verdict: (c) 1, 3 and 5 only

The Core Concept: Detritivores are heterotrophic organisms that ingest and internally digest decomposing plant and animal detritus and feces. Earthworms ingest soil organic debris, Millipedes consume rotting leaves and wood, and Woodlice shred decaying plant materials. Jellyfish are carnivorous pelagic predators equipped with stinging nematocysts, while Seahorses are carnivorous marine predators feeding on live zooplankton and tiny crustaceans.

Tethered to: REALM 24: Decomposition

Question 29

Built Environment Carbon Accounting

The 'Common Carbon Metric', supported by UNEP, has been developed for

(a) assessing the carbon footprint of building operations around the world
(b) enabling commercial farming entities around the world to enter carbon emission trading
(c) enabling governments to assess the overall carbon footprint caused by their countries
(d) assessing the overall carbon footprint caused by the use of fossil fuels by the world in a unit time

Official Verdict: (a) assessing the carbon footprint of building operations...

The Core Concept: Buildings account for approximately 40% of global energy consumption and a third of worldwide greenhouse gas emissions. The UNEP Sustainable Buildings and Climate Initiative (SBCI) created the Common Carbon Metric (CCM) as a universal, measurable methodology to quantify energy use and carbon emissions per square meter of building floor area ($kgCO_2e/m^2/year$), establishing verified baselines for green building benchmarking.

Tethered to: REALM 183: Circular Economy

Question 30

Symbiotic Phylogenetics

Which of the following have species that can establish symbiotic relationship with other organisms?

Cnidarians
Fungi
Protozoa

Select the correct answer using the code given below.

Official Verdict: (d) 1, 2 and 3

The Core Concept: All three groups are masters of symbiosis. Cnidarians (like reef-building corals and sea anemones) host photosynthetic zooxanthellae or shelter clownfish. Fungi form mycorrhizal partnerships with over 90% of land plant roots and integrate with algae to build lichens. Protozoa live as essential mutualists in the digestive tracts of termites and ruminants (e.g., flagellates that break down raw cellulose).

Tethered to: REALM 48: Coral Reef Ecosystems