Chapter 13: Organisms and Populations – MCQs
🟢 Organisms and Populations (Q1–Q25)
Q1. Ecology is the study of
a) Cells
b) Tissues
c) Organisms in relation to their environment
d) Evolution
Answer: c) Organisms in relation to their environment
Explanation: Ecology deals with interactions between organisms and their physical/biological environment.
Q2. The functional unit of ecology is
a) Species
b) Population
c) Community
d) Ecosystem
Answer: d) Ecosystem
Explanation: Ecosystem includes both biotic and abiotic interactions.
Q3. The study of population dynamics is called
a) Cytology
b) Demography
c) Taxonomy
d) Morphology
Answer: b) Demography
Explanation: Demography deals with birth rate, death rate, age structure, and population growth.
Q4. Which of the following is an abiotic factor?
a) Predation
b) Temperature
c) Competition
d) Parasitism
Answer: b) Temperature
Explanation: Abiotic = non-living components such as temperature, water, light, soil.
Q5. Homeostasis in living organisms refers to
a) Maintaining constant internal environment
b) Adapting genetically
c) Changing behavior
d) Hibernating
Answer: a) Maintaining constant internal environment
Explanation: Homeostasis allows survival despite external environmental changes.
Q6. The ability of an organism to survive and reproduce in a particular environment is called
a) Fitness
b) Adaptation
c) Acclimatization
d) Evolution
Answer: a) Fitness
Explanation: Darwin defined fitness as the reproductive success of an organism.
Q7. Kangaroo rats conserve water by
a) Drinking large amounts
b) Producing concentrated urine and dry feces
c) Living in humid burrows
d) Eating moist plants
Answer: b) Producing concentrated urine and dry feces
Explanation: They never drink water; obtain water metabolically from seeds.
Q8. Hibernation is an adaptation for
a) Heat tolerance
b) Cold conditions
c) Water conservation
d) Predator avoidance
Answer: b) Cold conditions
Explanation: Many animals (e.g., bears, bats) reduce metabolic activity during winters.
Q9. The population size at a given time is represented by
a) N
b) K
c) r
d) dN/dt
Answer: a) N
Explanation: N denotes number of individuals in a population at a specific time.
Q10. Carrying capacity (K) refers to
a) Maximum number a habitat can support
b) Total number of species present
c) Population growth rate
d) Half of population size
Answer: a) Maximum number a habitat can support
Explanation: Limited by resources, space, and environmental resistance.
Q11. Exponential population growth occurs when
a) Resources are unlimited
b) Predators are abundant
c) Resources are limiting
d) Death rate > Birth rate
Answer: a) Resources are unlimited
Explanation: In ideal conditions, growth follows J-shaped curve.
Q12. Logistic growth curve is represented by
a) J-shaped curve
b) S-shaped curve
c) Straight line
d) Bell-shaped curve
Answer: b) S-shaped curve
Explanation: Logistic growth considers environmental resistance and carrying capacity.
Q13. The intrinsic rate of natural increase is denoted by
a) r
b) K
c) N
d) λ
Answer: a) r
Explanation: r measures per capita birth rate minus death rate under ideal conditions.
Q14. Which of the following is an r-selected species trait?
a) Long lifespan
b) Few offspring
c) High parental care
d) High reproductive rate
Answer: d) High reproductive rate
Explanation: r-strategists produce many offspring, mature quickly, low survival rate.
Q15. A K-selected species is characterized by
a) High reproductive rate
b) Small size, short life span
c) Few offspring with high survival
d) Opportunistic colonization
Answer: c) Few offspring with high survival
Explanation: K-strategists show parental care and stable populations near carrying capacity.
Q16. The sum total of all adaptations by which an organism survives in its habitat is
a) Habitat
b) Niche
c) Territory
d) Biome
Answer: b) Niche
Explanation: Niche = functional role of species, including its adaptations and interactions.
Q17. The relationship between cattle egret and grazing cattle is
a) Mutualism
b) Commensalism
c) Parasitism
d) Predation
Answer: b) Commensalism
Explanation: Egrets feed on insects stirred up by cattle, cattle unaffected.
