ROUTERA


Chapter 13 Organisms and Populations

Class 12th Biology Chapter MCQs


1. Which of the following is the primary factor determining the distribution of organisms?

  • A) Temperature
  • B) Soil type
  • C) Water
  • D) All of the above

Answer: D
Explanation: The distribution of organisms is influenced by multiple factors like temperature, soil type, and water, which all shape the environment of a species.


2. Which of the following is an example of a biotic factor influencing the population of an organism?

  • A) Temperature
  • B) Light
  • C) Predators
  • D) Soil type

Answer: C
Explanation: Predators are biotic factors that influence the population of organisms by hunting and consuming them.


3. The carrying capacity of a population refers to:

  • A) The maximum number of individuals that a habitat can support over time.
  • B) The growth rate of a population
  • C) The average size of individuals in a population
  • D) The ability of an individual to adapt to the environment

Answer: A
Explanation: Carrying capacity refers to the maximum population size that an environment can support sustainably.


4. In which type of population growth does the growth rate decrease as the population size approaches the carrying capacity?

  • A) Exponential growth
  • B) Logistic growth
  • C) Geometric growth
  • D) Linear growth

Answer: B
Explanation: Logistic growth occurs when the growth rate decreases as the population reaches its carrying capacity, forming an S-shaped curve.


5. Which of the following is NOT an adaptation of organisms in desert environments?

  • A) Small leaves to reduce transpiration
  • B) Ability to store water in tissues
  • C) Thick fur for insulation
  • D) High metabolic rate

Answer: D
Explanation: A high metabolic rate is not an adaptation in deserts. Instead, organisms conserve energy and water by adopting lower metabolic rates.


6. Which of the following is an example of a density-independent factor?

  • A) Predation
  • B) Disease
  • C) Earthquake
  • D) Competition

Answer: C
Explanation: Earthquakes are density-independent factors, meaning their effect on population size is not influenced by the population's density.


7. In the population growth equation, which term represents the rate of population increase per individual?

  • A) r
  • B) K
  • C) N
  • D) S

Answer: A
Explanation: The term r represents the intrinsic rate of population growth, indicating how quickly a population can increase under ideal conditions.


8. Which of the following is an example of mutualism?

  • A) A lion hunting a zebra
  • B) A bee pollinating a flower
  • C) A tick feeding on a dog
  • D) A bird eating ticks from a zebra's skin

Answer: B
Explanation: In mutualism, both organisms benefit. In this case, the bee pollinates the flower and gets nectar, while the plant gets pollinated.


9. Which of the following is an example of a r-strategist?

  • A) Elephant
  • B) Whale
  • C) Rabbit
  • D) Oak tree

Answer: C
Explanation: r-strategists like rabbits have high reproductive rates, producing many offspring with little parental care.


10. What is the primary characteristic of K-strategists?

  • A) Small size and early reproduction
  • B) Large size and long lifespan
  • C) Large number of offspring
  • D) Quick population growth

Answer: B
Explanation: K-strategists tend to be larger in size, reproduce later in life, and produce fewer offspring with extensive parental care.


11. Which of the following refers to the non-living factors affecting organisms in an ecosystem?

  • A) Biotic factors
  • B) Abiotic factors
  • C) Population dynamics
  • D) Community interactions

Answer: B
Explanation: Abiotic factors include non-living components of the environment, such as temperature, light, and water.


12. Which of the following is an example of a climax community?

  • A) A newly formed volcanic island
  • B) A mature temperate forest
  • C) A grassland after a fire
  • D) A pond that dries up during the summer

Answer: B
Explanation: A mature temperate forest is considered a climax community, which is the stable and final stage of ecological succession.


13. Which term refers to the maximum reproductive capacity of an organism?

  • A) Biotic potential
  • B) Carrying capacity
  • C) Ecological niche
  • D) Limiting factor

Answer: A
Explanation: Biotic potential refers to the maximum reproductive capacity of an organism under optimal environmental conditions.


