Q1. Match the organisms with their growth parameters:
Column-I
Column-II
A. Norway rat (r)
(I) 0.12
B. Flour beetle (r)
(II) 0.015
C. Human India 1981 (r)
(III) 0.0205
Correct Answer: (a)
The intrinsic rate of natural increase (r) for Norway rat is 0.015; for flour beetle it is 0.12; and for human population in India (1981) it was 0.0205. These values reflect their respective reproductive potentials.
Q2. Assertion: Resource partitioning allows species to avoid competition.
Reason: Species choose different times for feeding or different foraging patterns.
Correct Answer: (a)
Resource partitioning is the division of limited resources among species to reduce competition. This can involve differential use of resources in space, time, or food type. The reason gives examples of such partitioning (e.g., different feeding times), thus correctly explaining how competition is avoided.
Q3. Which statement is true for the 'Intrinsic rate of natural increase (r)'? (i) It is a measure of the inherent potential of a population to grow. (ii) It is used to assess impacts of biotic/abiotic factors. (iii) It is the difference between birth and death rates (b-d).
Correct Answer: (a)
r reflects the population's maximum growth potential under ideal conditions. It can be used to compare effects of environmental factors, and it is indeed the per capita difference between birth and death rates (b – d). All statements are correct.
Q4. Assertion: Ectoparasites live inside the host body.
Reason: The life cycles of endoparasites are more complex because of their extreme specialisation.
Correct Answer: (a)
Ectoparasites live on the external surface of the host (e.g., ticks, lice), not inside. The assertion is therefore false. However, the reason is true: endoparasites (living inside) often have complex life cycles with multiple hosts and specialised adaptations, reflecting their extreme specialisation.
Q5. Match the following for interspecific interactions:
Combination
Interaction
A. (–, –)
(I) Competition
B. (+, –)
(II) Predation/Parasitism
C. (+, 0)
(III) Commensalism
Correct Answer: (a)
Competition harms both species (–,–); predation/parasitism benefits one and harms the other (+,–); commensalism benefits one and leaves the other unaffected (+,0). This is the standard classification of interspecific interactions.
Q6. Which organisms breed only once in their lifetime?
Correct Answer: (b)
Pacific salmon and bamboo are classic examples of semelparous organisms, which reproduce only once and then die. Most birds and mammals breed multiple times (iteroparous). Oysters also produce many offspring repeatedly.
Q7. If 8 new lotus plants are added to a current population of 20 through reproduction, the birth rate is:
Correct Answer: (b)
Birth rate is the number of new individuals produced per individual per unit time. Here, 8 offspring are produced by 20 individuals, so 8/20 = 0.4 offspring per lotus plant. This rate measures the per capita reproductive output of the population.
Q8. Who is revered as the Father of Ecology in India?
Correct Answer: (b)
Ramdeo Misra is widely recognised as the pioneer of ecological research and education in India. He established the first postgraduate course in ecology and inspired generations of ecologists. His contributions laid the foundation for modern Indian ecology.
Q9. In 1981, the 'r' value for the human population in India was:
Correct Answer: (b)
India’s human population had an r value of 0.0205 in 1981, indicating a moderate growth rate. This value is used to project population changes and assess the impact of demographic policies. It is lower than that of many insects but higher than some larger mammals.
Q10. Which of the following are correct regarding 'Predation'? (i) Predators keep prey populations under control. (ii) Introduction of exotic species can lead to invasiveness due to lack of natural predators. (iii) Predators help in maintaining species diversity.
Correct Answer: (a)
Predators regulate prey numbers, prevent dominance, and contribute to species diversity. Exotic species often become invasive when their natural predators are absent in the new environment. Thus, all three statements are correct.
Q11. Match the following for evolutionary theorists:
A. Darwin
(I) Use and disuse of organs
B. Lamarck
(II) Natural selection
C. Hugo de Vries
(III) Saltation
Correct Answer: (a)
Darwin proposed natural selection; Lamarck advocated use and disuse inheritance; Hugo de Vries proposed mutation theory (saltation). These are distinct evolutionary concepts proposed by these scientists.
Q12. Assertion: Parasites tend to co-evolve with their hosts.
Reason: Hosts evolve mechanisms for resisting the parasite, and parasites evolve to counteract them.
Correct Answer: (a)
Co-evolution is a reciprocal evolutionary change between interacting species. In host-parasite systems, hosts evolve defenses (e.g., immune responses) while parasites evolve counter-adaptations (e.g., antigenic variation). This dynamic leads to a tight evolutionary relationship, making the reason the correct explanation for the assertion.
Q13. Assertion: Natural selection operates at the population level to evolve desired traits.
Reason: Individual organisms have to cope with a changed environment, but they do not evolve.
Correct Answer: (a)
Natural selection acts on the genetic variation present in populations, leading to evolutionary changes over generations. Individuals cannot evolve; they can only respond to environmental changes through physiological or behavioral adjustments. Thus, the population is the unit of evolution, and the reason correctly explains why.