Q18. The lichen association is an example of
a) Competition
b) Mutualism
c) Amensalism
d) Commensalism
Answer: b) Mutualism
Explanation: Fungus and alga/cyanobacterium both benefit.
Q19. In predation, one species
a) Benefits, other unaffected
b) Both benefit
c) One benefits, other harmed
d) Both harmed
Answer: c) One benefits, other harmed
Explanation: Predator benefits by eating prey, prey gets killed.
Q20. The logistic growth equation is
a) dN/dt = rN
b) dN/dt = rN[(K-N)/K]
c) dN/dt = K-N
d) dN/dt = r/K
Answer: b) dN/dt = rN[(K-N)/K]
Explanation: Incorporates carrying capacity K, resulting in S-shaped growth.
Q21. Intraspecific competition occurs between
a) Lion and deer
b) Cow and goat
c) Two tigers
d) Sparrow and crow
Answer: c) Two tigers
Explanation: Competition between individuals of same species for similar resources.
Q22. The interaction where one species is harmed and other unaffected is
a) Commensalism
b) Amensalism
c) Mutualism
d) Predation
Answer: b) Amensalism
Explanation: Example: Penicillium secretes penicillin that inhibits bacteria.
Q23. Which one is an ectoparasite?
a) Malarial parasite
b) Head louse
c) Tapeworm
d) Ascaris
Answer: b) Head louse
Explanation: Ectoparasites live on body surface of host.
Q24. Brood parasitism in cuckoo is
a) Mutualism
b) Commensalism
c) Parasitism
d) Amensalism
Answer: c) Parasitism
Explanation: Cuckoo lays eggs in crow’s nest; crow rears them.
Q25. Which curve best represents survivorship in humans?
a) Type I
b) Type II
c) Type III
d) Type IV
Answer: a) Type I
Explanation: Type I survivorship curve shows high survival in early/mid life, mortality in old age.
🟢 Part 2: Ecology and Environment – Organisms and Populations (Q26–Q50)
Q26. Which is a density-independent factor in population regulation?
a) Food availability
b) Predation
c) Flood
d) Competition
Answer: c) Flood
Explanation: Natural disasters regulate populations irrespective of density.
Q27. Carrying capacity is determined by
a) Natality and mortality only
b) Resources and environmental resistance
c) Migration alone
d) Birth rate alone
Answer: b) Resources and environmental resistance
Explanation: Limited food, water, and space decide maximum sustainable population size.
Q28. Which interaction is “+ +”?
a) Mutualism
b) Amensalism
c) Commensalism
d) Predation
Answer: a) Mutualism
Explanation: Both species benefit in mutualism (e.g., mycorrhiza, lichen).
Q29. Which interaction is “+ 0”?
a) Amensalism
b) Commensalism
c) Parasitism
d) Competition
Answer: b) Commensalism
Explanation: One benefits, the other is unaffected (e.g., cattle egret).
Q30. Which interaction is “– –”?
a) Mutualism
b) Amensalism
c) Competition
d) Predation
Answer: c) Competition
Explanation: Both species are negatively affected when competing for resources.
Q31. Allelopathy is a form of
a) Predation
b) Mutualism
c) Amensalism
d) Commensalism
Answer: c) Amensalism
Explanation: One species releases chemicals that harm another (e.g., penicillin).
Q32. The ecological niche is best described as
a) Physical space occupied by organism
b) Functional role of species in ecosystem
c) Geographic area of population
d) Habitat of community
Answer: b) Functional role of species in ecosystem
Explanation: Niche = organism’s role, resource use, and interactions.
Q33. Logistic growth of a population occurs when
a) Resources are unlimited
b) Resources are limited
c) Predators are absent
d) Migration is maximum
Answer: b) Resources are limited
Explanation: Limited resources → S-shaped growth with carrying capacity.