14. Which of the following is an example of a type III survivorship curve?

  • A) Humans
  • B) Elephants
  • C) Oak trees
  • D) Fish

Answer: D
Explanation: A type III survivorship curve shows high mortality at early ages, typical of species like fish that produce many offspring with little parental care.


15. Which of the following is NOT an example of interspecific competition?

  • A) Two species of birds fighting over the same nest
  • B) A lion and a hyena fighting for the same food
  • C) A rabbit and a deer eating the same type of grass
  • D) A lion hunting a gazelle

Answer: D
Explanation: Interspecific competition refers to competition between different species, not predation. A lion hunting a gazelle is an example of predation, not competition.


16. Which of the following is an example of the Lotka-Volterra model of predator-prey interactions?

  • A) Logistic growth model
  • B) The oscillations in the population of wolves and deer
  • C) The growth of a bacterial culture
  • D) The growth of a plant in a garden

Answer: B
Explanation: The Lotka-Volterra model explains the oscillating populations of predators (wolves) and prey (deer) due to their interactions.


17. Which of the following factors does NOT affect the size of a population?

  • A) Immigration
  • B) Emigration
  • C) Mortality
  • D) Density-independent factors

Answer: D
Explanation: Density-independent factors such as natural disasters do not depend on population size and affect the population regardless of its size.


18. Which of the following is a feature of a population exhibiting exponential growth?

  • A) Growth slows as resources become limiting
  • B) The population reaches a carrying capacity
  • C) The population grows at a constant rate
  • D) The population size increases in a sigmoidal curve

Answer: C
Explanation: In exponential growth, the population grows at a constant rate, forming a J-shaped curve, without resource limitations.


19. Which of the following is a characteristic of organisms in a savanna ecosystem?

  • A) Adapted to cold temperatures
  • B) Limited rainfall and long dry periods
  • C) Dense vegetation
  • D) Presence of tall coniferous trees

Answer: B
Explanation: Savanna ecosystems have limited rainfall and long dry seasons, with grasses and sparse trees.


20. In which type of population interaction do both species benefit?

  • A) Mutualism
  • B) Parasitism
  • C) Amensalism
  • D) Commensalism

Answer: A
Explanation: Mutualism is a type of interaction where both species benefit, like bees and flowers.


21. Which of the following is true regarding an ecological niche?

  • A) It is the place where an organism lives
  • B) It is the role an organism plays in the ecosystem
  • C) It only refers to the species' habitat
  • D) It is always a static and unchanging factor

Answer: B
Explanation: An ecological niche refers to the role an organism plays in its ecosystem, including its interactions with other species and the environment.


22. What happens when two species occupy the same ecological niche?

  • A) They will always coexist peacefully
  • B) One species will outcompete the other
  • C) Both species will thrive equally
  • D) Both species will evolve into a single species

Answer: B
Explanation: When two species occupy the same ecological niche, one species will likely outcompete the other due to resource limitations (competitive exclusion principle).


23. Which of the following factors are abiotic?

  • A) Predators and competitors
  • B) Temperature and light
  • C) Disease and parasites
  • D) Food and mates

Answer: B
Explanation: Abiotic factors are non-living components of the environment like temperature and light.


24. Which type of ecological succession occurs after a forest fire?

  • A) Primary succession
  • B) Secondary succession
  • C) Tertiary succession
  • D) Pioneer succession

Answer: B
Explanation: Secondary succession occurs after a disturbance such as a forest fire, where the soil is still intact.


25. Which of the following is a characteristic of K-strategists?

  • A) Produce many offspring with little parental care
  • B) Reproduce early in life
  • C) Have a long lifespan and slow reproductive rate
  • D) Adapt to unpredictable environments

Answer: C
Explanation: K-strategists have long lifespans, produce fewer offspring, and invest more in their survival and growth.