Q14. Match the following for prey defense:
A. Cryptic colouration
(I) Camouflage
B. Distasteful chemical
(II) Monarch Butterfly
C. Poisonous nature
(III) Avoidance by predators
Correct Answer: (a)
Cryptic coloration is camouflage; Monarch butterfly has distasteful chemicals; poisonous nature deters predators. These are diverse prey defense mechanisms that reduce predation risk.
Q15. Which of the following is true for 'Carrying Capacity (K)'? (i) It is the maximum number a habitat can support. (ii) Beyond this, no further growth is possible. (iii) it leads to the formation of a sigmoid curve.
Correct Answer: (a)
Carrying capacity is the maximum sustainable population size. When N reaches K, growth ceases, producing the plateau of the sigmoid curve. All three statements correctly describe K.
Q16. Regarding 'Mutualism', identify the correct statements: (i) Both interacting species benefit. (ii) Mycorrhizae are associations between fungi and plant roots. (iii) The fig tree provides food for wasp larvae.
Correct Answer: (a)
Mutualism benefits both partners. Mycorrhizae are mutualistic fungus-root associations. In fig-wasp mutualism, the fig provides a site for wasp oviposition and larvae food. All statements are correct.
Q17. Exponential growth results in which type of curve when plotted against time?
Correct Answer: (c)
Exponential growth assumes unlimited resources, leading to a constant per capita growth rate. The population size multiplies rapidly, producing a J-shaped curve when plotted over time. S-shaped (logistic) curves occur when resources become limiting.
Q18. Which factor might contribute more significantly to population growth than birth rates in a newly colonised habitat?
Correct Answer: (c)
In a newly colonised habitat, immigration can be a major source of population increase, sometimes exceeding local births. As individuals from surrounding areas move in, the population grows rapidly. Mortality and emigration would reduce growth, while carrying capacity limits growth.
Q19. Match the following for mutualism:
A. Lichens
(I) Fungi and roots of higher plants
B. Mycorrhizae
(II) Fungus and alga
C. Fig and Wasp
(III) Pollination and oviposition
Correct Answer: (a)
Lichens are associations of fungus and alga; mycorrhizae are fungus-root associations; fig and wasp mutualism involves pollination and oviposition. Each is a distinct mutualistic relationship.
Q20. Assertion: Calotropis is avoided by cattle and goats.
Reason: The plant produces highly poisonous cardiac glycosides.
Correct Answer: (a)
Calotropis (milkweed) contains cardiac glycosides that are toxic to vertebrates. Cattle and goats instinctively avoid browsing on it because these compounds can disrupt heart function. The chemical defense is the direct cause of avoidance, so the reason correctly explains the assertion.
Q21. In the equation Nt+1 = Nt + [(B + I) – (D + E)], 'I' stands for:
Correct Answer: (b)
In this population growth equation, B = births, I = immigration, D = deaths, and E = emigration. Immigration adds new individuals from outside, contributing to population increase. The other options are not part of this standard notation.
Q22. Match the following for plant life cycles:
A. Pacific salmon fish
(I) Breed only once
B. Bamboo
(II) Breed only once
C. Most birds
(III) Breed many times
Correct Answer: (a)
Pacific salmon and bamboo are semelparous, breeding only once and then dying. Most birds are iteroparous, breeding multiple times over their lifetime. Thus, A and B match with I, C with III.
Q23. Match the following for commensalism:
Column-I (Species A)
Column-II (Species B)
A. Orchid epiphyte
(I) Mango tree
B. Barnacles
(II) Whale
C. Cattle Egret
(III) Grazing Cattle
D. Sea Anemone
(IV) Clown Fish
Correct Answer: (a)
Orchids grow on mango trees (epiphyte); barnacles attach to whales; cattle egrets feed on insects disturbed by grazing cattle; sea anemones provide shelter to clown fish. All are classic examples of commensalism where one partner benefits, the other is unaffected.
Q24. Identify correct facts for 'Amoeboid Movement' (Unit VIII intro / Page 2): (i) Effected by pseudopodia. (ii) Cytoskeletal elements like microfilaments are involved. (iii) Seen in macrophages and leucocytes.
Correct Answer: (a)
Amoeboid movement involves pseudopodia driven by actin microfilaments. This type of movement is seen in amoebae, macrophages, and leucocytes. All three statements are correct.
Q25. Correct statements for 'Ramdeo Misra' include: (i) He establishing teaching and research in ecology at BHU. (ii) He formulated the first postgraduate course in ecology in India. (iii) He supervised over 50 Ph.D. scholars.
Correct Answer: (a)
Ramdeo Misra pioneered ecology education in India, started the first postgraduate course at Banaras Hindu University, and mentored many students. All three statements are accurate.
