CBSE Class 12 Biology MCQs – Organisms and Populations (NCERT Based)

Unit V: Ecology and Environment | Chapter 13: Organisms and Populations

CBSE Class 12 Biology Chapter 13 MCQs with Answers and Explanations – Organisms and Populations (NCERT)

Course & Examination Details

• Course: CBSE Class 12 Biology
• Unit: Unit V – Ecology and Environment
• Chapter: Chapter 13 – Organisms and Populations
• Board: Central Board of Secondary Education (CBSE)
• Syllabus Base: Strictly as per NCERT Textbook
• Exam Relevance: CBSE Class 12 Board Exams, School Tests, Competitive Exam Foundation

Multiple Choice Questions (MCQs) with Answers & Explanations

(50 MCQs prepared strictly according to NCERT concepts with detailed, concept-clearing explanations)

Section A: Organism and Environment (Q1–Q8)

Q1. Ecology is the study of:
A. Structure of cells
B. Heredity and variation
C. Interactions among organisms and environment
D. Classification of organisms

Correct Answer: C
Explanation: Ecology deals with interactions among organisms and between organisms and their physical environment, not with cellular or genetic processes.

Q2. Which level of ecological organization comes immediately above population?
A. Organism
B. Community
C. Ecosystem
D. Biome

Correct Answer: B
Explanation: A community consists of interacting populations of different species living in the same area.

Q3. Organisms are called open systems because they:
A. Do not respire
B. Exchange energy and matter
C. Are isolated from environment
D. Do not interact

Correct Answer: B
Explanation: Organisms continuously exchange matter and energy with their surroundings, making them open systems.

Q4. Environmental stress is caused when:
A. Resources are abundant
B. Conditions remain constant
C. Factors exceed tolerance limits
D. Organisms migrate

Correct Answer: C
Explanation: Environmental stress occurs when abiotic factors exceed the tolerance limits of organisms.

Q5. Which factor does NOT directly affect organism distribution?
A. Temperature
B. Water
C. Soil
D. Taxonomy

Correct Answer: D
Explanation: Taxonomy deals with classification, not environmental distribution.

Q6. Which of the following best defines habitat?
A. Role of organism
B. Physical place of living
C. Trophic level
D. Interaction pattern

Correct Answer: B
Explanation: Habitat refers to the physical place where an organism lives and grows.

Q7. Which term describes the functional role of an organism?
A. Habitat
B. Community
C. Niche
D. Population

Correct Answer: C
Explanation: Niche describes how an organism lives, feeds, and interacts in its environment.

Q8. Ecology helps in understanding:
A. Protein synthesis
B. Ecosystem stability
C. DNA replication
D. Cell division

Correct Answer: B
Explanation: Ecology explains interactions, population dynamics, and ecosystem balance.

Section B: Major Abiotic Factors (Q9–Q18)

Q9. The most ecologically relevant abiotic factor is:
A. Light
B. Water
C. Temperature
D. Soil

Correct Answer: C
Explanation: Temperature directly affects enzyme activity, metabolism, and survival.

Q10. Organisms tolerating wide temperature ranges are called:
A. Stenothermal
B. Eurythermal
C. Endothermic
D. Ectothermic

Correct Answer: B
Explanation: Eurythermal organisms survive over a wide range of temperatures.

Q11. Which plant type is adapted to dry conditions?
A. Hydrophyte
B. Mesophyte
C. Xerophyte
D. Halophyte

Correct Answer: C
Explanation: Xerophytes are adapted to arid environments with low water availability.

Q12. Light is essential for plants mainly because it is required for:
A. Respiration
B. Transpiration
C. Photosynthesis
D. Germination

Correct Answer: C
Explanation: Light provides energy for photosynthesis.

Q13. Salinity mainly affects organisms by disturbing:
A. Respiration
B. Osmotic balance
C. Nutrition
D. Reproduction

Correct Answer: B
Explanation: High salinity disrupts osmotic balance in organisms.

