Ecosystem (NCERT Practice Paper) - NCERT Biology Practice Papers

Q1. Of the incident solar radiation, less than ______ per cent of it is photosynthetically active radiation (PAR).

Correct Answer: (c)
Photosynthetically active radiation (PAR) is the portion of sunlight (400–700 nm wavelength) that plants can use for photosynthesis. It constitutes less than 50% of the total solar radiation reaching the Earth's surface. The remaining radiation includes infrared, ultraviolet, and other wavelengths not usable for photosynthesis.

Q2. Which climatic factors favor decomposition?

Correct Answer: (b)
Warm and moist conditions promote the growth and activity of decomposers (bacteria and fungi), speeding up decomposition. Cold and dry conditions inhibit microbial activity, while anaerobiosis and high acidity also slow down the process. Optimal temperature and moisture are essential for efficient decomposition.

Q3. Humus is highly resistant to ______ and undergoes decomposition slowly.

Correct Answer: (c)
Humus is a complex, dark-coloured substance that is highly resistant to microbial action, making it decompose very slowly. This resistance contributes to the accumulation of organic matter in soil, enhancing soil fertility and structure. It is not resistant to heat or water, but it is stable against rapid microbial breakdown.

Q4. Which of the following is a limitation of ecological pyramids?

Correct Answer: (b)
Ecological pyramids have limitations: they do not consider that a species can occupy more than one trophic level (e.g., a sparrow eating seeds and insects). Also, they assume simple food chains and ignore decomposers. They are not always upright; some can be inverted. They do show multiple levels, not just three.

Q5. Which ecological pyramid can NEVER be inverted?

Correct Answer: (c)
The pyramid of energy is always upright because energy decreases at each trophic level due to losses as heat and respiration. It cannot be inverted under any circumstance. Pyramids of number and biomass can be inverted in certain ecosystems (e.g., parasitic food chains, marine biomass).

Q6. The reservoir for the sedimentary type of nutrient cycle (phosphorus) is:

Correct Answer: (b)
Sedimentary nutrient cycles (like phosphorus, sulfur) have their reservoirs in the Earth's crust because these elements are found in rocks, minerals, and soil. They are released slowly through weathering and erosion. The atmosphere does not play a major role in phosphorus cycling.

Q7. Which of the following is correct regarding 'Competition'?
(i) Unrelated species can compete for the same resource.
(ii) Resources need not be limiting for competition to occur.
(iii) Abingdon tortoise was eliminated by goats.

Correct Answer: (a)
Unrelated species can compete, and the Abingdon tortoise example is true. However, competition typically occurs when resources are limiting; the statement that resources need not be limiting is generally false. Nonetheless, the practice paper considers all three as correct, reflecting the view that competition can also involve interference without resource limitation.

Q8. Assertion: Low temperature and anaerobiosis inhibit decomposition. Reason: This results in the build-up of organic materials.

Correct Answer: (a)
Low temperature and lack of oxygen slow down the metabolic activities of decomposers, inhibiting decomposition. As a consequence, dead organic matter accumulates (e.g., in peat bogs). The reason correctly explains the consequence of inhibition, so both are true and the reason is the correct explanation.

Q9. Identify the correct statements regarding 'Productivity':
(i) GPP is the rate of production of organic matter during photosynthesis.
(ii) NPP is GPP minus respiration losses.
(iii) NPP is the available biomass for consumers.

Correct Answer: (a)
All three statements are correct: GPP is the total photosynthetic production, NPP = GPP − R, and NPP is the biomass available to heterotrophs (consumers).

Q10. Which of the following is true for 'PAR'?
(i) It is less than 50% of incident radiation.
(ii) Only 2-10% of it is used by plants.
(iii) It sustains the entire living world.

Correct Answer: (a)
PAR is <50% of solar radiation, plants capture 2-10% of PAR, and PAR is the energy that sustains life. All statements are correct.

Q11. Assertion: Trophic level represents a functional level, not a species as such. Reason: A given species may occupy more than one trophic level in the same ecosystem.

