Organisms and Populations — Class 12 MCQs with Answers
Class 12 CBSE Biology · Chapter 11
90 practice questions · 30 Easy · 30 Medium · 30 Hard · Updated
Practise the most important Class 12 CBSE Biology questions from Chapter 11, "Organisms and Populations". You get 9 timed quizzes made from 90 NCERT-based MCQs, with answers and explanations. The questions are split into 30 Easy, 30 Medium and 30 Hard. Warm up on the basics, then move on to the exam-level questions that set top scorers in CBSE & Maharashtra HSC Board exams, MHT-CET and NEET UG apart.
To score well in "Organisms and Populations", focus on diagrams, key terms and knowing NCERT line by line. Each MCQ here is timed and uses exam-style marking (+4 correct, −1 wrong, 0 skipped). This trains you to stay accurate under time pressure, as real papers need. Every question has a short explanation, so a wrong answer becomes a quick lesson. It is the fastest way to fix gaps before a test.
Use this chapter for focused revision. Start with the Easy set to check your basics on Organisms and Populations, then move to Medium and Hard to practise applying them. Your accuracy, streaks and XP save automatically. This chapter also adds to your overall Class 12 Biology mastery score. 14 sample questions are solved in full below, with the answer and a worked explanation. Sign in free to start practising.
Key concepts: Organisms and Populations (Class 12 Biology)
Organisms and populations: how abiotic factors shape distribution and the adaptations (regulate, conform, migrate, suspend) organisms show; population attributes — density, natality, mortality, age pyramids; exponential and logistic growth; and interactions — mutualism, competition, predation, parasitism and commensalism.
- Responses to abiotic factors
- Organisms regulate (constant internal state, e.g., mammals), conform (vary with surroundings), migrate, or suspend life (hibernation, aestivation, diapause).
- Adaptations
- Kangaroo rat conserves water; desert plants use CAM and thick cuticle; Allen's and Bergmann's rules link body shape/size to cold. Acclimatisation is short-term.
- Population density
- Number of individuals per unit area or volume at a given time; may be measured relatively (pug marks, % cover) when exact counting is impractical.
- Natality and mortality
- Natality = births adding to a population; mortality = deaths. Density rises with natality + immigration and falls with mortality + emigration.
Organisms and Populations — important questions & MCQs with answers (Class 12 Biology)
14 solved questions from this chapter's difficulty levels, each with its answer and explanation. The other 76 are timed and scored when you sign in.
- Q1Easy
Both species benefit:
A.PredationB.Mutualism (+/+)✓ CorrectC.ParasitismD.CompetitionAnswer: B. Mutualism (+/+)
Explanation: Mutualism is the +/+ interaction — both partners gain, as bees do collecting nectar while pollinating flowers; confusing it with commensalism (+/0), where only one side benefits, is the common slip.
- Q2Easy
Exponential growth occurs when:
A.AlwaysB.Resources are scarceC.Population is stableD.Resources are unlimited✓ CorrectAnswer: D. Resources are unlimited
Explanation: Exponential growth needs unlimited food, space and no predators, producing an unchecked J-shaped curve; real populations rarely sustain this once resources start becoming limiting.
- Q3Easy
Ecology at the organismic level chiefly deals with:
A.Energy flow in ecosystemsB.How organisms are adapted to their environment✓ CorrectC.Global carbon cyclesD.Population growth onlyAnswer: B. How organisms are adapted to their environment
Explanation: Organismic (organism-level) ecology studies how an individual's physiology, morphology and behaviour let it survive and reproduce under abiotic stress — energy flow and carbon cycling belong to ecosystem-level ecology instead.
- Q4Easy
Population density is best defined as the number of individuals:
A.That dieB.Born per yearC.Per unit area or volume✓ CorrectD.That migrateAnswer: C. Per unit area or volume
Explanation: Population density is the number of individuals of a species per unit area or volume at a given time — a snapshot count, not a rate like births or deaths, which instead describe how density changes.
- Q5Easy
Which is the most important abiotic factor governing the distribution of organisms?
A.ColourB.SoundC.MagnetismD.Temperature✓ CorrectAnswer: D. Temperature
Explanation: Temperature is the single most important abiotic factor shaping species distribution because it drives enzyme kinetics and metabolic rate — most organisms function only within a defined temperature range.
- Q6Easy
Natality refers to the number of:
A.EmigrantsB.DeathsC.ImmigrantsD.Births in a population✓ CorrectAnswer: D. Births in a population
Explanation: Natality is the number of births added to a population over a given period; mortality is the parallel count of deaths — together with immigration and emigration these set whether a population grows or shrinks.
- Q7Medium
Commensalism (+/0):
A.One benefits, other unaffected✓ CorrectB.Both benefitC.Both harmedD.None affectedAnswer: A. One benefits, other unaffected
Explanation: Commensalism (+/0) benefits one partner while the other is neither helped nor harmed, e.g. barnacles riding on a whale for transport; mixing this up with mutualism, where both sides gain, is the classic trap.
- Q8Medium
Logistic growth has:
A.J-shapedB.S-shaped (sigmoid) curve with carrying capacity✓ CorrectC.LinearD.RandomAnswer: B. S-shaped (sigmoid) curve with carrying capacity
Explanation: Logistic growth follows dN/dt = rN(K−N)/K, giving an S-shaped (sigmoid) curve that flattens as N nears carrying capacity K — unlike unlimited exponential growth's J-shaped curve, which never levels off.