Q34. Which of the following is NOT an adaptation to extreme environments?
a) Thick cuticle in desert plants
b) CAM photosynthesis in cacti
c) Hibernation in polar bear
d) High seed dispersal
Answer: d) High seed dispersal
Explanation: Dispersal is not an adaptation to extreme environments.
Q35. Organisms that maintain constant body temperature are called
a) Poikilotherms
b) Homeotherms
c) Osmoconformers
d) Thermoconformers
Answer: b) Homeotherms
Explanation: Birds and mammals regulate body temperature via metabolism and insulation.
Q36. Which of the following is NOT a density-dependent factor?
a) Predation
b) Food competition
c) Disease
d) Earthquake
Answer: d) Earthquake
Explanation: Natural disasters affect population irrespective of density.
Q37. A J-shaped growth curve is shown by
a) Logistic growth
b) Exponential growth
c) Stable population
d) Declining population
Answer: b) Exponential growth
Explanation: Occurs when resources are unlimited.
Q38. Natality means
a) Number of births per 1000 population per year
b) Number of deaths per year
c) Immigration rate
d) Emigration rate
Answer: a) Number of births per 1000 population per year
Explanation: Natality = birth rate, adding individuals to a population.
Q39. Immigration leads to
a) Decrease in population size
b) Increase in population size
c) Stabilization of growth
d) Decline in carrying capacity
Answer: b) Increase in population size
Explanation: Immigration = arrival of new individuals.
Q40. Predation is important because it
a) Increases prey population
b) Maintains population balance
c) Destroys ecosystems
d) Always harmful
Answer: b) Maintains population balance
Explanation: Controls prey populations and maintains biodiversity.
Q41. Which curve represents exponential growth?
a) S-shaped
b) J-shaped
c) Bell-shaped
d) Straight line
Answer: b) J-shaped
Explanation: Exponential growth produces J-shaped curve.
Q42. Which population attribute is NOT a property of an individual?
a) Age distribution
b) Mortality
c) Natality
d) Sex ratio
Answer: a) Age distribution
Explanation: Age structure is a population attribute, not an individual trait.
Q43. Population growth is maximum at
a) Initial lag phase
b) Exponential phase
c) Stationary phase
d) Decline phase
Answer: b) Exponential phase
Explanation: Growth rate is highest when resources are abundant.
Q44. The ecological principle of competitive exclusion states
a) Two species can coexist in same niche
b) One species will eliminate the other
c) Both species always benefit
d) Neither species is affected
Answer: b) One species will eliminate the other
Explanation: Gause’s principle: no two species can occupy same niche indefinitely.
Q45. Which of the following shows parasitism?
a) Algae and fungus in lichen
b) Mistletoe on mango tree
c) Orchid on mango tree
d) Honeybee on flower
Answer: b) Mistletoe on mango tree
Explanation: Mistletoe is a partial stem parasite.
Q46. Ecological equivalents are
a) Same species in different regions
b) Different species in same habitat performing same function
c) Identical niches across globe
d) Two organisms in competition
Answer: b) Different species in same habitat performing same function
Explanation: Example: desert cat in India and puma in America.
Q47. Commensalism example is
a) Orchid on mango tree
b) Sea anemone and clownfish
c) Tapeworm in humans
d) Cuckoo in crow’s nest
Answer: b) Sea anemone and clownfish
Explanation: Clownfish gets shelter, anemone unaffected.
Q48. The age pyramid of a declining population is
a) Triangular
b) Rectangular
c) Inverted
d) Bell-shaped
Answer: c) Inverted
Explanation: Inverted pyramid shows low birth rate, more older individuals.
Q49. The type of survivorship curve in oysters is
a) Type I
b) Type II
c) Type III
d) Type IV
Answer: c) Type III
Explanation: Many young die early; few survive to adulthood.
Q50. Which of the following is a keystone predator?
a) Tiger in forest
b) Starfish in rocky shore
c) Lion in savanna
d) Snake in grassland
Answer: b) Starfish in rocky shore
Explanation: Starfish predation maintains species diversity in intertidal zones.