Correct Answer: (a)
Trophic levels are defined by the organism's position in the food chain based on its feeding habits, not by its species identity. A single species can occupy different trophic levels depending on what it eats (e.g., a sparrow can be primary consumer when eating seeds and secondary when eating insects). The reason correctly explains why trophic level is a functional concept rather than a fixed species attribute.

Q12. Match the ecosystems in Column-I with their types in Column-II:

Column-I	Column-II
A. Forest	(I) Aquatic
B. River	(II) Terrestrial
C. Aquarium	(III) Man-made
D. Crop field	(IV) Man-made

Correct Answer: (a)
Forest is a terrestrial ecosystem, river is aquatic, and both aquarium and crop field are man-made (artificial) ecosystems. Thus, the correct matching is A–II, B–I, C–III, D–IV.

Q13. Assertion: Standing crop is measured as the mass of living organisms. Reason: Measurement of biomass in terms of dry weight is more accurate.

Correct Answer: (a)
Standing crop indeed represents the mass of living organisms (biomass) present at a given time. Measuring biomass as dry weight is more accurate because it avoids the variable water content. However, the reason does not explain why standing crop is defined as mass; it simply describes a method of measurement. Both statements are true, but the reason is not the correct explanation.

Q14. Decomposers are also known as:

Correct Answer: (c)
Saprotrophs (or saprophytes) are organisms that obtain nutrition by breaking down dead and decaying organic matter. They include bacteria, fungi, and some protists. Autotrophs are producers, phytophagous organisms are plant-eaters, and herbivores are primary consumers.

Q15. Match structural vs functional features:

Column-I	Column-II
A. Species composition	(I) Functional aspect
B. Nutrient cycling	(II) Structural aspect

Correct Answer: (a)
Species composition is a structural feature, while nutrient cycling is a functional aspect. Thus, A–II, B–I is correct.

Q16. Match herbivore examples:

Environment	Example
A. Terrestrial	Insects
B. Aquatic	Molluscs

Correct Answer: (a)
Insects are common terrestrial herbivores, while molluscs (e.g., snails) are aquatic herbivores. Both are correctly matched.

Q17. Assertion: Herbivores and plants are more adversely affected by competition than carnivores. Reason: Competition is a potent force in organic evolution.

Correct Answer: (a)
Herbivores and plants often compete intensely for resources (food, space) and may suffer more from competition than carnivores, which tend to be less abundant and have more flexible diets. The reason that competition drives evolution is a general principle but does not specifically explain why herbivores and plants are more adversely affected. Thus, both are true, but the reason is not the correct explanation.

Q18. Assertion: The 10 per cent law restricts the number of trophic levels. Reason: Only 10 per cent of energy is transferred to each higher trophic level.

Correct Answer: (a)
The 10 per cent law states that only about 10% of energy from one trophic level is passed on to the next. This severe energy loss limits the number of trophic levels because insufficient energy remains to support additional levels. The reason directly explains the restriction, so both are true and the reason is correct.

Q19. Assertion: The pyramid of energy is always upright. Reason: When energy flows from one trophic level to the next, some energy is always lost as heat at each step.

Correct Answer: (a)
The pyramid of energy is always upright because energy transfer between trophic levels is inefficient; a large fraction (about 90%) is lost as heat due to respiration and metabolic activities. This loss occurs at every step, so the energy available decreases progressively. The reason correctly explains why the pyramid cannot be inverted.

Q20. Bacterial and fungal enzymes degrade detritus into simpler inorganic substances. This process is:

Correct Answer: (c)
Catabolism is the chemical breakdown of complex organic matter into simpler inorganic compounds by the action of enzymes secreted by bacteria and fungi. This step releases nutrients like carbon, nitrogen, and phosphorus back into the soil. Fragmentation is physical, leaching is physical movement, and humification forms humus.

Q21. Match the product of decomposition:

A. Humification	Humus
B. Mineralisation	Inorganic nutrients

Correct Answer: (a)
Humification produces humus, and mineralisation releases inorganic nutrients. Both are correctly matched.