- Q9Medium
Gause's competitive exclusion principle states that two competing species:
A.Never competeB.Always coexistC.Cannot coexist indefinitely on identical limited resources✓ CorrectD.Both go extinctAnswer: C. Cannot coexist indefinitely on identical limited resources
Explanation: Gause's competitive exclusion principle states that two species competing for the exact same limiting resource within an identical niche cannot coexist indefinitely — the more efficient one drives the other out.
- Q10Medium
In exponential growth dN/dt = rN, 'r' represents the:
A.Population densityB.Carrying capacityC.Death rate onlyD.Intrinsic rate of natural increase✓ CorrectAnswer: D. Intrinsic rate of natural increase
Explanation: In the exponential growth equation dN/dt = rN, N is population size and r is the intrinsic rate of natural increase — birth rate minus death rate — not the carrying capacity, which only appears in the logistic model.
- Q11Medium
Competing species can coexist by resource partitioning, which MacArthur showed in:
A.Avoiding all foodB.Identical feeding habitsC.Sharing one food source equallyD.Warblers feeding in different zones of the same tree✓ CorrectAnswer: D. Warblers feeding in different zones of the same tree
Explanation: MacArthur showed that competing warbler species avoid direct competition through resource partitioning — each forages in a different zone of the same tree — reducing the pressure that would otherwise exclude one species.
- Q12Hard
Gause's competitive exclusion principle:
A.NoneB.All species share resources equallyC.Predators always winD.Two species with identical niches cannot coexist indefinitely✓ CorrectAnswer: D. Two species with identical niches cannot coexist indefinitely
Explanation: Gause's competitive exclusion principle holds that two species competing for the same limiting resource in an identical niche cannot coexist indefinitely — the more efficient competitor eventually eliminates the other.
- Q13Hard
Behavioural adaptation:
A.Body shape onlyB.Permanent thick furC.Hibernation in winter✓ CorrectD.Colour blueAnswer: C. Hibernation in winter
Explanation: Hibernation is a behavioural adaptation — the animal actively lowers activity and metabolic rate to conserve energy through winter cold, unlike a permanent thick coat, which is a fixed structural adaptation, not a behaviour.
- Q14Hard
Assertion: Predators should not be too efficient at killing prey. Reason: An over-efficient predator could drive the prey to extinction and then starve itself. Choose the correct option.
A.Both true, reason does not explainB.Both true and reason explains assertion✓ CorrectC.Assertion true, reason falseD.Both falseAnswer: B. Both true and reason explains assertion
Explanation: An over-efficient predator that eliminates its entire prey population removes its own food source and starves — stable predator-prey systems favour predators that don't drive prey to extinction, which is exactly what the reason explains.
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Start this chapter free →Organisms and Populations — FAQs
What are the key concepts in Class 12 Biology Organisms and Populations?+
Organisms and populations: how abiotic factors shape distribution and the adaptations (regulate, conform, migrate, suspend) organisms show; population attributes — density, natality, mortality, age pyramids; exponential and logistic growth; and interactions — mutualism, competition, predation, parasitism and commensalism. Key ideas include Responses to abiotic factors, Adaptations, Population density, Natality and mortality.
What does Class 12 Biology Chapter 11 (Organisms and Populations) cover on XamBaaz?+
It has 90 NCERT-based MCQs on "Organisms and Populations": 30 Easy, 30 Medium and 30 Hard. Together they make 9 timed quizzes, and you never get the same set twice. Every question has an instant explanation. They help you prepare for CBSE & Maharashtra HSC Board exams, MHT-CET and NEET UG.
Are these "Organisms and Populations" questions free to practise?+
Yes. Sign in with Google to practise "Organisms and Populations" free. Full unlimited access is ₹999/year on a launch offer until 1 December 2026. No chapter is charged separately.
How should I revise "Organisms and Populations" for the exam?+
Start with the Easy quiz to check your basics, then try Medium and Hard to practise applying them. There are 9 timed quizzes on this chapter, so you can come back for a fresh set instead of one you have seen. Read each explanation, retry the questions you miss, and track your accuracy until it stays high.
Are these "Organisms and Populations" MCQs available with answers?+
Yes. 14 sample questions are shown here in full, each with the correct option and a step-by-step "Why" explanation. Sign in free with Google to start practising, with instant scoring.
Is there negative marking in the "Organisms and Populations" quizzes?+
Yes. The timed quizzes use exam-style marking: +4 for a right answer, −1 for a wrong one and 0 for a skip, the same negative marking as NEET UG. MHT-CET and CBSE board papers have no negative marking. Our mocks for those are scored their way.
What are the important questions from Organisms and Populations (Class 12 Biology)?+
The questions that matter most test Responses to abiotic factors, Adaptations, Population density, Natality and mortality. This page shows 14 solved important MCQs with answers and explanations; all 90 questions on the chapter are available as timed quizzes once you sign in.
Is there an online quiz for Organisms and Populations?+
Yes — Class 12 Biology Organisms and Populations has timed online quizzes at Easy, Medium and Hard levels, with instant scoring and a worked explanation on every question. The first quiz on the chapter is free.