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

Course: CBSE Class 12 Biology
Unit V: Ecology and Environment
Topic: Organisms and Populations
Strictly as per NCERT | CBSE Board Exam Oriented | Concept-Clearing Explanations

Section A: Organisms and Environment (Q1–Q15)

Q1. Ecology is the study of

A. plants only
B. animals only
C. interactions between organisms and environment
D. classification of organisms

Correct Answer: C
Explanation: Ecology deals with relationships between organisms and their physical and biological environment.

Q2. Abiotic factors include

A. plants and animals
B. bacteria and fungi
C. temperature, water and light
D. predators and prey

Correct Answer: C
Explanation: Abiotic factors are non-living components like temperature, light, soil and water.

Q3. Which factor mainly affects the distribution of organisms in aquatic environments?

A. Temperature
B. Light
C. Soil
D. Wind

Correct Answer: B
Explanation: Light penetration determines photosynthesis and depth distribution in aquatic ecosystems.

Q4. Stenothermal organisms can tolerate

A. wide temperature range
B. narrow temperature range
C. high salinity
D. low oxygen

Correct Answer: B
Explanation: Stenothermal organisms survive only within a narrow temperature range.

Q5. Eurythermal organisms are those which

A. live in deserts
B. tolerate narrow temperature range
C. tolerate wide temperature range
D. live only in water

Correct Answer: C
Explanation: Eurythermal organisms can survive in a wide range of temperatures.

Q6. Which factor limits plant growth in deserts?

A. Light
B. Water
C. Temperature
D. Wind

Correct Answer: B
Explanation: Scarcity of water is the major limiting factor in deserts.

Q7. Homeostasis refers to

A. population growth
B. maintenance of internal balance
C. migration
D. adaptation

Correct Answer: B
Explanation: Organisms maintain stable internal conditions despite external changes.

Q8. Desert plants show adaptation like

A. broad leaves
B. thin cuticle
C. deep root system
D. large stomata

Correct Answer: C
Explanation: Deep roots help in absorbing underground water.

Q9. Conformers are organisms that

A. maintain constant internal environment
B. change internal conditions with surroundings
C. migrate seasonally
D. hibernate

Correct Answer: B
Explanation: Conformers do not regulate internal environment actively.

Q10. Regulators are organisms that

A. cannot survive environmental changes
B. maintain constant internal conditions
C. live only in water
D. show no adaptation

Correct Answer: B
Explanation: Regulators maintain homeostasis regardless of external conditions.

Q11. Hibernation helps organisms to survive during

A. summer
B. drought
C. winter
D. rainy season

Correct Answer: C
Explanation: Hibernation helps animals survive extreme cold and food scarcity.

Q12. Migration in animals occurs mainly due to

A. reproduction
B. climate change and food availability
C. competition
D. pollution

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

Q13. Adaptation is

A. temporary change
B. structural, physiological or behavioral feature
C. disease resistance
D. migration

Correct Answer: B
Explanation: Adaptations increase survival and reproduction in a given environment.

Q14. Which is an example of physiological adaptation?

A. Camouflage
B. Thick fur
C. Sweating in humans
D. Migration

Correct Answer: C
Explanation: Sweating regulates body temperature.

Q15. Altitude affects organisms mainly due to change in

A. soil
B. oxygen availability
C. water
D. predators

Correct Answer: B
Explanation: Oxygen concentration decreases with altitude.

Section B: Population Attributes and Growth (Q16–Q30)

Q16. A population is defined as

A. group of organisms of different species
B. group of organisms of same species in an area
C. community of organisms
D. ecosystem

Correct Answer: B
Explanation: Population consists of individuals of same species living in a specific area.

Q17. Population density is measured as

A. number of species
B. number of individuals per unit area
C. biomass only
D. age of organisms

Correct Answer: B
Explanation: Population density refers to number of individuals per unit area or volume.

Q18. Which is NOT a population attribute?

A. Birth rate
B. Death rate
C. Age distribution
D. Photosynthesis

Correct Answer: D
Explanation: Photosynthesis is an individual trait, not population attribute.

Q19. Natality refers to

A. death rate
B. birth rate
C. immigration
D. emigration

Correct Answer: B
Explanation: Natality is the rate of addition of new individuals by birth.

Q20. Mortality refers to

A. increase in population
B. decrease in population due to deaths
C. migration
D. reproduction

Correct Answer: B
Explanation: Mortality is the death rate in a population.

Q21. Immigration leads to

A. decrease in population size
B. no change in population
C. increase in population size
D. extinction

Correct Answer: C
Explanation: Immigration adds individuals to a population.

Q22. Emigration results in

A. increase in population
B. decrease in population
C. stability
D. speciation

Correct Answer: B
Explanation: Emigration removes individuals from population.

Q23. Exponential population growth is represented by

A. J-shaped curve
B. S-shaped curve
C. straight line
D. bell curve

Correct Answer: A
Explanation: Unlimited resources lead to exponential growth forming J-curve.

Q24. Logistic population growth shows

A. no limitation
B. unlimited growth
C. carrying capacity
D. extinction

Correct Answer: C
Explanation: Growth slows as population reaches carrying capacity.

