Organisms and Populations — NEET Zoology MCQs with answers

Organisms and Populations is a Class 12 Zoology chapter in the NEET (UG) syllabus. NEET720 has 263 reviewed practice questions on it, each with a quick answer and a step-by-step explanation. The 8 questions below are free and fixed, so you can bookmark this page; the full chapter, plus mistake tracking and spaced revision, is in the app.

Topics covered

Life History Strategies · Survivorship · Population Growth · Population Regulation · Population attributes · Population interactions · Animal adaptations · Animal behaviour · Organismic adaptation · Organism and Its Environment · Population Attributes and Growth

8 free Organisms and Populations practice questions with answers

Choose an answer in your head before opening it. Each explanation says why the correct option is right and, where relevant, why the tempting wrong option is wrong.

1. Question 1 · medium · Population attributes

   How many of the following statements about population growth curves are correct? (I) The J-shaped growth curve represents exponential growth, occurring when resources are unlimited. (II) The S-shaped (sigmoid) growth curve represents logistic growth, occurring when resources become limiting as population size approaches carrying capacity. (III) In logistic growth, population growth rate is maximum exactly at carrying capacity (K). (IV) Most natural animal populations tend to follow the logistic model more closely than the exponential model over the long term, due to finite resources.

   • A.One
   • B.Two
   • C.Three
   • D.Four
   Show answer and explanation

   Answer: C. Three

   I, II, IV correct; in logistic growth, the growth rate is maximum at K/2, not at carrying capacity K itself, where growth rate approaches zero.

   Exponential (J-shaped) growth occurs with unlimited resources, while logistic (S-shaped) growth reflects resource limitation as population approaches carrying capacity (K), with growth rate slowing as resources become scarce. In the logistic model, the population growth rate is actually maximum at an intermediate population size (K/2) and approaches zero as the population nears K, not maximum at K itself as falsely stated. Most natural populations, being resource-limited, tend to follow logistic growth patterns more closely over time.

   Common mistake: Assuming growth rate is maximum at carrying capacity rather than at an intermediate population size

2. Question 2 · hard · Population attributes

   A population of insects has an initial size of 200 individuals and an intrinsic rate of natural increase (r) leading to a growth rate such that the population doubles every 10 days under exponential growth assumptions. Approximately what would the population size be after 20 days?

   • A.800
   • B.400
   • C.1600
   • D.600
   Show answer and explanation

   Answer: A. 800

   With doubling every 10 days, in 20 days there are 2 doubling periods: 200 → 400 → 800.

   Since the population doubles every 10 days, in 20 days there are two complete doubling periods. Starting at 200: after the first 10 days, population = 200 × 2 = 400; after the second 10 days, population = 400 × 2 = 800.

   Common mistake: Miscounting the number of doubling periods within the given time frame

3. Question 3 · medium · Population attributes

   How many of the following statements about population age pyramids are correct? (I) A broad-based, triangular pyramid (many pre-reproductive individuals) typically indicates an expanding/growing population. (II) A bell-shaped, more uniform pyramid typically indicates a relatively stable population. (III) An urn-shaped pyramid, narrower at the base, typically indicates a declining population. (IV) Age pyramid shape provides no useful information about future population trends.

   • A.One
   • B.Two
   • C.Three
   • D.Four
   Show answer and explanation

   Answer: C. Three

   I, II, III correct; age pyramids are actually a useful tool for predicting future population trends, contrary to statement IV.

   A broad-based (triangular) age pyramid, with many pre-reproductive individuals, suggests an expanding population. A bell-shaped, relatively uniform pyramid suggests a stable population. An urn-shaped pyramid, narrower at the base, suggests a declining population, since fewer young individuals are present to replace the older generation. Age pyramid shape is indeed a valuable demographic tool for predicting future population trends, contradicting statement IV.

   Common mistake: Underestimating the predictive value of age pyramid shape for future population trends

4. Question 4 · medium · Population interactions

   Match the interspecific interaction type with its effect on the two interacting species (species A, species B): Column I: (A) Mutualism (B) Commensalism (C) Parasitism (D) Amensalism Column II: (1) A benefits, B is harmed (2) A benefits, B unaffected (3) A benefits, B benefits (4) A is harmed/unaffected, B is harmed (with no benefit to A)

   • A.A-3, B-2, C-1, D-4
   • B.A-2, B-3, C-1, D-4
   • C.A-3, B-1, C-2, D-4
   • D.A-3, B-2, C-4, D-1
   Show answer and explanation

   Answer: A. A-3, B-2, C-1, D-4

   Mutualism: both benefit; commensalism: one benefits, other unaffected; parasitism: one benefits, other harmed; amensalism: one harmed, other unaffected/no benefit.

   Mutualism benefits both interacting species (e.g., pollinators and flowering plants). Commensalism benefits one species while the other is unaffected (e.g., cattle egrets and cattle). Parasitism benefits one species (the parasite) while harming the other (the host). Amensalism harms one species while the other is largely unaffected and gains no benefit, distinguishing it from parasitism where the unaffected party actually benefits.