🟢 Part 3: Ecology and Environment – Organisms and Populations (Q51–Q75)
Q51. Which interaction is “+ –”?
a) Predation
b) Competition
c) Mutualism
d) Commensalism
Answer: a) Predation
Explanation: Predator benefits (+), prey is harmed (–).
Q52. In which biome do annual plants dominate due to short life cycles?
a) Desert
b) Grassland
c) Tundra
d) Rainforest
Answer: a) Desert
Explanation: Annuals survive drought by completing life cycle quickly in wet season.
Q53. The interaction between fig tree and wasp is
a) Commensalism
b) Mutualism
c) Amensalism
d) Competition
Answer: b) Mutualism
Explanation: Wasp pollinates fig flowers and gets food/shelter.
Q54. In logistic growth, population growth is maximum at
a) N = 0
b) N = K
c) N = K/2
d) N > K
Answer: c) N = K/2
Explanation: Growth rate peaks at half the carrying capacity.
Q55. Age pyramid with broad base indicates
a) Declining population
b) Expanding population
c) Stable population
d) Extinct population
Answer: b) Expanding population
Explanation: More young individuals → high birth rate → population growth.
Q56. The population attribute that affects genetic structure is
a) Natality
b) Sex ratio
c) Mortality
d) Immigration
Answer: b) Sex ratio
Explanation: Male–female ratio affects mating and genetic diversity.
Q57. The highest mortality in early stages is shown by which survivorship curve?
a) Type I
b) Type II
c) Type III
d) Type IV
Answer: c) Type III
Explanation: Many offspring die early (e.g., oysters, fish, plants).
Q58. Exponential population growth equation is
a) dN/dt = rN
b) dN/dt = rN(K – N)/K
c) dN/dt = K – N
d) dN/dt = N – r
Answer: a) dN/dt = rN
Explanation: J-shaped exponential growth depends on intrinsic rate of increase (r).
Q59. Desert plants minimize water loss by
a) Broad leaves
b) CAM photosynthesis and thick cuticle
c) Shallow roots only
d) Deciduous leaves
Answer: b) CAM photosynthesis and thick cuticle
Explanation: CAM reduces transpiration; waxy cuticle prevents water loss.
Q60. Which of the following is an example of ectotherms?
a) Birds
b) Mammals
c) Amphibians and reptiles
d) Humans
Answer: c) Amphibians and reptiles
Explanation: Their body temperature varies with external environment.
Q61. Which ecological interaction reduces interspecific competition?
a) Niche differentiation
b) Predation
c) Parasitism
d) Amensalism
Answer: a) Niche differentiation
Explanation: Species minimize competition by occupying different niches.
Q62. The carrying capacity of an environment depends on
a) Birth rate only
b) Availability of resources
c) Mortality alone
d) Migration alone
Answer: b) Availability of resources
Explanation: Food, space, and water limit maximum sustainable population size.
Q63. Thermal stratification is observed in
a) Desert
b) Lakes
c) Tundra
d) Grassland
Answer: b) Lakes
Explanation: Different temperature layers form in deep water bodies.
Q64. An organism conforming to environmental conditions is called
a) Regulator
b) Conformer
c) Migrant
d) Hibernator
Answer: b) Conformer
Explanation: Conformers cannot regulate; 99% of animals and plants are conformers.
Q65. Population size remains constant in
a) Exponential growth
b) Logistic growth
c) Zero growth phase
d) Decline phase
Answer: c) Zero growth phase
Explanation: Natality and mortality are equal, leading to equilibrium.
Q66. Seasonal migration of birds is an adaptation for
a) Avoiding predators
b) Favorable breeding and feeding conditions
c) Increasing lifespan
d) Competition
Answer: b) Favorable breeding and feeding conditions
Explanation: Birds migrate to suitable habitats seasonally.
Q67. Which of the following interactions is beneficial to both species?
a) Predation
b) Mutualism
c) Parasitism
d) Amensalism
Answer: b) Mutualism
Explanation: Both species gain (e.g., pollination, mycorrhiza).