Q25. Carrying capacity refers to

A. maximum number environment can support
B. minimum population size
C. reproductive capacity
D. food availability only

Correct Answer: A
Explanation: It is the maximum population size an environment can sustain.

Q26. Population growth rate is affected by

A. natality only
B. mortality only
C. natality, mortality and migration
D. age only

Correct Answer: C
Explanation: All these factors influence population size.

Q27. Age pyramid represents

A. population growth rate
B. age distribution of population
C. death rate
D. migration pattern

Correct Answer: B
Explanation: It shows proportion of individuals in different age groups.

Q28. A declining population shows

A. broad base pyramid
B. bell shaped pyramid
C. narrow base pyramid
D. inverted pyramid

Correct Answer: C
Explanation: Fewer young individuals indicate declining population.

Q29. Which population has stable growth?

A. Expanding
B. Declining
C. Stable
D. Extinct

Correct Answer: C
Explanation: Stable population has nearly equal birth and death rates.

Q30. Population regulation is achieved by

A. unlimited resources
B. environmental resistance
C. migration only
D. reproduction only

Correct Answer: B
Explanation: Environmental resistance controls population growth.

Section C: Population Interactions (Q31–Q50)

Q31. Interaction where both species benefit is called

A. predation
B. parasitism
C. mutualism
D. competition

Correct Answer: C
Explanation: Mutualism benefits both interacting species.

Q32. Lichen is an example of

A. parasitism
B. commensalism
C. mutualism
D. predation

Correct Answer: C
Explanation: Algae and fungi live together benefiting each other.

Q33. In commensalism

A. both species benefit
B. one benefits, other harmed
C. one benefits, other unaffected
D. both harmed

Correct Answer: C
Explanation: One species benefits while the other is neither harmed nor benefited.

Q34. An example of commensalism is

A. lion and deer
B. cattle and cattle egret
C. human and parasite
D. fungi and algae

Correct Answer: B
Explanation: Egret benefits, cattle remains unaffected.

Q35. Predation helps in

A. eliminating prey species
B. maintaining population balance
C. reducing biodiversity
D. causing extinction always

Correct Answer: B
Explanation: Predators regulate prey population.

Q36. In parasitism

A. both benefit
B. parasite benefits, host harmed
C. host benefits
D. none affected

Correct Answer: B
Explanation: Parasite derives nutrition at the expense of host.

Q37. Tapeworm in human intestine shows

A. mutualism
B. commensalism
C. parasitism
D. competition

Correct Answer: C
Explanation: Tapeworm harms host while benefiting itself.

Q38. Competition occurs when

A. resources are unlimited
B. two species require same limited resource
C. predator hunts prey
D. one species benefits

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

Q39. In interspecific competition

A. individuals of same species compete
B. individuals of different species compete
C. organisms migrate
D. species show mutualism

Correct Answer: B
Explanation: Different species compete for same resource.

Q40. Amensalism refers to

A. both species harmed
B. one harmed, other unaffected
C. both benefited
D. one benefited, other harmed

Correct Answer: B
Explanation: One species is inhibited while other remains unaffected.

Q41. Antibiotic secretion by fungi killing bacteria is

A. mutualism
B. commensalism
C. amensalism
D. parasitism

Correct Answer: C
Explanation: Bacteria are harmed, fungi unaffected.

Q42. Co-evolution refers to

A. independent evolution
B. simultaneous evolution of interacting species
C. extinction
D. mutation

Correct Answer: B
Explanation: Species evolve in response to each other.

Q43. Predator-prey interaction is best described by

A. Lotka–Volterra model
B. Hardy–Weinberg principle
C. Mendel’s laws
D. Logistic equation

Correct Answer: A
Explanation: It explains oscillations in predator and prey populations.

Q44. Mimicry helps prey by

A. increasing size
B. attracting predators
C. avoiding predators
D. increasing reproduction

Correct Answer: C
Explanation: Mimicry reduces chances of predation.

Q45. Camouflage is a

A. physiological adaptation
B. behavioral adaptation
C. structural adaptation
D. population attribute

Correct Answer: C
Explanation: Structural similarity helps organisms blend with surroundings.

Q46. Herbivory refers to

A. plant eating animals
B. animal eating animals
C. parasite feeding
D. decomposers feeding

Correct Answer: A
Explanation: Herbivores feed on plants.

Q47. Secondary productivity refers to

A. plant biomass production
B. animal biomass production
C. decomposition
D. nutrient cycling

Correct Answer: B
Explanation: It is rate of biomass production by consumers.

Q48. Population interactions help in

A. ecosystem stability
B. extinction
C. pollution
D. isolation

Correct Answer: A
Explanation: Interactions maintain balance in ecosystems.

Q49. Keystone species are important because they

A. are most abundant
B. have disproportionate impact on ecosystem
C. are always predators
D. live longest

Correct Answer: B
Explanation: Their removal drastically affects ecosystem structure.

Q50. Organisms and populations together form

A. biome
B. ecosystem
C. biosphere
D. community

Correct Answer: B
Explanation: Ecosystem includes organisms, populations and environment.

✅ End of MCQs – Organisms and Populations (Class 12 Biology, NCERT)