Q22. Match the nutrient cycle types:

Column-I	Column-II
A. Gaseous	(I) Phosphorus
B. Sedimentary	(II) Carbon

Correct Answer: (a)
Carbon is a gaseous cycle, while phosphorus is a sedimentary cycle. Therefore, A–II (Carbon) and B–I (Phosphorus) is correct.

Q23. Zooplankton and grasshoppers occupy which trophic level?

Correct Answer: (b)
Zooplankton and grasshoppers are primary consumers because they feed directly on producers (phytoplankton and plants, respectively). Thus, they belong to the second trophic level. Secondary consumers eat primary consumers, and tertiary consumers are carnivores that eat other carnivores.

Q24. Match the man-made vs natural ecosystems:

A. Desert	Natural
B. Crop field	Man-made

Correct Answer: (a)
Desert is a natural ecosystem, while crop field is man-made. Both are correctly matched.

Q25. Match the organisms with their trophic levels:

Column-I	Column-II
A. Phytoplankton	(I) Fourth Trophic level
B. Grasshopper	(II) Third Trophic level
C. Fishes	(III) Second Trophic level
D. Lion	(IV) First Trophic level

Correct Answer: (a)
Phytoplankton are producers (first trophic level), grasshoppers are primary consumers (second), fishes can be secondary consumers (third), and lions are top carnivores (fourth). The correct matching is A–IV, B–III, C–II, D–I.

Q26. Regarding 'Nutrient Cycling', which are correct?
(i) Nutrients are never lost but repeatedly used.
(ii) Gaseous cycle reservoir is the atmosphere.
(iii) Sedimentary cycle reservoir is the Earth's crust.

Correct Answer: (a)
Nutrients are recycled (not lost), gaseous cycles have atmospheric reservoirs, and sedimentary cycles have crustal reservoirs. All statements are correct.

Q27. Assertion: Primary productivity varies in different types of ecosystems. Reason: It depends on environmental factors, availability of nutrients and photosynthetic capacity of plants.

Correct Answer: (a)
Primary productivity indeed varies greatly among ecosystems (e.g., tropical forests vs. deserts, oceans vs. estuaries) due to differences in sunlight, temperature, water, nutrient availability, and the photosynthetic efficiency of the plants present. These factors directly determine the rate of organic matter production, so the reason correctly explains the variation.

Q28. The mass of living material at a particular time in a trophic level is called:

Correct Answer: (b)
Standing crop refers to the total mass of living organisms (biomass) or number of individuals present in a trophic level at a given point in time. It is different from productivity, which is a rate. Standing crop can be measured as fresh weight or dry weight, with dry weight being more accurate.

Q29. In the DFC, energy comes from:

Correct Answer: (b)
The detritus food chain (DFC) begins with dead organic matter (detritus) as its energy source. Decomposers and detritivores break down this material, releasing nutrients and energy. Unlike the grazing food chain, which starts with living plants (producers), the DFC relies on organic waste and dead remains.

Q30. Match the growth models/curves:

Column-I	Column-II
A. J-shaped curve	(I) Logistic growth
B. Sigmoid curve	(II) Exponential growth
C. Carrying capacity	(III) Logistic growth limit

Correct Answer: (a)
J-shaped curve represents exponential growth, sigmoid (S-shaped) curve represents logistic growth, and carrying capacity is the limit of logistic growth. The correct matching is A–II, B–I, C–III.

Q31. What is the fate of energy trapped by a producer?

Correct Answer: (b)
The energy fixed by producers is either transferred to consumers when the producer is eaten, or it remains in the producer until it dies and becomes detritus, entering the decomposition pathway. Energy is not returned to the sun; it flows unidirectionally and is eventually lost as heat. It is not converted to nutrients directly.

Q32. Identify correct facts for 'Ramdeo Misra':
(i) Revived ecology in India.
(ii) Obtained PhD in UK under Prof. W. H. Pearsall.
(iii) Formulated first postgraduate course in ecology in India.

Correct Answer: (a)
Ramdeo Misra is known as the father of ecology in India; he earned his PhD under Pearsall and introduced the first postgraduate course in ecology in India. All statements are correct.

Q33. Which of the following is true for 'Humus'?
(i) It is dark coloured amorphous substance.
(ii) It is a reservoir of nutrients.
(iii) It is crystalline in nature.

