Biodiversity loss is accelerating globally, and NEET consistently tests whether you can distinguish the causes, quantify the relationship between habitat area and species richness, and match conservation strategies to their correct categories.
The species-area relationship (Alexander von Humboldt's observation, formalized by Arrhenius) states: log S = log C + Z log A. The slope Z ranges 0.1–0.2 for small regions within a continent, but steepens to 0.6–1.2 when the analysis spans entire continents. NEET questions frequently test whether you remember which Z-range applies where — confusing the two is a high-frequency error.
Causes of biodiversity loss — the "Evil Quartet" (Edward Wilson): habitat loss and fragmentation, over-exploitation, alien species invasions, and co-extinctions. Habitat loss is the most potent driver. The Amazon rainforest ("lungs of the planet") is being cut for soybean cultivation and cattle ranching. When a habitat is reduced to a fraction, the species-area curve predicts how many species will be lost.
Conservation strategies split into two categories:
A common NEET distractor places sacred groves under ex-situ or confuses biodiversity hotspots with biosphere reserves. Hotspots are biogeographic zones identified by high endemism and high threat (Norman Myers); biosphere reserves are administratively designated protected areas.
Biodiversity hotspots require two criteria: ≥1500 endemic vascular plant species AND ≥70% habitat loss. Three of them cover India: Western Ghats & Sri Lanka, Indo-Burma, and Himalaya. NCERT Class 12 Biology Chapter 13, page 224, documents these as core evaluable facts.
The IUCN Red List: NCERT anchors the scale of biodiversity loss with the IUCN's own records: the IUCN Red List (2004) documents the extinction of 784 species over the last 500 years, made up of 338 vertebrates, 359 invertebrates, and 87 plants (NCERT Class 12 Biology, Chapter 13, page 221). The Red List is compiled by the International Union for Conservation of Nature and Natural Resources (IUCN) — the same body NCERT cites when noting that just over 1.5 million plant and animal species have been described so far, out of an unknown, much larger total still to be discovered. For NEET, remember the Red List as the running extinction record the IUCN maintains, distinct from India's own protected-area categories like biosphere reserves and national parks.
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
Which of the following is NOT one of Edward Wilson's "Evil Quartet" causes of biodiversity loss?
Answer: D. The Evil Quartet (Edward Wilson) comprises habitat loss and fragmentation, over-exploitation, alien species invasions, and co-extinctions. Global warming is a significant threat to biodiversity but is not part of this specific classification from NCERT Class 12 Biology Chapter 13.
Why A is wrong: A is wrong because habitat loss and fragmentation is the FIRST and most potent of the Evil Quartet — it cannot be excluded.
Why B is wrong: B is wrong because over-exploitation (hunting, poaching, over-harvesting) is explicitly the second member of the Evil Quartet.
Why C is wrong: C is wrong because alien species invasions (e.g., Nile perch in Lake Victoria, water hyacinth in Indian water bodies) is the third member of the Evil Quartet.
How many biodiversity hotspots are currently recognized in India?
Answer: B. B is correct. NCERT states plainly that three of the world's biodiversity hotspots cover India's regions of exceptionally high biodiversity: Western Ghats and Sri Lanka, Indo-Burma, and Himalaya. Learn them as a set of three named regions rather than as a number, because the count is what gets misremembered (NCERT Class 12 Biology Chapter 13, page 224).
Why A is wrong: A is wrong because 2 is too few — it usually comes from recalling only the Western Ghats and the Himalaya and forgetting Indo-Burma.
Why C is wrong: C is wrong because 4 comes from adding Sundaland to the list. Sundaland is a genuine global hotspot, but NCERT does not count it among those covering India — the book names exactly three.
Why D is wrong: D is wrong because 5 overcounts. NCERT names three, and no further hotspot is listed as covering India.
Which of the following is an example of ex-situ conservation?