Q26. Nature’s limit for supporting a maximum possible number of a species in a habitat is called:
Correct Answer: (c)
Carrying capacity (K) is the maximum population size that a habitat can sustain indefinitely given the available resources. Beyond K, resources become insufficient, causing population decline. Growth rate and intrinsic rate are measures of change, not limits.
Q27. Match the following for commensalism (epiphytes):
A. Orchid
(I) Epiphyte
B. Mango tree
(II) Support (Host)
Correct Answer: (a)
Orchids grow as epiphytes on mango trees, using them only for physical support without harming the tree. This is a commensal relationship: orchid benefits, mango tree is unaffected.
Q28. Assertion: Growth of a population is ultimately limited by the carrying capacity of the environment.
Reason: In nature, resources are finite and eventually become limiting.
Correct Answer: (a)
Carrying capacity (K) is defined by the finite availability of resources such as food, water, and space. As population approaches K, resource scarcity slows growth and eventually halts it. Thus, the reason correctly explains why carrying capacity limits population growth.
Q29. Assertion: A species whose distribution is restricted to a small area may expand its range if a competitor is removed.
Reason: This phenomenon is known as 'competitive release'.
Correct Answer: (a)
Competitive release occurs when a species expands its realized niche or geographic range after the removal of a competing species. The assertion describes this exact scenario, and the reason gives the correct term for it. Hence, the reason correctly explains the observed expansion.
Q30. Assertion: Parasites may render the host more vulnerable to predation.
Reason: Parasites make the host physically weak.
Correct Answer: (a)
Parasites drain energy and nutrients from their hosts, often causing weakness, reduced mobility, or behavioural changes. Such weakened hosts are easier targets for predators. Therefore, the reason directly explains why parasitism can increase predation risk.
Q31. Match the following for competition in barnacles:
A. Superior competitor
(I) Balanus
B. Inferior competitor
(II) Chathamalus
Correct Answer: (a)
In Connell's experiments, Balanus outcompeted Chathamalus in the intertidal zone, leading to the latter's restricted distribution. Balanus is the superior competitor; Chathamalus is the inferior.
Q32. Assertion: Co-evolution is tight in the fig tree and wasp relationship.
Reason: A given fig species can be pollinated only by its ‘partner’ wasp species and no other.
Correct Answer: (a)
Fig trees and their pollinating wasps have a highly specific mutualistic relationship; each fig species is pollinated by a single wasp species. This one-to-one dependency drives co-evolution, where changes in one partner select for reciprocal changes in the other. The reason correctly explains why co-evolution is tight in this system.
Q33. A population attribute that expresses the proportion of males and females is:
Correct Answer: (c)
Sex ratio is the relative number of males and females in a population. It is an important demographic characteristic that affects mating and reproductive potential. Natality and mortality refer to birth and death rates, while age pyramid shows age distribution.
Q34. Assertion: Predation is nature's way of transferring energy to higher trophic levels.
Reason: Tigers and sparrows are both examples of predators.
Correct Answer: (b)
Predation is indeed a key mechanism for energy transfer in ecosystems, as predators consume prey and convert biomass into energy for themselves. However, simply stating that tigers and sparrows are predators does not explain the ecological process of energy transfer. The reason provides examples but not the underlying mechanism, so it is true but not the correct explanation.
Q35. Identify the correct phylum/group being described: (i) They are phytophagous (feed on plant sap). (ii) Nearly 25 per cent of all these fall into this category. (iii) They are predators for plants.
Correct Answer: (a)
Insects are the group where about 25% are phytophagous (plant-eating). They are herbivores, not predators of plants (predators usually kill animals). Thus, 'Insects' is the correct answer.
Q36. Assertion: The orchid Ophrys employs 'sexual deceit' for pollination.
Reason: One petal of its flower resembles the female of a specific bee species.
Correct Answer: (a)
Ophrys orchids mimic the appearance and scent of female bees to attract male bees. The males attempt to mate with the flower (pseudocopulation), thereby picking up or depositing pollen. This deceitful strategy ensures pollination without offering any reward, and the reason explains the mechanism.
Q37. Match the following for age pyramids:
A. Expanding
(I) Pre-reproductive > Reproductive
B. Stable
(II) Pre-reproductive = Reproductive
C. Declining
(III) Pre-reproductive < Reproductive
Correct Answer: (a)
An expanding population has a high proportion of young (pre-reproductive > reproductive); stable has equal proportions; declining has more reproductive and post-reproductive individuals (pre-reproductive < reproductive). These relationships define the pyramid shapes.
Q38. Select correct statements for 'Niche' (implied in interaction sections): (i) No two species can co-exist indefinitely if they compete for the same limiting resources. (ii) This is Gause's Competitive Exclusion Principle.
Correct Answer: (a)
The competitive exclusion principle states that two species cannot coexist indefinitely on the same limiting resource; one will outcompete the other. This principle is attributed to Gause. Both statements are correct.