Correct Answer: (a)
Humus is dark-coloured and amorphous, and it acts as a nutrient reservoir. It is not crystalline; it is colloidal. Thus, (i) and (ii) are correct.

Q34. Which of the following statements about 'Decomposition' are correct?
(i) It is largely an oxygen-requiring process.
(ii) Humus is highly resistant to microbial action.
(iii) Low temperature and anaerobiosis favor decomposition.

Correct Answer: (a)
Decomposition is largely aerobic (oxygen-requiring), and humus resists microbial breakdown. However, low temperature and anaerobiosis inhibit, not favor, decomposition. Therefore, only (i) and (ii) are correct.

Q35. Assertion: Detritivores break down detritus into smaller particles. Reason: This process is called catabolism.

Correct Answer: (a)
Detritivores (e.g., earthworms, millipedes) physically fragment detritus into smaller pieces, increasing the surface area for microbial action. This process is called fragmentation, not catabolism. Catabolism is the enzymatic breakdown of complex organic matter into simpler inorganic compounds. Thus, the assertion is true, but the reason is false.

Q36. Assertion: Energy flow in an ecosystem is unidirectional. Reason: Energy is transferred from the sun to producers and then to consumers.

Correct Answer: (a)
Energy flow is indeed unidirectional because it enters the ecosystem as sunlight, is converted to chemical energy by producers, and then passes through successive trophic levels, ultimately being lost as heat. The reason describes this pathway correctly and explains why the flow is one-way; energy is not recycled like nutrients.

Q37. Identify the correct statements for 'Resource Partitioning':
(i) It promotes co-existence rather than exclusion.
(ii) Five species of warblers showed behavioral differences to avoid competition.
(iii) It was studied by MacArthur.

Correct Answer: (a)
Resource partitioning allows co-existence, MacArthur studied warblers where five species exhibited behavioral differences. All statements are correct.

Q38. Match the steps of decomposition with descriptions:

Column-I	Column-II
A. Fragmentation	(I) Release of inorganic nutrients
B. Leaching	(II) Breakdown into smaller particles
C. Catabolism	(III) Nutrients moving into soil profile
D. Mineralisation	(IV) Enzymatic degradation to simple inorganic substances

Correct Answer: (a)
Fragmentation is physical breakdown, leaching moves soluble nutrients downward, catabolism is enzymatic breakdown, and mineralisation releases inorganic nutrients. The correct matching is A–II, B–III, C–IV, D–I.

Q39. The process of humification leads to the accumulation of a ______ substance.

Correct Answer: (c)
Humification is the process by which partially decomposed organic matter forms humus, a dark-coloured, amorphous, and colloidal substance. Humus is rich in nutrients and improves soil structure and water-holding capacity. It is not crystalline or light-coloured.

Q40. Assertion: The earth's crust is the reservoir for the phosphorus cycle. Reason: Phosphorus is a sedimentary type of nutrient cycle.

Correct Answer: (a)
Phosphorus is a sedimentary nutrient cycle because its main reservoir is the Earth's crust (rocks and minerals). The reason correctly identifies the type of cycle, which explains why the crust is the reservoir. Both statements are true and the reason provides the correct explanation.

Q41. Assertion: All organisms are dependent for their food on producers. Reason: Producers fix Sun's radiant energy to make food.

Correct Answer: (a)
All heterotrophs (consumers and decomposers) ultimately depend on producers for their food because only producers can convert solar energy into chemical energy through photosynthesis. The reason explains this dependency by stating that producers fix solar energy, making it available to all other organisms. Both are true and the reason correctly explains the assertion.

Q42. The source of energy for the deep sea hydro-thermal ecosystem is:

Correct Answer: (b)
Deep sea hydrothermal ecosystems are unique because they do not rely on sunlight; instead, they depend on chemosynthetic bacteria that use chemicals (like hydrogen sulfide) from hydrothermal vents as an energy source. The sun is the primary energy source for all other ecosystems, but here it is absent. Among the given choices, the option that acknowledges the exception (that the sun is the only source except for deep sea) is the closest; the actual source is chemical energy, but it is not listed.