Q14. Soil influences vegetation through all EXCEPT:
A. Texture
B. pH
C. Mineral content
D. Latitude

Correct Answer: D
Explanation: Latitude is a climatic factor, not a soil property.

Q15. Freshwater organisms are usually:
A. Euryhaline
B. Stenohaline
C. Eurythermal
D. Conformers

Correct Answer: B
Explanation: Freshwater organisms cannot tolerate wide salinity changes.

Q16. Light penetration in aquatic ecosystems decreases with:
A. Depth
B. Salinity
C. Temperature
D. pH

Correct Answer: A
Explanation: Light is absorbed and scattered with increasing depth.

Q17. Abiotic factors are called limiting factors because they:
A. Enhance growth
B. Restrict survival
C. Promote migration
D. Increase diversity

Correct Answer: B
Explanation: When beyond tolerance limits, abiotic factors restrict survival.

Q18. Which abiotic factor indirectly affects animals by influencing plants?
A. Light
B. Soil
C. Temperature
D. Water

Correct Answer: B
Explanation: Soil determines vegetation, which supports animal life.

Section C: Responses to Abiotic Factors (Q19–Q28)

Q19. Maintenance of constant internal environment is called:
A. Conformation
B. Migration
C. Regulation
D. Suspension

Correct Answer: C
Explanation: Regulation maintains homeostasis despite environmental changes.

Q20. Birds and mammals are examples of:
A. Conformers
B. Regulators
C. Migrators
D. Suspenders

Correct Answer: B
Explanation: They regulate body temperature and internal conditions.

Q21. Most plants are:
A. Regulators
B. Migratory
C. Conformers
D. Homeotherms

Correct Answer: C
Explanation: Plants cannot regulate internal conditions actively.

Q22. Seasonal movement of organisms is called:
A. Regulation
B. Migration
C. Aestivation
D. Hibernation

Correct Answer: B
Explanation: Migration helps avoid unfavorable conditions.

Q23. Hibernation and aestivation are examples of:
A. Regulation
B. Conformation
C. Suspension
D. Migration

Correct Answer: C
Explanation: Suspension reduces metabolic activity during stress.

Q24. Diapause occurs mainly in:
A. Birds
B. Mammals
C. Insects
D. Fishes

Correct Answer: C
Explanation: Diapause is common in insects during unfavorable conditions.

Q25. Regulation is energetically expensive because it involves:
A. Reduced metabolism
B. Continuous energy use
C. Seasonal movement
D. Structural change

Correct Answer: B
Explanation: Constant physiological adjustments consume energy.

Q26. Conformers are usually restricted to:
A. Stable environments
B. Extreme climates
C. All habitats
D. Polar regions

Correct Answer: A
Explanation: Conformers survive where conditions do not fluctuate widely.

Q27. Migration mainly helps organisms to:
A. Compete
B. Adapt genetically
C. Escape stress
D. Regulate body temperature

Correct Answer: C
Explanation: Migration avoids unfavorable environmental conditions.

Q28. Which response allows survival without migration or regulation?
A. Conformation
B. Suspension
C. Adaptation
D. Competition

Correct Answer: B
Explanation: Suspension helps survive harsh periods by lowering metabolism.

Section D: Adaptations (Q29–Q38)

Q29. Adaptations are:
A. Temporary changes
B. Learned behaviors
C. Inherited traits
D. Random responses

Correct Answer: C
Explanation: Adaptations are genetically inherited over generations.

Q30. CAM pathway is an adaptation to:
A. Low temperature
B. Low oxygen
C. Water scarcity
D. High salinity

Correct Answer: C
Explanation: CAM plants reduce water loss in arid conditions.

Q31. Streamlined body in fish helps in:
A. Respiration
B. Feeding
C. Reducing resistance
D. Reproduction

Correct Answer: C
Explanation: Streamlining reduces friction during swimming.

Q32. Thick fur in polar animals helps in:
A. Protection
B. Insulation
C. Feeding
D. Communication

Correct Answer: B
Explanation: Thick fur reduces heat loss in cold climates.