Q39. Match the following for history of man settlement:
A. 18,000 years ago
(I) Cave Art
B. 10,000 years ago
(II) Agriculture
Correct Answer: (a)
Cave art dates back to about 18,000 years ago. Agriculture began around 10,000 years ago during the Neolithic revolution. These are key milestones in human cultural evolution.
Q40. Assertion: Endoparasites have complex life cycles.
Reason: They are extremely specialized in their site of living inside the host body.
Correct Answer: (a)
Endoparasites live within their hosts, often in specific organs or tissues, which requires intricate adaptations to survive. Their complex life cycles frequently involve multiple hosts and various developmental stages. The extreme specialization in site of living drives the evolution of these complex cycles, so the reason correctly explains the assertion.
Q41. Identify the correct statements regarding 'Competition': (i) It is a potent force in organic evolution. (ii) Abingdon tortoise became extinct due to goats. (iii) Closely related species always exclude each other.
Correct Answer: (a)
Competition drives evolutionary changes (character displacement). The Abingdon tortoise was driven to extinction by competition with introduced goats. However, closely related species can coexist through resource partitioning; they do not always exclude each other. So (i) and (ii) are correct, (iii) is false.
Q42. Assertion: Lichens represent an intimate mutualistic relationship between a fungus and an alga.
Reason: The alga provides energy-yielding carbohydrates to the fungus.
Correct Answer: (a)
Lichens are classical examples of mutualism: the photosynthetic alga (or cyanobacterium) produces carbohydrates via photosynthesis, which are used by the fungus; in return, the fungus provides a protected environment and nutrients. The reason correctly explains why this association is mutualistic.
Q43. The 'r' value for the Norway rat is:
Correct Answer: (c)
The intrinsic rate of natural increase (r) for the Norway rat is 0.015. This value indicates its inherent capacity to grow under optimal conditions. Different species have characteristic r values; for example, the flour beetle has a higher r of 0.12.
Q44. Match the following for liver fluke:
A. Intermediate host 1
(I) Snail
B. Intermediate host 2
(II) Fish
Correct Answer: (a)
Liver fluke (Fasciola) has a complex life cycle: the first intermediate host is a snail, and the second is a fish. The final host is a vertebrate (e.g., sheep). This is a classic example of a parasite with multiple hosts.
Q45. Assertion: In interference competition, resources need not be limiting for competition to occur.
Reason: The feeding efficiency of one species might be reduced due to the inhibitory presence of the other.
Correct Answer: (a)
Interference competition occurs when individuals directly interact, for example, by aggressive behaviour, even when resources are abundant. The mere presence of one species can reduce the other's feeding efficiency. This contrasts with exploitative competition, where resources are directly consumed. Thus, the reason correctly explains that resource limitation is not a prerequisite.
Q46. Verhulst-Pearl Logistic Growth results in which type of curve?
Correct Answer: (b)
The logistic growth model, described by Verhulst and Pearl, produces a sigmoid (S-shaped) curve. It features an initial lag phase, followed by rapid exponential growth, and finally a plateau at carrying capacity. This realistic model accounts for resource limitation.
Q47. Match the following for competition examples:
A. Abingdon tortoise
(I) Goats in Galapagos
B. Balanus and Chathamalus
(II) Rocky sea coasts of Scotland
C. Warblers
(III) Resource partitioning
Correct Answer: (a)
Abingdon tortoise became extinct due to competition with introduced goats; Balanus and Chathamalus are barnacles studied by Connell on Scottish rocky shores; warblers show resource partitioning by foraging in different parts of trees. These are well-known competition examples.
Q48. Match the interactions with their names:
Column-I (Combination)
Column-II (Name)
A. (–, 0)
(I) Mutualism
(II) Amensalism
B. (+, 0)
(III) Commensalism
C. (+, +)
(IV) Parasitism
D. (+, –)
Correct Answer: (a)
Amensalism is (–,0); commensalism is (+,0); mutualism is (+,+); parasitism is (+,–). These are the correct pairings based on the effect on each species.
Q49. Which of the following is correct? (i) All locomotions are movements. (ii) Evolution is a stochastic process. (iii) Humans use limbs for both posture change and locomotion.
Correct Answer: (a)
All locomotion is a form of movement; evolution involves chance events (genetic drift) and natural selection (stochastic); human limbs serve both posture and movement. All statements are correct.
Q50. Assertion: Human beings are able to digest cellulose.
Reason: Cellulose breakdown is assisted by methanogens in the rumen of cattle.
Correct Answer: (a)
Humans lack the enzyme cellulase and cannot digest cellulose; it passes through the digestive tract as dietary fibre. The reason correctly states that methanogens in cattle rumen help break down cellulose, but this is irrelevant to human digestion. Thus, assertion is false, reason is true.
Q51. Regarding 'Population Attributes', which statements are correct? (i) An individual has births and deaths, but a population has birth and death rates. (ii) Populations have a sex ratio. (iii) An individual is either male or female, but a population is measured in percentages of both.