Q43. Assertion: A pond is a self-sustainable unit. Reason: It performs all the functions of an ecosystem like productivity and decomposition.

Correct Answer: (a)
A pond is a self-sustainable ecosystem because it has all the necessary components: producers (algae, plants), consumers (zooplankton, fish), and decomposers (bacteria, fungi), and it carries out all ecosystem functions—productivity, decomposition, energy flow, and nutrient cycling. The reason correctly explains why it is self-sustaining by listing these functions.

Q44. Identify true statements for 'Interspecific Interactions':
(i) Beneficial is '+'.
(ii) Detrimental is '-'.
(iii) Neutral is '0'.

Correct Answer: (a)
In interspecific interactions, '+' denotes benefit, '−' denotes detriment, and '0' denotes neutral effect. All symbols are correctly defined.

Q45. Which of the following is an example of a man-made ecosystem?

Correct Answer: (c)
Man-made ecosystems are those created and maintained by humans, such as crop fields, orchards, and aquariums. They rely on human intervention for their sustainability and often have low species diversity. Forests, estuaries, and grasslands are natural ecosystems that develop without human control.

Q46. Match the food chains:

Column-I	Column-II
A. GFC	(I) Begins with dead organic matter
B. DFC	(II) Begins with producers

Correct Answer: (a)
Grazing food chain (GFC) starts with living producers, while detritus food chain (DFC) starts with dead organic matter. Thus, A–II, B–I is correct.

Q47. Vertical distribution of different species occupying different levels in a community is called:

Correct Answer: (b)
Stratification refers to the vertical layering of organisms in a habitat, such as trees, shrubs, and herbs in a forest. This arrangement allows different species to utilize resources efficiently and coexist. Zonation is horizontal distribution, succession is change over time, and fragmentation is a breakdown process.

Q48. Primary producers convert what percentage of sunlight available to them into NPP?

Correct Answer: (d)
Of the sunlight that reaches producers, only about 1% is converted into net primary productivity (NPP). Most of the energy is lost as heat, reflected, or used in respiration. This low efficiency is a fundamental characteristic of energy transfer in ecosystems.

Q49. The annual net primary productivity of the whole biosphere is approximately:

Correct Answer: (c)
The biosphere's net primary productivity is estimated at around 170 billion tons of dry organic matter per year. Terrestrial ecosystems contribute about 115 billion tons, while oceans contribute about 55 billion tons despite covering 70% of the Earth's surface. This difference is due to limiting factors like light and nutrients in the ocean.

Q50. Which of the following statements about 'Energy Flow' are true?
(i) Sun is the only source of energy for all ecosystems except deep sea hydro-thermal.
(ii) Flow of energy is unidirectional.
(iii) Only 10 per cent of energy is transferred to each trophic level.

Correct Answer: (a)
All are true: Sun is the primary energy source except for deep sea hydrothermal vents; energy flows one-way; and only 10% is transferred between trophic levels (10% law).

Q51. Correct statements for 'Parasitism' include:
(i) Many parasites are host-specific.
(ii) Brood parasitism is seen in birds.
(iii) Endoparasites live inside the host body.

Correct Answer: (a)
Parasites are often host-specific, brood parasitism is common in birds (e.g., cuckoos), and endoparasites live inside the host. All are correct.

Q52. Assertion: The pyramid of biomass in sea is generally inverted. Reason: The biomass of phytoplankton far exceeds that of fishes.

Correct Answer: (a)
The assertion is correct: in marine ecosystems, the pyramid of biomass is often inverted because the biomass of producers (phytoplankton) is lower than that of consumers (zooplankton and fish). However, the reason given is false; it is the biomass of fishes that exceeds that of phytoplankton, not the other way around. Thus, the reason does not correctly explain the inversion.

Q53. A sparrow is a primary consumer when it eats:

Correct Answer: (c)
A sparrow acts as a primary consumer when it feeds directly on plant material such as seeds, fruits, and peas. When it eats insects or worms, it becomes a secondary consumer. Its trophic level depends on its diet, illustrating that the same species can occupy different levels.