Q33. Increased RBC count in high-altitude humans is a:
A. Behavioral adaptation
B. Morphological adaptation
C. Physiological adaptation
D. Genetic disorder

Correct Answer: C
Explanation: It improves oxygen transport in low-oxygen environments.

Q34. Which adaptation reduces transpiration in plants?
A. Broad leaves
B. Thin cuticle
C. Reduced leaves
D. Soft stems

Correct Answer: C
Explanation: Reduced leaves minimize water loss.

Q35. Gills are adaptations for:
A. Movement
B. Respiration
C. Feeding
D. Buoyancy

Correct Answer: B
Explanation: Gills extract dissolved oxygen from water.

Q36. Adaptations mainly increase:
A. Population size
B. Survival and reproduction
C. Competition
D. Migration

Correct Answer: B
Explanation: Adaptations enhance fitness in a given environment.

Q37. Which is NOT an aquatic adaptation?
A. Streamlined body
B. Gills
C. Fins
D. Thick cuticle

Correct Answer: D
Explanation: Thick cuticle is a desert plant adaptation.

Q38. Adaptations evolve due to:
A. Mutation alone
B. Natural selection
C. Migration
D. Regulation

Correct Answer: B
Explanation: Natural selection favors beneficial traits over generations.

Section E: Population Attributes, Growth & Interactions (Q39–Q50)

Q39. A group of same species in a given area is called:
A. Community
B. Ecosystem
C. Population
D. Biome

Correct Answer: C
Explanation: Population includes individuals of the same species.

Q40. Population density can be measured by all EXCEPT:
A. Number
B. Biomass
C. Percent cover
D. Age

Correct Answer: D
Explanation: Age is a population attribute, not a density measure.

Q41. Natality refers to:
A. Death rate
B. Birth rate
C. Migration rate
D. Growth rate

Correct Answer: B
Explanation: Natality is the rate of birth in a population.

Q42. An expanding age pyramid indicates:
A. Stable population
B. Declining population
C. Growing population
D. Extinct population

Correct Answer: C
Explanation: More young individuals indicate growth.

Q43. J-shaped growth curve represents:
A. Logistic growth
B. Declining growth
C. Exponential growth
D. Zero growth

Correct Answer: C
Explanation: Exponential growth occurs under unlimited resources.

Q44. S-shaped growth curve is typical of:
A. Exponential growth
B. Logistic growth
C. Negative growth
D. Seasonal growth

Correct Answer: B
Explanation: Logistic growth occurs with limited resources.

Q45. Carrying capacity refers to:
A. Maximum birth rate
B. Maximum death rate
C. Maximum sustainable population
D. Maximum growth rate

Correct Answer: C
Explanation: It is the maximum population environment can sustain.

Q46. Mutualism benefits:
A. One species
B. Neither species
C. Both species
D. Predator only

Correct Answer: C
Explanation: Both interacting species benefit.

Q47. Competition occurs when:
A. Resources are abundant
B. Resources are limited
C. Species cooperate
D. One species feeds on another

Correct Answer: B
Explanation: Limited resources lead to competition.

Q48. Predation helps in:
A. Eliminating prey
B. Increasing prey
C. Population regulation
D. Competition

Correct Answer: C
Explanation: Predation controls prey population size.

Q49. Parasitism differs from predation because parasites:
A. Kill host immediately
B. Live on host
C. Do not benefit
D. Are autotrophs

Correct Answer: B
Explanation: Parasites live on or in hosts without immediate killing.

Q50. Interaction where one benefits and other is unaffected is:
A. Mutualism
B. Parasitism
C. Commensalism
D. Amensalism

Correct Answer: C
Explanation: In commensalism, one species benefits while the other is unaffected.

CBSE Exam Tip

These MCQs are ideal for board exam objective sections, concept reinforcement, and competitive exam foundation, strictly aligned with NCERT Biology Chapter 13.

Targeting Exams

• CBSE Class 12 Biology Board Examination

• CBSE School Unit Tests & Pre-Boards

• Term-wise and Annual Assessments

• NEET (UG) – Conceptual Foundation

• Other Class 12 Medical Entrance Preparations

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