Correct Answer: (a)
All three statements are correct. Birth rate and death rate are population-level parameters; sex ratio is a population attribute; and the proportion of males and females is meaningful only at the population level. These are fundamental characteristics studied in population ecology.
Q52. Identify correct features of the 'Biogas Plant' (Unit VIII context / Figure 8.8): (i) Concrete tank 10-15 feet deep. (ii) Slurry of dung is fed. (iii) Floating cover is placed over the slurry.
Correct Answer: (a)
A typical biogas plant has a deep concrete tank, receives animal dung slurry, and has a floating cover to collect the gas. All features are correct as per standard design.
Q53. A population density measured in terms of percent cover or biomass is preferred when:
Correct Answer: (b)
When individuals vary greatly in size, counting numbers can be misleading. For example, a large banyan tree and many small carrot grass plants may have similar biomass or cover. Percent cover or biomass gives a better measure of ecological importance than mere count.
Q54. Assertion: Logistic growth is considered a more realistic model in nature.
Reason: Resources for growth for most animal populations are finite and become limiting.
Correct Answer: (a)
In nature, resources such as food, water, and space are rarely unlimited; they eventually become scarce as population increases. Logistic growth incorporates this by including a carrying capacity (K). Therefore, the finite nature of resources is the fundamental reason logistic growth is more realistic than exponential growth.
Q55. Identify correct statements for 'Resource Partitioning': (i) It promotes co-existence rather than exclusion. (ii) MacArthur showed this in warblers. (iii) Species choose different foraging patterns.
Correct Answer: (a)
Resource partitioning allows competing species to coexist by dividing resources. MacArthur's study of warblers demonstrated this: they foraged in different parts of trees. All three statements are correct.
Q56. Which level of biological organisation is basically concerned with interactions among organisms and between the organism and its physical environment?
Correct Answer: (b)
Ecology is the branch of biology that studies the interactions of organisms with each other and with their abiotic environment. It encompasses population, community, and ecosystem levels. Cellular or genetic levels focus on internal mechanisms, not environmental interactions.
Q57. The Monarch butterfly is distasteful to its predator (bird) because of a chemical acquired during which stage?
Correct Answer: (c)
Monarch caterpillars feed on milkweed plants (Asclepias) that contain cardiac glycosides. These toxic compounds are stored in the caterpillar and retained through metamorphosis into the adult butterfly, making it unpalatable to birds. The chemical is acquired only during the larval (caterpillar) feeding stage.
Q58. Assertion: The tiger census is often based on pug marks and fecal pellets.
Reason: It is very difficult to estimate huge population sizes by direct counting.
Correct Answer: (a)
Direct counting of tigers is impractical due to their large home ranges and low densities. Instead, indirect signs like pug marks and scat are used as reliable proxies for population size. The difficulty in direct counting is precisely why these indirect methods are employed, making the reason the correct explanation.
Q59. Regarding 'Parasitism', select the correct statements: (i) Parasites tend to be host-specific. (ii) They often have complex life cycles with intermediate hosts. (iii) Brood parasitism is seen in the crow laying eggs in the koel's nest.
Correct Answer: (a)
Parasites are often host-specific and may have complex life cycles (e.g., liver fluke). However, brood parasitism involves the koel (cuckoo) laying eggs in the crow's nest, not the other way round. Thus (i) and (ii) are correct, (iii) is false.
Q60. The 'r' value for the flour beetle is:
Correct Answer: (c)
The flour beetle (Tribolium) has an r value of 0.12, reflecting its relatively high reproductive potential. This contrasts with the Norway rat (0.015) and human population in India (0.0205). r values help compare growth potentials across species.
Q61. Select correct statements for 'Co-evolution': (i) Seen in the fig-wasp relationship. (ii) Seen in the orchid-bee relationship. (iii) Evolutions of the flower and its pollinator species are tightly linked.
Correct Answer: (a)
Co-evolution involves reciprocal genetic changes in interacting species. Fig-wasp and orchid-bee are classic examples where flower and pollinator traits evolve in response to each other. All three statements are correct.
Q62. Ramdeo Misra helped establish the National Committee for Environmental Planning and Coordination in which year?
Correct Answer: (b)
The National Committee for Environmental Planning and Coordination was set up in 1972, following the Stockholm Conference. Ramdeo Misra’s advocacy and efforts were instrumental in its formation. This committee was a landmark step in India's environmental governance.
Q63. Regarding 'Haplodiploid sex-determination' (Unit VII context): (i) Males have half the number of chromosomes than females. (ii) Seen in honey bees. (iii) Males produce sperms by mitosis.
Correct Answer: (a)
In haplodiploidy, males are haploid, females diploid. This occurs in honey bees and other Hymenoptera. Males produce gametes by mitosis (no meiosis) because they are haploid. All statements are correct.