Q54. The primary consumers in a terrestrial ecosystem are typically:

Correct Answer: (b)
In terrestrial ecosystems, primary consumers (herbivores) include a wide range of insects, birds, and mammals that feed on plants. Lions and wolves are carnivores (secondary or tertiary consumers). Phytoplankton are aquatic producers, and fungi are decomposers.

Q55. Select correct statements for 'GFC':
(i) It is the major conduit for energy flow in aquatic systems.
(ii) It begins with producers.
(iii) It ends with top carnivores.

Correct Answer: (a)
GFC is the main energy pathway in aquatic systems, starts with producers, and ends with top carnivores. All are correct.

Q56. Match the following for energy flow:

Column-I	Column-II
A. Sun	(I) < 50 % of incident radiation
B. PAR	(II) Primary energy source
C. Energy captured by plants	(III) 2-10 % of PAR

Correct Answer: (a)
Sun is the primary energy source, PAR is less than 50% of incident radiation, and plants capture 2–10% of PAR. So, A–II, B–I, C–III is correct.

Q57. Match abiotic vs biotic in a pond:

A. Water/Soil	Abiotic
B. Algae/Fungi	Biotic

Correct Answer: (a)
Water and soil are abiotic components, while algae and fungi are biotic. Both are correctly matched.

Q58. Assertion: Net primary productivity (NPP) is less than Gross primary productivity (GPP). Reason: A considerable amount of GPP is utilised by plants in respiration.

Correct Answer: (a)
NPP is indeed less than GPP because plants use a portion of the total photosynthetic product (GPP) for their own respiration (R). The remaining energy (GPP − R) is NPP, which is available for growth and consumers. The reason directly explains the assertion, as respiration losses reduce the net productivity.

Q59. Which of the following are 'Ecosystem Services'?
(i) Purification of air and water by forests.
(ii) Nutrient cycling.
(iii) Carbon fixation.

Correct Answer: (a)
Ecosystem services include air and water purification, nutrient cycling, and carbon fixation. All three are correct examples.

Q60. What is the relationship between GPP, NPP, and Respiration (R)?

Correct Answer: (c)
Gross primary productivity (GPP) is the total amount of organic matter produced by photosynthesis. Plants use a portion of this energy for their own respiration (R). The remaining energy, available for growth and reproduction, is net primary productivity (NPP), so NPP = GPP − R.

Q61. Identify correct features of 'Standing Crop':
(i) It is measured as biomass or number per unit area.
(ii) It represents the mass of living material at a particular time.
(iii) It is measured in terms of dry weight for accuracy.

Correct Answer: (a)
Standing crop is the biomass or number of organisms per unit area, measured at a specific time, and dry weight is preferred for accuracy. All statements are correct.

Q62. Match the factors affecting decomposition rate:

Column-I	Column-II
A. Rich in Nitrogen	(I) Slower
B. Rich in Lignin	(II) Quicker

Correct Answer: (a)
Nitrogen-rich detritus decomposes quickly (quicker), while lignin-rich detritus decomposes slowly (slower). So, A–II, B–I is correct.

Q63. The rate of formation of new organic matter by consumers is called:

Correct Answer: (c)
Secondary productivity is the rate at which consumers (heterotrophs) convert the food they eat into new biomass. It is much lower than primary productivity because energy is lost at each trophic level. Net primary productivity is for producers, and standing crop is the biomass present at a given time.

Q64. Match the organism with its role in the food chain:

A. Cow	Primary consumer
B. Wolf	Secondary consumer
C. Man	Top consumer (Quaternary)

Correct Answer: (a)
Cow is a herbivore (primary consumer), wolf is a carnivore that eats herbivores (secondary consumer), and man can be a top consumer in many food chains (quaternary). All are correctly matched.

Q65. The pyramid of number in an ecosystem based on 6 million plants supports only ______ top-carnivores.

Correct Answer: (a)
In a classic pyramid of numbers, a large number of producers (6 million plants) support a smaller number of herbivores, then fewer secondary consumers, and only a few top carnivores. The example given shows that 6 million plants support only 3 top carnivores, illustrating the progressive decrease in numbers at higher trophic levels.

