"Ecology and Environment" — Practice

Question 1

Bears entering a state of reduced metabolic activity during winter is an example of:
(a) hibernation (b) aestivation (c) diapause (d) regulation

Accepted Answer

(a) hibernation.

Hibernation is winter dormancy (reduced metabolism) to survive cold conditions; aestivation is summer dormancy (e.g., snails, some fish) to survive heat/desiccation, and diapause is a resistant inactive stage seen in insects.

Question 2

The logistic population growth model differs from the exponential model in that it incorporates:
(a) a carrying capacity K that limits growth (b) unlimited resource availability (c) a constant growth rate regardless of population size (d) no dependence on population size

Accepted Answer

(a) a carrying capacity K that limits growth.

Logistic growth: dN/dt = rN(K−N)/K — as N approaches the carrying capacity K, growth rate slows toward zero, unlike exponential growth which assumes unlimited resources.

Question 3

A population of 500 bacteria grows exponentially with r = 0.02 per hour. Using Nt = N0(1 + rt) as an approximation for small rt, estimate the population after 10 hours.

Accepted Answer

Nt ≈ N0(1 + rt) = 500 × (1 + 0.02×10) = 500 × 1.2 = 600 bacteria (approximately).

(Note: the exact exponential form Nt = N0e^rt gives 500 × e^0.2 ≈ 611; NEET typically expects the concept — that population increases multiplicatively with r and t — rather than exact exponential arithmetic.)

Question 4

An orchid growing as an epiphyte on a mango tree, deriving support without harming or benefiting the tree, illustrates:
(a) commensalism (b) mutualism (c) parasitism (d) amensalism

Accepted Answer

(a) commensalism.

Commensalism benefits one species (+) while the other is unaffected (0) — the orchid gains support/access to light; the mango tree is neither helped nor harmed.

Question 5

Gause's Competitive Exclusion Principle states that:
(a) two species competing for the same limiting resource cannot coexist indefinitely (b) predators always eliminate their prey (c) mutualistic species always outcompete parasitic ones (d) species diversity always increases with competition

Accepted Answer

(a) two species competing for the same limiting resource cannot coexist indefinitely.

When two species have overlapping ecological niches for one limiting resource, the competitively superior species will eventually exclude the other from that habitat.

Question 6

The biomass or energy available to herbivores (primary consumers) in an ecosystem is best represented by:
(a) Net Primary Productivity (NPP) (b) Gross Primary Productivity (GPP) (c) Secondary Productivity (d) Net Secondary Productivity

Accepted Answer

(a) Net Primary Productivity (NPP).

NPP = GPP − respiration by producers; this is the actual biomass/energy remaining and available for consumption by the herbivore trophic level.

Question 7

If the producers in a grassland ecosystem fix 100,000 kcal of energy, how much energy is available to tertiary consumers (three trophic transfers from producers), assuming the standard 10% transfer efficiency?

Accepted Answer

100,000 → primary consumers: 10,000 kcal → secondary consumers: 1,000 kcal → tertiary consumers: 100 kcal.

Each trophic transfer retains only ~10% of the energy from the level below (Lindeman's 10% law); dividing by 10 three times gives 100 kcal.

Question 8

Which ecological pyramid is always upright, with no known exception in any ecosystem?
(a) pyramid of energy (b) pyramid of numbers (c) pyramid of biomass (d) all three are always upright

Accepted Answer

(a) pyramid of energy.

Because energy is lost (mostly as respiratory heat) at every trophic transfer, the energy available at a higher trophic level can never exceed that at the level below — true in every ecosystem. Numbers and biomass pyramids can be inverted (tree ecosystem; pond ecosystem, respectively).

Question 9

An inverted pyramid of biomass is typically observed in which ecosystem?
(a) a pond/aquatic ecosystem (b) a grassland ecosystem (c) a forest ecosystem (d) a desert ecosystem

Accepted Answer

(a) a pond/aquatic ecosystem.

In a pond, the standing crop biomass of phytoplankton (producers) at any instant is small compared to the biomass of zooplankton and fish that depend on them, because phytoplankton reproduce and turn over rapidly — giving an inverted biomass pyramid despite normal (upright) energy flow.

Question 10

Ecological succession that begins on a bare rock surface with no pre-existing soil is called:
(a) primary succession (b) secondary succession (c) autogenic succession only (d) allogenic succession only

Accepted Answer

(a) primary succession.

Primary succession starts on a substratum with no prior soil or organisms (e.g., bare rock, cooled lava); pioneer species like lichens must first weather the rock into soil, making this a slow process. Secondary succession, by contrast, starts where soil already exists after a disturbance and proceeds faster.

Question 11

In the species-area relationship log S = log C + Z log A, the value of Z (slope) for smaller, local areas is typically:
(a) 0.1–0.2 (b) 0.6–1.2 (c) exactly 1.0 (d) 2.0–3.0

Accepted Answer

(a) 0.1–0.2.

For relatively small areas within a region, the slope Z is fairly consistent across taxonomic groups at 0.1–0.2. For much larger areas (entire continents), Z rises to 0.6–1.2.

Question 12

Variation in the medicinal potency of Rauwolfia vomitoria growing in different Himalayan ranges is an example of:
(a) genetic diversity (b) species diversity (c) ecological diversity (d) functional diversity

Accepted Answer

(a) genetic diversity.

Genetic diversity refers to variation in genes (and gene-determined traits) within a single species across different populations or geographic ranges — here, chemical/medicinal variation within the same species.

Question 13

Depletion of the stratospheric ozone layer is primarily caused by chlorine atoms released from:
(a) chlorofluorocarbons (CFCs) (b) carbon dioxide (c) methane (d) nitrous oxide

Accepted Answer

(a) chlorofluorocarbons (CFCs).

CFCs, once widely used in refrigerants and aerosols, release chlorine atoms in the stratosphere; each chlorine atom catalytically destroys thousands of ozone molecules, forming the ozone hole (most pronounced over Antarctica). This is a distinct mechanism from CO₂-driven global warming.

Question 14

In a DDT-contaminated lake, the highest concentration of DDT accumulates in:
(a) fish-eating birds (top carnivores) (b) phytoplankton (c) zooplankton (d) small fish

Accepted Answer

(a) fish-eating birds (top carnivores).

Biomagnification progressively increases the concentration of the non-biodegradable, fat-soluble pesticide DDT at each successive trophic level, since it accumulates in fatty tissue rather than being excreted — top carnivores accumulate the highest concentration, which can cause eggshell thinning in birds of prey.

Question 15

Which of the following is NOT one of India's four recognised biodiversity hotspots?
(a) the Gangetic plains (b) the Himalaya (c) the Western Ghats and Sri Lanka (d) the Indo-Burma region

Accepted Answer

(a) the Gangetic plains.

India's four biodiversity hotspots are the Himalaya, the Western Ghats and Sri Lanka, the Indo-Burma region, and Sundaland (Nicobar Islands). The Gangetic plains, though ecologically important, is not classified as one of these hotspots.

Practice — "Ecology and Environment"

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