26. Which of the following is an example of a population?

  • A) All the different species in a forest
  • B) A single tree in a forest
  • C) All the squirrels in a forest
  • D) All the biotic and abiotic factors in a pond

Answer: C
Explanation: A population refers to a group of individuals of the same species living in a specific geographic area and interacting with each other.


27. Which of the following would result in a stable population size?

  • A) Immigration rate greater than the birth rate
  • B) Birth rate equal to death rate
  • C) Emigration rate greater than the birth rate
  • D) High death rate

Answer: B
Explanation: A stable population size occurs when the birth rate is equal to the death rate, meaning the population neither increases nor decreases.


28. Which of the following describes a density-dependent factor?

  • A) Natural disaster
  • B) Temperature extremes
  • C) Food availability
  • D) Rainfall

Answer: C
Explanation: Food availability is a density-dependent factor, as its effect on the population size becomes more significant when the population density is high.


29. Which of the following is a characteristic feature of a pioneer species in an ecosystem?

  • A) Large body size
  • B) Ability to survive in harsh conditions
  • C) Long lifespan
  • D) Need for complex food chains

Answer: B
Explanation: Pioneer species are the first organisms to colonize a barren environment. They are often hardy and can survive in harsh conditions.


30. The process of natural selection involves which of the following?

  • A) Survival of the fittest
  • B) Random changes in genetic material
  • C) Mating between individuals of different species
  • D) Reproduction of organisms with unfavorable traits

Answer: A
Explanation: Natural selection is the process by which organisms with traits that are favorable for survival and reproduction are more likely to pass on their genes to the next generation.


31. Which of the following strategies is most commonly associated with r-strategists?

  • A) Few offspring, high parental care
  • B) Many offspring, little parental care
  • C) Long lifespan
  • D) Stable populations

Answer: B
Explanation: r-strategists produce many offspring but provide little or no parental care. They typically live in unstable environments where rapid reproduction is advantageous.


32. Which type of population growth is exhibited by a population in an environment with unlimited resources?

  • A) Exponential growth
  • B) Logistic growth
  • C) Cyclic growth
  • D) Irregular growth

Answer: A
Explanation: Exponential growth occurs when a population grows rapidly without any environmental constraints or limitations, typically seen when resources are abundant.


33. Which of the following is an example of resource partitioning?

  • A) Lions and hyenas competing for the same prey
  • B) Birds feeding on different parts of the same tree
  • C) Cheetahs and leopards hunting in the same area
  • D) Trees in a forest competing for sunlight

Answer: B
Explanation: Resource partitioning occurs when different species use the same resource in different ways, such as birds feeding on different parts of the same tree to reduce competition.


34. Which of the following does NOT affect the population density of an organism?

  • A) Immigration
  • B) Emigration
  • C) Food availability
  • D) Age of individual organisms

Answer: D
Explanation: Age of individual organisms does not directly affect population density, but factors like immigration, emigration, and food availability do.


35. Which of the following is the primary cause of death in organisms in a natural population?

  • A) Lack of food
  • B) Overcrowding
  • C) Predation
  • D) Genetic mutation

Answer: C
Explanation: Predation is one of the primary causes of mortality in natural populations, where predators hunt and consume other organisms.


36. Which of the following organisms is most likely to be an r-strategist?

  • A) Whale
  • B) Tortoise
  • C) Frog
  • D) Elephant

Answer: C
Explanation: Frogs are typical examples of r-strategists as they lay many eggs with little to no parental care.


37. Which of the following is a feature of an invasive species?

  • A) Limited geographic distribution
  • B) Slow reproduction rate
  • C) Ability to outcompete native species
  • D) Low genetic diversity

Answer: C
Explanation: Invasive species are typically able to outcompete native species for resources, often leading to the decline or extinction of native species.