Q64. Which is true for the 'Ganga Action Plan'? (i) Initiated to save major rivers from pollution. (ii) Proposed building a large number of sewage treatment plants.
Correct Answer: (a)
The Ganga Action Plan was launched to reduce pollution in the Ganges and other rivers by setting up sewage treatment plants. Both statements describe its objectives and strategies.
Q65. Match the growth curve variables:
Symbol
Meaning
A. N
(I) Intrinsic rate of natural increase
B. r
(II) Population density
C. K
(III) Carrying capacity
Correct Answer: (a)
N represents population density (number per unit area); r is the intrinsic rate of natural increase; K is the carrying capacity of the environment. These symbols are standard in population ecology equations.
Q66. Identify the correct statements for 'Population Growth': (i) Natality and Immigration increase population density. (ii) Mortality and Emigration decrease population density. (iii) Under normal conditions, immigration is the most important factor.
Correct Answer: (a)
Natality (births) and immigration add individuals, increasing density; mortality and emigration remove individuals, decreasing density. Under normal conditions, births and deaths are usually the dominant factors, not immigration. Hence (i) and (ii) are correct, (iii) is false.
Q67. Match the natural selection patterns (Figure 6.8 / 11.3 context):
Pattern
Description
A. Stabilising
(I) Peak shifts in one direction
B. Directional
(II) Two peaks form
C. Disruptive
(III) Peak gets higher and narrower
Correct Answer: (a)
Stabilising selection favours the mean phenotype and reduces variation (peak becomes higher and narrower). Directional selection shifts the mean phenotype in one direction. Disruptive selection favours both extremes, creating two peaks.
Q68. An interaction where both species benefit is called:
Correct Answer: (b)
Mutualism is an interspecific interaction where both participating species gain benefits (+,+). Examples include lichens (fungus + alga) and mycorrhizae (fungus + plant roots). Commensalism benefits one, competition harms both, and predation benefits one at the expense of the other.
Q69. Assertion: Mycorrhizae are associations between fungi and the roots of higher plants.
Reason: It is a classic example of commensalism.
Correct Answer: (a)
Mycorrhizae are indeed mutualistic associations between fungi and plant roots, benefiting both partners (fungus obtains carbohydrates, plant gets enhanced mineral and water uptake). The reason claims it is commensalism (+,0), which is incorrect. Hence assertion is true, reason is false.
Q70. In amensalism, one species is ______ and the other is ______.
Correct Answer: (b)
Amensalism is a (‒,0) interaction: one species is harmed while the other remains unaffected. For instance, the antibiotic-producing fungus Penicillium inhibits bacteria without benefiting directly from them. This is distinct from competition, parasitism, or commensalism.
Q71. Assertion: Competition can occur between totally unrelated species.
Reason: Flamingoes and fishes in S. American lakes compete for their common food (zooplankton).
Correct Answer: (a)
Competition does not require taxonomic relatedness; it depends on resource overlap. Flamingoes (birds) and fishes (vertebrates) share the same zooplankton prey in some South American lakes, leading to interspecific competition. This example directly supports the assertion, making the reason a valid explanation.
Q72. The essence of biological understanding is to know how organisms interact with other organisms and physical habitats as a group, known as:
Correct Answer: (b)
The interactions among organisms and with their abiotic surroundings give rise to organised systems like populations and communities. These groupings behave as integrated wholes, not just isolated individuals. Ecology focuses on these organised wholes to understand the functioning of nature.
Q73. Which of the following is correct regarding 'Age Pyramids'? (i) The shape reflects the growth status of the population. (ii) Expanding populations have more post-reproductive individuals. (iii) Stable populations have equal proportions of pre-reproductive and reproductive individuals.
Correct Answer: (a)
The shape of an age pyramid indeed indicates growth status. However, expanding populations have more pre-reproductive (young) individuals, not post-reproductive. Stable populations have roughly equal proportions of pre-reproductive and reproductive individuals. Thus, (i) and (iii) are correct.
Q74. Regarding 'Exponential Growth', which statements are true? (i) Resources (food and space) must be unlimited. (ii) The curve is J-shaped. (iii) The equation is dN/dt = rN.
Correct Answer: (a)
Exponential growth assumes unlimited resources, leading to a J-shaped curve, and the differential equation dN/dt = rN accurately describes it. All three statements are true and characterize the exponential model.
Q75. Which of the following are adaptations of 'Parasites'? (i) Loss of unnecessary sense organs. (ii) Presence of adhesive organs or suckers. (iii) High reproductive capacity.
Correct Answer: (a)
Parasites often lose organs not needed in their host environment (e.g., sense organs), develop adhesive structures to attach, and produce many offspring to ensure transmission. All are adaptations to the parasitic mode of life.