Q68. Population density can be expressed as
a) Number per unit area
b) Biomass per unit area
c) Both a and b
d) None
Answer: c) Both a and b
Explanation: Density = numerical (per unit area/volume) or biomass-based.
Q69. Which equation represents logistic growth?
a) dN/dt = rN
b) dN/dt = rN(K – N)/K
c) dN/dt = r/K
d) dN/dt = N – K
Answer: b) dN/dt = rN(K – N)/K
Explanation: Logistic growth accounts for carrying capacity (K).
Q70. Which population attribute is NOT measurable in an individual?
a) Mortality
b) Natality
c) Age distribution
d) Birth rate
Answer: c) Age distribution
Explanation: Age distribution applies to population, not individuals.
Q71. Which adaptation helps polar animals resist cold?
a) Long ears
b) Thick fur and blubber
c) CAM photosynthesis
d) Short lifespan
Answer: b) Thick fur and blubber
Explanation: Insulation conserves heat in extreme cold.
Q72. Allen’s Rule states that
a) Animals in colder regions have shorter ears and limbs
b) Animals in deserts have long ears
c) Large size in cold climate
d) Small body in warm climate
Answer: a) Animals in colder regions have shorter ears and limbs
Explanation: Minimizes heat loss in cold regions.
Q73. Which survivorship curve do birds often show?
a) Type I
b) Type II
c) Type III
d) Type IV
Answer: b) Type II
Explanation: Constant mortality rate throughout life is typical of birds.
Q74. Which curve represents logistic population growth?
a) J-shaped
b) S-shaped
c) Bell-shaped
d) Linear
Answer: b) S-shaped
Explanation: Logistic growth produces sigmoidal curve due to carrying capacity.
Q75. Which of the following is NOT a density-dependent factor?
a) Food competition
b) Predation
c) Disease
d) Earthquake
Answer: d) Earthquake
Explanation: Earthquakes affect populations irrespective of density.
🟢 Part 4: Ecology and Environment – Organisms and Populations (Q76–Q100)
Q76. Which is an example of ectothermic regulation?
a) Sweating in humans
b) Sun basking in lizards
c) Shivering in birds
d) Blubber in seals
Answer: b) Sun basking in lizards
Explanation: Ectotherms regulate temperature by behavior, e.g., basking.
Q77. Intraspecific competition is usually more severe than interspecific because
a) Same species require same resources
b) Different niches exist for different species
c) Predators are involved
d) Genetic variations are less
Answer: a) Same species require same resources
Explanation: Members of same species have identical needs, so competition is intense.
Q78. Which of the following is an adaptation of desert animals?
a) Thick blubber
b) Estivation
c) Counter-current heat exchange
d) Antifreeze proteins
Answer: b) Estivation
Explanation: Desert animals undergo summer sleep to avoid high temperature and water loss.
Q79. The density of a population is influenced by
a) Natality
b) Mortality
c) Immigration and emigration
d) All of these
Answer: d) All of these
Explanation: All four factors determine population size and density.
Q80. Which of the following is an example of commensalism?
a) Lichen
b) Cuckoo and crow
c) Barnacles on whales
d) Mistletoe on mango
Answer: c) Barnacles on whales
Explanation: Barnacles get transport, whale unaffected.
Q81. The fundamental niche of a species is
a) Actual space occupied with competitors
b) Full range of conditions without competitors
c) Limited by mutualism only
d) Same as realized niche
Answer: b) Full range of conditions without competitors
Explanation: Realized niche is narrower due to competition and other interactions.
Q82. Which is a K-selected species?
a) Bacteria
b) Housefly
c) Elephant
d) Cockroach
Answer: c) Elephant
Explanation: K-strategists are large, long-lived, with few offspring and parental care.
Q83. Which factor is abiotic?
a) Predation
b) Competition
c) Temperature
d) Parasitism
Answer: c) Temperature
Explanation: Abiotic = non-living factors like temperature, water, and soil.
Q84. If birth rate equals death rate, population will
a) Increase
b) Decline
c) Remain stable
d) Fluctuate wildly
Answer: c) Remain stable
Explanation: Zero growth occurs when natality = mortality.