Answer: A. Cryopreservation in seed banks conserves genetic material outside the organism's natural habitat — the definition of ex-situ conservation. Biosphere reserves, sacred groves, and national parks are all in-situ strategies (NCERT Class 12 Biology Chapter 13).
Why B is wrong: B is wrong because sacred groves are traditional in-situ conservation sites where communities protect patches of forest for cultural or religious reasons.
Why C is wrong: C is wrong because biosphere reserves protect organisms within their natural ecosystem — this is in-situ conservation by definition.
Why D is wrong: D is wrong because national parks are designated in-situ protected areas where wild animals are conserved in their natural habitat.
In the species-area relationship log S = log C + Z log A, a researcher plotting bird species richness against area across a series of study regions obtains a regression slope Z = 0.75. What can be inferred about the geographic scope of that analysis?
Answer: D. For small regions within a continent, Z ranges 0.1–0.2. Values of 0.6–1.2 are observed when the species-area relationship is applied across continents or very large areas. Z = 0.75 falls in the latter range, indicating the comparison is effectively at a continental scale (NCERT Class 12 Biology Chapter 13).
Why A is wrong: A is wrong because typical Z for small intra-continental regions is 0.1–0.2; 0.75 far exceeds this range.
Why B is wrong: B is wrong because Z is the slope of the species-area curve, not a measure of species loss per se; a steeper Z means species richness is more sensitive to area changes.
Why C is wrong: C is wrong because the relationship remains valid — the Arrhenius equation applies across scales; only the Z value changes depending on the geographic scope.
A biodiversity hotspot must satisfy two criteria for designation. Which combination is correct?
Answer: C. Norman Myers' criteria require a region to harbour at least 1,500 species of endemic vascular plants AND to have lost at least 70% of its original habitat to qualify as a biodiversity hotspot (NCERT Class 12 Biology Chapter 13).
Why A is wrong: A is wrong because it lowers both thresholds — the correct numbers are 1,500 endemic vascular plants and 70% habitat loss, not 1,000 and 50%.
Why B is wrong: B is wrong because the criterion specifies endemic vascular PLANTS (not animals), and the habitat-loss threshold is 70% (not 80%).
Why D is wrong: D is wrong because the criterion is specifically about vascular plants (not a combined plant + animal count), and the threshold is 1,500 endemic species with 70% loss.
If a tropical forest of area A is reduced to 10% of its original area, and the species-area slope Z = 0.2, approximately what percentage of species would be predicted to survive?
Answer: B. Using S = CA^Z: if area becomes 0.1A, then new S/original S = (0.1A)^Z / A^Z = (0.1)^0.2 = 10^(−0.2) ≈ 0.631. About 63% of species survive, meaning roughly 37% are lost. This is a standard NEET application of the species-area relationship (NCERT Class 12 Biology Chapter 13).
Why A is wrong: A is wrong because this assumes a linear relationship (10% area → 10% species) — the power-law relationship with Z = 0.2 buffers species loss, so far more than 10% survive.
Why C is wrong: C is wrong because 50% survival would require a much greater area loss or a higher Z value; with Z = 0.2 and 10% area remaining, the calculation gives ~63%.
Why D is wrong: D is wrong because 90% survival implies negligible species loss with 90% habitat destruction — the species-area curve always predicts measurable loss when area decreases this dramatically.
Sacred groves are considered effective biodiversity conservation sites because they:
Answer: A. Sacred groves are tracts of forest protected by local communities due to religious or cultural beliefs. They function as refugia for rare species because exploitation (cutting trees, hunting) is taboo. They are in-situ, community-driven, and pre-date formal legislation (NCERT Class 12 Biology Chapter 13).
Why B is wrong: B is wrong because sacred groves are in-situ (not ex-situ) conservation and are maintained by communities based on tradition, not government funding.
Why C is wrong: C is wrong because zoological parks are ex-situ facilities with active breeding programs; sacred groves are passive in-situ protection through non-interference.