Q76. Match the parasite type with example:
Type
Example
A. Ectoparasite
(I) Liver fluke
B. Endoparasite
(II) Ticks on dogs
C. Parasitic plant
(III) Cuscuta
D. Brood parasite
(IV) Koel (Cuckoo)
Correct Answer: (a)
Ticks are ectoparasites (external); liver fluke is an endoparasite (internal); Cuscuta (dodder) is a parasitic plant; koel is a brood parasite that lays eggs in crow nests. Each type is correctly matched with a representative example.
Q77. Match the following for population growth models:
A. J-shaped
(I) Exponential
B. S-shaped (Sigmoid)
(II) Logistic
Correct Answer: (a)
Exponential growth produces a J-shaped curve when resources are unlimited. Logistic growth gives an S-shaped (sigmoid) curve because resources become limiting and the population approaches carrying capacity.
Q78. The age distribution of a population is graphically represented by:
Correct Answer: (b)
An age pyramid is a graphical representation of the proportion of individuals in different age groups (pre-reproductive, reproductive, post-reproductive). It reveals the growth status of the population. Bell, sigmoid, and J-shaped curves depict growth patterns, not age structure.
Q79. Regarding 'Life History Variation', which are correct? (i) Organisms evolve towards the most efficient reproductive strategy. (ii) Pacific salmon breeds only once. (iii) Pelagic fishes produce many small-sized offspring.
Correct Answer: (a)
Life history traits evolve to optimize reproductive success. Pacific salmon are semelparous (breed once). Pelagic fishes produce many small eggs to increase offspring survival in the open ocean. All statements are correct.
Q80. Assertion: Brood parasitism is seen in the Koel and the Crow.
Reason: The Koel lays eggs in the crow's nest and lets the crow incubate them.
Correct Answer: (a)
Brood parasitism is a form of parasitism where the parasite (koel) lays its eggs in the nest of another bird (crow) and relies on the host to raise its young. This is exactly the behavior described, and the reason provides the specific interaction between the two species, correctly explaining the assertion.
Q81. Assertion: In a sigmoid curve, the last phase is an asymptote.
Reason: This happens when the population density reaches the carrying capacity.
Correct Answer: (a)
The logistic growth curve (sigmoid) plateaus at the carrying capacity (K) of the environment. At this stage, the population size stabilizes and the curve approaches a horizontal asymptote. Thus, the asymptote is a direct consequence of reaching K, making the reason the correct explanation.
Q82. Match the following for mutualistic pollinators:
A. Fig tree
(I) Wasp
B. Ophrys (Orchid)
(II) Specific Bee
Correct Answer: (a)
Fig trees are pollinated exclusively by fig wasps (Agaonidae). Ophrys orchids are pollinated by specific bee species through pseudocopulation. These are classic examples of specialized mutualisms.
Q83. Match the following for parasite characteristics:
A. Adhesive organs
(I) To cling on to host
B. Loss of digestive system
(II) Living in free meals
Correct Answer: (a)
Parasites have adhesive organs (suckers, hooks) to attach to their host. Some endoparasites have lost their digestive system because they absorb nutrients directly from the host's body. These are adaptations to their parasitic lifestyle.
Q84. If 4 fruitflies in a laboratory population of 40 died in a week, the death rate is:
Correct Answer: (a)
Death rate is the number of deaths per individual per unit time. In this case, 4 deaths out of 40 individuals gives 4/40 = 0.1 deaths per fruitfly per week. This rate helps monitor population decline due to mortality.
Q85. Which of the following processes contributes to a decrease in population density?
Correct Answer: (c)
Emigration is the permanent movement of individuals out of a population, which reduces its size. In contrast, natality (birth) and immigration (arrival) increase population density. Mortality (death) also decreases density, but emigration is the correct option here.
Q86. Which of the following is correct regarding 'Commensalism'? (i) One species benefits, the other is neither harmed nor benefited. (ii) Orchid on a mango branch is an example. (iii) The clown fish and sea anemone interaction is another example.
Correct Answer: (a)
Commensalism is defined as (+,0) interaction. Orchids on trees and clown fish with anemones are classic examples. All three statements are correct.
Q87. Assertion: Gause’s ‘Competitive Exclusion Principle’ states that closely related species cannot co-exist indefinitely if resources are limiting.
Reason: The competitively inferior one will be eliminated eventually.
Correct Answer: (a)
Gause's principle (also called the competitive exclusion principle) asserts that two species competing for the same limiting resource cannot coexist permanently; one will outcompete the other and drive it to local extinction. The elimination of the inferior competitor is the logical outcome, so the reason correctly explains the principle.
Q88. Match the following for population growth:
Variable
Definition
A. Natality
(I) Number of births
B. Mortality
(II) Number of deaths
C. Immigration
(III) Individuals coming into habitat
D. Emigration
(IV) Individuals leaving habitat
Correct Answer: (a)
Natality is the birth rate; mortality is the death rate; immigration refers to individuals entering a population; emigration is individuals leaving. These definitions are fundamental to understanding population dynamics.
