Class 12 Biology MCQ – Organisms and Populations

1. Which of the following is NOT an abiotic factor in an ecosystem?

a) Temperature
b) Soil
c) Bacteria
d) Light

Answer:

c) Bacteria

Explanation:

Bacteria are living organisms and therefore are considered biotic factors in an ecosystem.

2. The phenomenon where some organisms suspend their metabolic activities during unfavorable conditions is called:

a) Hibernation
b) Estivation
c) Diapause
d) Dormancy

Answer:

c) Diapause

Explanation:

Diapause is a period of suspended development and activity in insects and some other animals to survive unfavorable conditions.

3. Which is a behavioral adaptation of desert plants to reduce water loss?

a) Thick cuticle
b) Deep roots
c) Opening stomata at night
d) Large leaves

Answer:

c) Opening stomata at night

Explanation:

Opening stomata at night (CAM plants) is a strategy to minimize water loss through transpiration during the heat of the day.

4. The population interaction in which both species are harmed is called:

a) Mutualism
b) Commensalism
c) Amensalism
d) Competition

Answer:

d) Competition

Explanation:

In competition, both species are harmed as they vie for the same limited resources.

5. The maximum number of individuals a habitat can support indefinitely is termed:

a) Carrying capacity
b) Ecological niche
c) Biotic potential
d) Population density

Answer:

a) Carrying capacity

Explanation:

Carrying capacity is the maximum population size that can be supported indefinitely without degrading the habitat.

6. Which of the following is a density-independent factor affecting population size?

a) Predation
b) Food availability
c) Temperature extremes
d) Disease

Answer:

c) Temperature extremes

Explanation:

Density-independent factors, like temperature extremes, affect populations regardless of their density.

7. Organisms that have a short lifespan and produce a large number of offspring are called:

a) r-strategists
b) K-strategists
c) Commensalists
d) Mutualists

Answer:

a) r-strategists

Explanation:

r-strategists are adapted for rapid growth and reproduction in environments where resources are temporarily abundant.

8. Which type of population distribution is most common in nature?

a) Random
b) Uniform
c) Clumped
d) Linear

Answer:

c) Clumped

Explanation:

Clumped distribution, where individuals group together in patches, is the most common distribution pattern in nature.

9. The term used to describe the role an organism plays in its ecosystem is:

a) Habitat
b) Niche
c) Biome
d) Trophic level

Answer:

b) Niche

Explanation:

The niche of an organism describes its role in the ecosystem, including its interactions with other organisms and its environment.

10. The adaptation of cacti having spines instead of leaves helps to:

a) Attract pollinators
b) Reduce water loss
c) Absorb more sunlight
d) Defend against herbivores

Answer:

b) Reduce water loss

Explanation:

The transformation of leaves into spines reduces the surface area, thereby minimizing water loss through transpiration.

11. Which of the following is a biotic factor in an ecosystem?

a) Wind
b) Humidity
c) Predation
d) Altitude

Answer:

c) Predation

Explanation:

Predation involves interactions between living organisms, making it a biotic factor.

12. Populations of which of the following would be most affected by a density-dependent factor?

a) Sparse populations
b) Dense populations
c) Randomly distributed populations
d) Uniformly distributed populations

Answer:

b) Dense populations

Explanation:

Density-dependent factors, like competition and disease, have a greater impact as population density increases.

13. A population showing a J-shaped growth curve is experiencing:

a) Exponential growth
b) Logistic growth
c) Oscillating growth
d) Zero growth

Answer:

a) Exponential growth

Explanation:

A J-shaped growth curve represents a population growing without any limiting factors, resulting in exponential growth.

14. Which of the following is NOT a characteristic of K-strategists?

a) Long lifespan
b) Many offspring
c) Late maturity
d) Stable environments

Answer:

b) Many offspring

Explanation:

K-strategists produce fewer, but more well-cared-for offspring, adapting to environments where the population size is near the carrying capacity.

15. In which type of interaction is one species benefited while the other is neither benefited nor harmed?

a) Mutualism
b) Parasitism
c) Commensalism
d) Amensalism

Answer:

c) Commensalism

Explanation:

In commensalism, one organism benefits while the other is unaffected.

16. The broadest level of ecological study is the:

a) Community
b) Ecosystem
c) Population
d) Biosphere

Answer:

d) Biosphere

Explanation:

The biosphere encompasses all living organisms and their environments on Earth.

17. The range of tolerance in an organism denotes:

a) The range of habitats it can occupy
b) The limits within which it can survive and reproduce
c) Its reproductive potential
d) Its feeding habits

Answer:

b) The limits within which it can survive and reproduce

Explanation:

The range of tolerance defines the conditions under which an organism can thrive, beyond which it experiences stress.

18. Which factor is most responsible for the vertical stratification of a forest?

a) Soil type
b) Temperature
c) Light availability
d) Wind pattern

Answer:

c) Light availability

Explanation:

Light availability varies with height, leading to layers (strata) of plant growth in forests.

19. The phenomenon where one organism lives inside another and benefits at the expense of the host is:

a) Commensalism
b) Mutualism
c) Parasitism
d) Amensalism

Answer:

c) Parasitism

Explanation:

In parasitism, the parasite derives benefits at the expense of the host, often causing harm.

20. The sum total of all the populations living in an area is termed:

a) Ecosystem
b) Community
c) Habitat
d) Biosphere

Answer:

b) Community

Explanation:

A community encompasses all the different populations that live and interact in an area.

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