Why D is wrong: D is wrong because sacred groves are traditional community institutions that predate modern legislation; they were not 'established' by the Wildlife Protection Act.
An island originally has 500 species and an area of 10,000 km². After deforestation, 90% of the area is lost. Using the species-area relationship with Z = 0.2, how many species are estimated to be lost?
Answer: B. Remaining area = 10% of original = 1,000 km². Species remaining: S_new/S_old = (A_new/A_old)^Z = (0.1)^0.2 = 10^(−0.2) ≈ 0.631. Species remaining ≈ 500 × 0.631 ≈ 315. Species LOST = 500 − 315 = 185 (NCERT Class 12 Biology Chapter 13, species-area relationship application).
Why A is wrong: A is wrong because 50 assumes only 10% species loss (same percentage as the area fraction remaining) — this ignores the Z-exponent buffering in the power-law relationship.
Why C is wrong: C is wrong because 315 is the number of species REMAINING, not species lost. The question asks for species lost: 500 − 315 = 185.
Why D is wrong: D is wrong because 450 species lost (90% of 500) assumes a linear 1:1 relationship between area loss and species loss, ignoring the Z = 0.2 power-law exponent.
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Pattern: Species-area relationship application (from P.BIO.U10.UNIT_BUNDLE — recall + direct_application)
Given
• Original area: A₁ = 50,000 km²• Reduced area: A₂ = 5,000 km² (90% habitat loss)• Original species count: S₁ = 2,000• Z = 0.2 (intra-continental region)• C is constant for both calculations
Required
Number of species predicted to survive after habitat loss, and the number lost.
Concept
The Arrhenius species-area relationship: log S = log C + Z log A. When comparing two areas in the same region, C cancels out, giving S₂/S₁ = (A₂/A₁)^Z.
Formula
S₂/S₁ = (A₂/A₁)^Z
Substitution
S₂/2000 = (5000/50000)^0.2 = (0.1)^0.2
Calculation
(0.1)^0.2 = 10^(−0.2) = antilog(−0.2) ≈ 0.631
S₂ = 2000 × 0.631 = 1262 species survive
Species lost = 2000 − 1262 = 738
Note: 2000 (original species count) and 0.2 (given Z value) are problem-defined exact values and do not introduce rounding uncertainty into significant figures.
Final answer
Approximately 1,262 species survive; approximately 738 species are predicted to be lost.
Common trap
Students often assume that 90% area loss means 90% species loss (i.e., 1,800 lost). The power-law relationship with Z = 0.2 buffers the loss — actual predicted loss is ~37%, not 90%. Another trap: confusing "species remaining" with "species lost" (315 vs 185 in the MCQ above).
Similar NEET-style question
"A tropical region has 1,500 plant species in an area of 20,000 km². If the area is reduced to 2,000 km², estimate the number of plant species likely to survive (Z = 0.2)." [Answer: S₂ = S₁ × (A₂/A₁)^Z = 1500 × (2000/20000)^0.2 = 1500 × 0.1^0.2 = 1500 × 0.63096 = 946.4 ≈ 946 species. Carry the factor to five figures before multiplying: truncating 0.63096 to 0.631 gives 946.5, which then rounds the wrong way to 947.]
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In situ: national parks, biosphere reserves (e.g. Nilgiri, Sundarbans), sacred groves. Ex situ: zoos, botanical gardens, gene banks, cryopreservation. IUCN Red List: extinct, EW, CR, EN, VU, NT, LC, DD, NE.
-- NCERT Class 12 Biology, Chapter 13, p. 224More in Ecology and Environment: 3 exam traps and mistakes · 3 formulas · 1 question pattern from its other lessons.
10 questions from NEET 2022, 2023, 2024, 2025. Answers verified against NTA official keys.
Which one of the following is an example of ex-situ conservation?
List of endangered species was released by-
Which of the following is not a method of ex situ conservation?
In-situ conservation refers to:
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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