Q89. The invasive weed introduced into Australia in the 1920s that caused havoc was:
Correct Answer: (c)
The prickly pear cactus (Opuntia) was introduced to Australia and became a serious pest, covering vast areas of agricultural land. Biological control using the cactus moth (Cactoblastis cactorum) eventually brought it under control. Water hyacinth and Parthenium are also invasive but in different contexts.
Q90. Match the following for plant chemical defenses:
A. Cardiac glycosides
(I) Calotropis
B. Nicotine, Caffeine, Opium
(II) Commercial extraction / Defense
Correct Answer: (a)
Calotropis produces cardiac glycosides as a defense against herbivores. Other alkaloids like nicotine, caffeine, and opium are also plant defenses but are also commercially extracted. Thus, A matches with I, B with II.
Q91. The starfish Pisaster is an important predator in which community?
Correct Answer: (c)
Pisaster ochraceus is a keystone predator in rocky intertidal communities of the American Pacific coast. By preying on mussels, it maintains species diversity and prevents competitive exclusion. Its removal drastically alters the community structure.
Q92. Assertion: In an age pyramid, an expanding population has a broad base.
Reason: It indicates a high proportion of pre-reproductive individuals.
Correct Answer: (a)
An age pyramid with a broad base signifies that a large fraction of the population is in the pre-reproductive (young) age group. Such a population will grow rapidly in the future as these young individuals enter reproductive age. The broad base is a direct visual indicator of a high proportion of young, so the reason correctly explains the assertion.
Q93. Match the following for the history of man (intro pages):
A. Homo habilis
(I) 650-800cc
B. Homo erectus
(II) 900cc
C. Neanderthal man
(III) 1400cc
Correct Answer: (a)
Homo habilis had a brain capacity of about 650-800 cc; Homo erectus about 900 cc; Neanderthal man about 1400 cc. These values reflect the increasing brain size during human evolution.
Q94. Match the biological defences in Column-I with the organisms in Column-II:
Column-I (Defence)
Column-II (Organism)
A. Thorns
(I) Monarch Butterfly
B. Distasteful chemical
(II) Acacia, Cactus
C. Cardiac glycosides
(III) Calotropis
Correct Answer: (a)
Thorns are physical defences found in Acacia and cactus; Monarch butterfly stores distasteful chemicals from its food plants; Calotropis produces cardiac glycosides that are toxic. These defences help organisms avoid predation.
Q95. Identify the correct statements for 'Logistic Growth': (i) It is called Verhulst-Pearl Logistic Growth. (ii) A population starts with a lag phase. (iii) It eventually reaches an asymptote when N = K.
Correct Answer: (a)
The logistic growth model is named after Verhulst and Pearl. It begins with a lag phase, followed by rapid growth, and ends at an asymptote at carrying capacity (K). All statements are correct.
Q96. The tiger census in our national parks is often based on:
Correct Answer: (c)
Direct counting of tigers is difficult due to their elusive nature and large territories. Instead, indirect evidence like pug marks and fecal pellets are used to estimate population size. This method provides reliable estimates of tiger presence and abundance.
Q97. Assertion: The clown fish gets protection by living among sea anemone tentacles.
Reason: Sea anemone tentacles have stinging cells that stay predators away.
Correct Answer: (a)
Clown fish are immune to the stinging nematocysts of sea anemones and find shelter among their tentacles. The anemone's stinging cells deter predators, providing a safe haven for the clown fish. This mutualistic relationship benefits both, and the reason directly explains how the clown fish gains protection.
Q98. Regarding the 'Law of Dominance' (Mendel's laws mentioned in intro): (i) Characters are controlled by factors. (ii) Factors occur in pairs. (iii) One member of a dissimilar pair dominates the other.
Correct Answer: (a)
Mendel's law of dominance states that traits are controlled by factors (genes) that occur in pairs, and in a heterozygous pair, one allele is dominant over the other. All statements correctly describe the law.
Q99. Assertion: Predators in nature are described as 'prudent'.
Reason: If a predator is too efficient and overexploits its prey, the prey might become extinct and the predator will follow.
Correct Answer: (a)
Predators that overexploit their prey risk causing prey extinction, which would ultimately lead to their own demise due to lack of food. Thus, natural selection favours predators that are not too efficient—they are 'prudent'. This principle explains why predator-prey systems often reach a sustainable equilibrium.
Q100. Match the population interactions in Column-I with the symbols in Column-II:
Column-I (Interaction)
Column-II (Symbols)
A. Mutualism
(I) +, –
B. Competition
(II) +, +
C. Predation
(III) –, –
D. Commensalism
(IV) +, 0
Correct Answer: (a)
Mutualism benefits both (+,+); competition harms both (–,–); predation benefits one and harms the other (+,–); commensalism benefits one without affecting the other (+,0). This matching is standard for interspecific interactions.