38. Which of the following is an example of an animal exhibiting Type I survivorship curve?

  • A) Insects
  • B) Oak trees
  • C) Humans
  • D) Sea turtles

Answer: C
Explanation: Humans exhibit a Type I survivorship curve, where most individuals survive to old age, with high survival rates during early and middle life.


39. Which of the following best describes a K-strategist’s reproductive strategy?

  • A) High number of offspring with little parental care
  • B) High number of offspring with significant parental care
  • C) Few offspring with no parental care
  • D) Few offspring with significant parental care

Answer: D
Explanation: K-strategists tend to have few offspring but invest significantly in their care to ensure their survival.


40. Which of the following is NOT a type of symbiotic relationship?

  • A) Mutualism
  • B) Commensalism
  • C) Parasitism
  • D) Herbivory

Answer: D
Explanation: Herbivory is not a type of symbiosis but an interaction where an herbivore feeds on plants, while mutualism, commensalism, and parasitism are all types of symbiotic relationships.


41. Which of the following factors would most likely cause a population to exhibit logistic growth?

  • A) Unlimited resources and no competition
  • B) Limited resources and competition
  • C) High mortality rates
  • D) High immigration rate

Answer: B
Explanation: Logistic growth occurs when resources are limited and there is competition, leading to a population growing until it reaches the carrying capacity.


42. Which of the following strategies do organisms in a high-stress environment typically adopt?

  • A) High reproductive rate
  • B) Large body size
  • C) Slow growth
  • D) Limited dispersal

Answer: C
Explanation: Organisms in high-stress environments often exhibit slow growth as they conserve energy to cope with environmental challenges.


43. Which of the following is an example of a density-independent factor?

  • A) Predation
  • B) Disease
  • C) Forest fire
  • D) Competition

Answer: C
Explanation: Forest fires are density-independent factors because their impact on population size is independent of the population density.


44. Which of the following is the primary determinant of the population growth rate?

  • A) Birth rate
  • B) Immigration rate
  • C) Death rate
  • D) Carrying capacity

Answer: A
Explanation: Birth rate primarily determines the population growth rate, as the number of births directly influences the size of the population.


45. Which type of competition occurs between members of different species?

  • A) Intraspecific competition
  • B) Interspecific competition
  • C) Resource partitioning
  • D) Symbiosis

Answer: B
Explanation: Interspecific competition occurs when individuals from different species compete for the same resources.


46. What is the main cause of the population growth rate to slow down in a logistic growth model?

  • A) Decreased competition
  • B) Increased immigration
  • C) Limited resources
  • D) Reduced death rates

Answer: C
Explanation: In the logistic growth model, the population growth slows down as resources become limited, leading to a balance between birth rates and death rates.


47. What does the term "carrying capacity" refer to?

  • A) The maximum number of individuals that can survive in an ecosystem
  • B) The maximum population growth rate
  • C) The number of individuals that a population can double every year
  • D) The area of the habitat available for a population

Answer: A
Explanation: Carrying capacity refers to the maximum number of individuals an environment can support sustainably due to limited resources.


48. Which of the following is an example of a mutualistic relationship?

  • A) Lichens (algae and fungi)
  • B) Predator-prey interactions
  • C) Parasitic worm and host
  • D) Competition for resources

Answer: A
Explanation: Lichens, consisting of algae and fungi, form a mutualistic relationship, where both organisms benefit from the partnership.


49. Which of the following is most likely to result in population stabilization?

  • A) Increased food supply
  • B) Decreased death rate
  • C) Equal birth and death rates
  • D) Increased immigration rate

Answer: C
Explanation: Population stabilization occurs when birth rates and death rates are equal, leading to a steady population size.


50. Which of the following is a feature of the exponential growth phase of a population?

  • A) High birth rate
  • B) Limited resources
  • C) High death rate
  • D) Carrying capacity reached

Answer: A
Explanation: During the exponential growth phase, the population grows rapidly with high birth rates and unlimited resources.