   Common mistake: Confusing amensalism (no benefit to the unaffected/causing party) with parasitism (clear benefit to the parasite)

5. Question 5 · hard · Population interactions

   In classic predator-prey population cycles (e.g., lynx and snowshoe hare), the predator population peak typically:

   • A.Lags slightly behind the prey population peak, since predator numbers increase in response to prior high prey availability
   • B.Occurs simultaneously and in perfect synchrony with the prey population peak at all times
   • C.Always precedes the prey population peak by a fixed, predictable interval
   • D.Shows no relationship whatsoever to prey population fluctuations
   Show answer and explanation

   Answer: A. Lags slightly behind the prey population peak, since predator numbers increase in response to prior high prey availability

   Predator population peaks typically lag behind prey population peaks, reflecting a delayed numerical response to prey abundance.

   In classic predator-prey cycles, an increase in prey population provides more food resources, which after a time lag (reflecting reproduction and growth time) leads to an increase in predator population. As predators increase, they exert greater pressure on prey, eventually causing prey decline, followed later by predator decline due to reduced food availability, creating the characteristic lagged, cyclical pattern observed in classic studies like lynx-hare population data.

   Common mistake: Assuming predator and prey population peaks occur in perfect synchrony rather than with a time lag

6. Question 6 · hard · Population interactions

   The competitive exclusion principle (Gause's principle) states that:

   • A.Two species competing for exactly the same limiting resource/niche cannot indefinitely coexist in the same habitat; one will eventually outcompete and exclude the other
   • B.Any two species occupying the same habitat will always coexist indefinitely, regardless of niche overlap
   • C.Competition only ever occurs between individuals of the same species, never between different species
   • D.Species occupying completely different niches will always experience intense competitive exclusion
   Show answer and explanation

   Answer: A. Two species competing for exactly the same limiting resource/niche cannot indefinitely coexist in the same habitat; one will eventually outcompete and exclude the other

   Gause's competitive exclusion principle states that two species with identical resource requirements cannot indefinitely coexist; one will outcompete the other.

   The competitive exclusion principle, based on experiments by G.F. Gause with Paramecium species, states that when two species compete for exactly the same limiting resource(s)/niche, they cannot stably coexist indefinitely; the more efficient competitor will eventually exclude the other from that habitat, unless niche differentiation (resource partitioning) reduces direct competition between them.

   Common mistake: Confusing competitive exclusion's applicability to complete niche overlap with general co-occurrence of any two species

7. Question 7 · medium · Animal adaptations

   How many of the following statements correctly describe animal thermoregulation strategies? (I) Endotherms (e.g., mammals, birds) generate substantial metabolic heat internally to maintain a relatively stable body temperature regardless of ambient temperature within limits. (II) Ectotherms (e.g., most reptiles, amphibians, fish) rely predominantly on external heat sources, with body temperature fluctuating with the environment. (III) Behavioural thermoregulation, such as basking in the sun or seeking shade, is commonly used by ectotherms to help regulate body temperature. (IV) Endothermy is always metabolically 'cheaper' (requires less energy) than ectothermy under all environmental conditions.

   • A.One
   • B.Two
   • C.Three
   • D.Four
   Show answer and explanation

   Answer: C. Three

   I, II, III correct; endothermy is actually more energetically costly than ectothermy due to continuous internal heat generation, not cheaper.

   Endotherms maintain relatively stable body temperature through internal metabolic heat generation, while ectotherms rely on external heat sources, with body temperature fluctuating accordingly; ectotherms often use behavioural thermoregulation like basking to help manage temperature. However, endothermy demands considerably more continuous energy expenditure to sustain internal heat production compared to ectothermy, making the claim in statement IV that endothermy is always metabolically cheaper incorrect.

   Common mistake: Assuming endothermy is always the more energy-efficient thermoregulation strategy

8. Question 8 · medium · Animal adaptations

   Hibernation, a physiological adaptation seen in certain mammals during winter, primarily helps the animal survive periods of:

   • A.Extreme cold and scarce food availability, by drastically reducing metabolic rate and body temperature to conserve energy
   • B.Excessive heat and drought, by drastically increasing metabolic rate to dissipate heat
   • C.Excess food abundance, by increasing activity levels to consume surplus resources
   • D.Breeding season stress exclusively, unrelated to any seasonal temperature or food changes
   Show answer and explanation

   Answer: A. Extreme cold and scarce food availability, by drastically reducing metabolic rate and body temperature to conserve energy

   Hibernation helps mammals survive winter's cold and scarce food by drastically lowering metabolic rate and body temperature.

   Hibernation is a physiological state some mammals (e.g., certain bears, ground squirrels) enter during winter, characterised by drastically reduced metabolic rate, lowered body temperature, and decreased heart/respiratory rate, allowing the animal to conserve energy and survive extended periods of cold temperatures and scarce food availability without needing to actively forage.

   Common mistake: Confusing hibernation (cold/winter response) with estivation (heat/drought response)

Questions about Organisms and Populations for NEET

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Questions are original NEET720 compositions reviewed for correctness, syllabus fit and option quality. Counts update as the bank grows (263 active practice questions in this chapter today).