CBSE Class 12 Biology MCQ – Organisms and Populations

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Organisms and Populations MCQ: The chapter “Organisms and Populations” is a crucial part of Class 12 Biology, focusing on the interactions between living organisms and their environment. It delves into topics like adaptations, population dynamics, ecological relationships, and the influence of abiotic factors on living beings. This chapter bridges ecology and biology, offering insights into how species coexist, compete, and thrive in diverse habitats. Practicing MCQs on these topics strengthens conceptual clarity and prepares students for exams effectively.

Organisms and Populations MCQ

The chapter “Organisms and Populations” in Class 12 Biology explores the interactions between organisms and their environment. It covers key topics like the influence of abiotic factors, adaptations in organisms, population growth models, population interactions (mutualism, competition, predation, and parasitism), and the dynamics of ecosystems. This chapter is critical for understanding ecological principles and species survival strategies. Solving Organisms and Populations MCQ on these topics helps in mastering concepts, improving problem-solving skills, and aligning with the CBSE syllabus requirements, ensuring better preparation for board exams and competitive tests like NEET.

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Organisms and Populations MCQ with Answers

Q1. Which of the following is NOT a density-dependent factor in population regulation?
a) Competition
b) Predation
c) Flood
d) Parasitism
Answer: c) Flood

Q2. The intrinsic rate of increase (r) is highest in which of the following species?
a) Elephants
b) Bacteria
c) Humans
d) Tigers
Answer: b) Bacteria

Q3. Which interaction benefits both participating species?
a) Predation
b) Mutualism
c) Commensalism
d) Parasitism
Answer: b) Mutualism

Q4. What does the carrying capacity (K) of an environment signify?
a) Maximum population size the environment can sustain
b) Total biomass of the ecosystem
c) Unlimited resource availability
d) Rate of population growth
Answer: a) Maximum population size the environment can sustain

Q5. In a logistic growth model, what happens when the population size (N) approaches carrying capacity (K)?
a) Growth rate increases exponentially
b) Growth rate becomes zero
c) Growth rate remains constant
d) Growth rate becomes negative
Answer: b) Growth rate becomes zero

Q6. What is the primary mode of interaction in a predator-prey relationship?
a) Competition
b) Exploitation
c) Neutralism
d) Mutualism
Answer: b) Exploitation

Q7. Which of the following is an example of commensalism?
a) Orchid growing on a mango tree
b) Cattle and cattle egret
c) Clownfish and sea anemone
d) Flea on a dog
Answer: b) Cattle and cattle egret

Q8. Allen’s rule applies to which type of organisms?
a) Marine species
b) Desert species
c) Endothermic animals in cold regions
d) Amphibians in tropical regions
Answer: c) Endothermic animals in cold regions

Q9. Which of the following is a K-selected species?
a) Fruit fly
b) Bamboo
c) Blue whale
d) Cockroach
Answer: c) Blue whale

Q10. In plants, the term ‘allelopathy’ refers to:
a) Symbiotic relationships
b) Chemical inhibition of one species by another
c) Cross-pollination mechanisms
d) Population growth strategies
Answer: b) Chemical inhibition of one species by another

Q11. What does a J-shaped curve in population growth indicate?
a) Logistic growth
b) Exponential growth
c) Declining population
d) Stable population
Answer: b) Exponential growth

Q12. Which interaction negatively affects both species?
a) Competition
b) Predation
c) Parasitism
d) Commensalism
Answer: a) Competition

Q13. In which environment would you most likely find animals with thick fur and fat layers?
a) Desert
b) Grassland
c) Polar region
d) Tropical rainforest
Answer: c) Polar region

Q14. Population density is measured as:
a) Total individuals in a population
b) Individuals per unit area
c) Growth rate per year
d) Biomass per unit area
Answer: b) Individuals per unit area

Q15. Which factor leads to random distribution of a population?
a) Resource abundance
b) Predation pressure
c) Social hierarchy
d) Uniform resource availability
Answer: d) Uniform resource availability

Q16. Which is an example of secondary succession?
a) Colonization of lava fields
b) Reforestation of a cleared forest
c) Formation of coral reefs
d) Glacier melting and soil development
Answer: b) Reforestation of a cleared forest

Q17. Age pyramids are used to represent:
a) Energy flow in ecosystems
b) Population distribution by age
c) Biogeochemical cycles
d) Growth curves in animals
Answer: b) Population distribution by age

Q18. What type of interaction is exhibited by lichens?
a) Mutualism
b) Parasitism
c) Commensalism
d) Amensalism
Answer: a) Mutualism

Q19. The term ‘ecotype’ refers to:
a) Local adaptation within a species
b) Evolutionary divergence of populations
c) Global species variation
d) Inter-species hybridization
Answer: a) Local adaptation within a species

Q20. Primary productivity in an ecosystem is affected by:
a) Population size
b) Temperature and light
c) Competition levels
d) Trophic interactions
Answer: b) Temperature and light

Q21. The relationship between cattle and gut bacteria is an example of:
a) Parasitism
b) Mutualism
c) Commensalism
d) Predation
Answer: b) Mutualism

Q22. Which species is most likely to exhibit clumped distribution?
a) Birds in migration
b) Solitary carnivores
c) Fish in a school
d) Grass in a meadow
Answer: c) Fish in a school

Q23. Which gas is most associated with global warming affecting organisms?
a) Nitrogen
b) Oxygen
c) Carbon dioxide
d) Methane
Answer: c) Carbon dioxide

Q24. The concept of ‘r-strategy’ in reproduction includes:
a) Large body size
b) High offspring number
c) Long lifespan
d) High parental care
Answer: b) High offspring number

Q25. Which factor triggers seed dormancy in desert plants?
a) High water availability
b) Low temperatures
c) High salt concentration
d) Scarce rainfall
Answer: d) Scarce rainfall

Q26. Which is NOT an example of an abiotic factor?
a) Temperature
b) Light
c) Soil
d) Pollination
Answer: d) Pollination

Q27. What is the term for species that serve as indicators of environmental health?
a) Keystone species
b) Indicator species
c) Invasive species
d) Dominant species
Answer: b) Indicator species

Q28. What does Gause’s Competitive Exclusion Principle state?
a) Two species can coexist without competition.
b) No two species can occupy the same niche indefinitely.
c) Symbiotic species never compete.
d) Populations grow at exponential rates.
Answer: b) No two species can occupy the same niche indefinitely.

Q29. Which population growth model best applies to humans?
a) J-shaped curve
b) S-shaped curve
c) Linear growth
d) Exponential growth
Answer: b) S-shaped curve

Q30. Which process contributes to genetic variation in a population?
a) Natural selection
b) Mutations
c) Competition
d) Parasitism
Answer: b) Mutations