Q85. Which is an example of amensalism?
a) Penicillium secreting penicillin inhibiting bacteria
b) Orchid on mango
c) Lion preying on deer
d) Birds feeding on insects stirred by cattle
Answer: a) Penicillium secreting penicillin inhibiting bacteria
Explanation: One harmed, other unaffected.
Q86. An age pyramid with narrow base and wide top indicates
a) Expanding population
b) Declining population
c) Stable population
d) Fluctuating population
Answer: b) Declining population
Explanation: Low birth rate, more old individuals.
Q87. Which survivorship curve is typical of humans?
a) Type I
b) Type II
c) Type III
d) Type IV
Answer: a) Type I
Explanation: Most survive to old age; mortality increases in later stages.
Q88. Seasonal migration of fish like salmon is for
a) Escape from predators
b) Spawning (breeding)
c) Avoiding cold
d) Food only
Answer: b) Spawning (breeding)
Explanation: Salmon migrate upstream for reproduction.
Q89. Which equation describes exponential population growth?
a) dN/dt = rN
b) dN/dt = rN(K–N)/K
c) dN/dt = N/K
d) dN/dt = rK
Answer: a) dN/dt = rN
Explanation: Exponential growth occurs with unlimited resources.
Q90. The natural place of an organism is called
a) Habitat
b) Niche
c) Biome
d) Community
Answer: a) Habitat
Explanation: Habitat = physical environment where an organism lives.
Q91. Which interaction is shown by mycorrhizal fungi with plant roots?
a) Amensalism
b) Mutualism
c) Parasitism
d) Commensalism
Answer: b) Mutualism
Explanation: Fungus provides minerals and water; plant provides sugars.
Q92. What is aestivation?
a) Winter sleep
b) Summer sleep
c) Daily dormancy
d) Migration
Answer: b) Summer sleep
Explanation: Aestivation helps escape high heat and desiccation.
Q93. Which type of competition is most intense?
a) Interspecific
b) Intraspecific
c) Amensalism
d) Commensalism
Answer: b) Intraspecific
Explanation: Same species need identical resources → strongest competition.
Q94. Survivorship curve of many fishes and invertebrates is
a) Type I
b) Type II
c) Type III
d) Type IV
Answer: c) Type III
Explanation: High mortality in early life; few survive to adulthood.
Q95. Which type of growth occurs when resources are limited?
a) Exponential
b) Logistic
c) Irregular
d) Geometric
Answer: b) Logistic
Explanation: Logistic growth levels off at carrying capacity, forming S-curve.
Q96. Which adaptation allows kangaroo rats to survive without drinking water?
a) Storing water in body
b) High metabolic water from seeds
c) Large water-filled bladders
d) Drinking dew
Answer: b) High metabolic water from seeds
Explanation: Obtain water from oxidation of food; conserve via concentrated urine.
Q97. Which is an example of brood parasitism?
a) Honeybee and flower
b) Cuckoo laying eggs in crow’s nest
c) Mistletoe on mango
d) Tiger hunting deer
Answer: b) Cuckoo laying eggs in crow’s nest
Explanation: Host rears parasitic young at its own cost.
Q98. Which law states that “no two species can occupy the same niche indefinitely”?
a) Gause’s competitive exclusion principle
b) Allen’s rule
c) Bergmann’s rule
d) Liebig’s law of minimum
Answer: a) Gause’s competitive exclusion principle
Explanation: One species will eliminate the other from identical niche.
Q99. Which attribute of population shows number of males and females?
a) Sex ratio
b) Age structure
c) Density
d) Natality
Answer: a) Sex ratio
Explanation: Ratio of males to females in a population.
Q100. The intrinsic rate of natural increase (r) is maximum when
a) Birth rate > Death rate
b) Birth rate = Death rate
c) Birth rate < Death rate
d) Population is at K
Answer: a) Birth rate > Death rate
Explanation: r is positive and maximum when births exceed deaths.
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