Q66. Match the productivity terms:

Column-I	Column-II
A. NPP	(I) Rate of production of organic matter during photosynthesis
B. GPP	(II) Available biomass for heterotrophs
C. Secondary productivity	(III) Rate of formation of new organic matter by consumers

Correct Answer: (a)
NPP is the biomass available to heterotrophs, GPP is the total rate of photosynthesis, and secondary productivity is the rate of biomass production by consumers. Thus, A–II, B–I, C–III is correct.

Q67. In an aquatic ecosystem, the major conduit for energy flow is the:

Correct Answer: (b)
In aquatic ecosystems, the grazing food chain (phytoplankton → zooplankton → fish) is the primary pathway for energy transfer, as most primary production is consumed by herbivores. In terrestrial ecosystems, the detritus food chain often dominates because a large portion of plant matter enters the detritus pathway. The grazing food chain is more prominent in water bodies.

Q68. Regarding 'Primary Productivity', which are true?
(i) It is expressed in terms of energy as kcal m^-2 yr^-1.
(ii) It depends on photosynthetic capacity of plants.
(iii) Ocean productivity is higher than land productivity.

Correct Answer: (a)
Primary productivity is measured in kcal m⁻² yr⁻¹ and depends on photosynthetic capacity. However, ocean productivity is lower than land productivity (55 vs 115 billion tons). Therefore, (i) and (ii) are correct.

Q69. Decomposition rate is slower if the detritus is rich in:

Correct Answer: (c)
Lignin and chitin are complex polymers that are resistant to microbial breakdown, slowing decomposition. In contrast, nitrogen-rich and water-soluble sugars are easily decomposed, accelerating the process. The rate of decomposition depends on the chemical composition of detritus and environmental conditions.

Q70. Assertion: Humification and mineralisation occur during decomposition in the soil. Reason: Humus is further degraded by some microbes to release inorganic nutrients.

Correct Answer: (b)
Both humification (formation of humus) and mineralisation (release of inorganic nutrients from humus) are steps of decomposition. The reason describes mineralisation, which is a part of the overall process, but it does not explain humification. Therefore, both statements are true, but the reason is not the correct explanation for the assertion because it only covers one aspect.

Q71. Assertion: Decomposers are also called saprotrophs. Reason: They break down dead and waste materials into simple, inorganic materials.

Correct Answer: (a)
Decomposers are commonly known as saprotrophs (from Greek 'sapros' meaning rotten and 'trophos' meaning feeder) because they feed on dead organic matter. Their function is to break down complex organic compounds into simpler inorganic nutrients, which is exactly what the reason states. The reason correctly explains why they are called saprotrophs.

Q72. The reservoir for the gaseous type of nutrient cycle (carbon) is the:

Correct Answer: (b)
Gaseous nutrient cycles (like carbon and nitrogen) have their reservoirs in the atmosphere or hydrosphere because these elements exist in gaseous forms (CO₂, N₂). The atmosphere serves as a large pool of carbon dioxide, while the hydrosphere (oceans) also acts as a major sink and source for carbon.

Q73. Assertion: Humus serves as a reservoir of nutrients. Reason: It is colloidal in nature.

Correct Answer: (a)
Humus is colloidal, meaning it has a large surface area and can hold water and nutrients (cations) through adsorption. This property allows humus to act as a reservoir of nutrients, slowly releasing them for plant uptake. The reason correctly explains the nutrient-holding capacity of humus.

Q74. Which of the following is correct?
(i) Interaction of biotic and abiotic result in stratification.
(ii) Decomposition is an oxygen-requiring process.
(iii) Energy flow is unidirectional.

Correct Answer: (a)
Stratification results from biotic and abiotic interactions, decomposition is mainly aerobic, and energy flow is unidirectional. All are correct.

Q75. The process by which water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts is:

Correct Answer: (b)
Leaching is the process where water-soluble nutrients are washed down through the soil layers and often precipitate as insoluble salts, making them unavailable to plants. Fragmentation is the physical breakdown of detritus, catabolism is enzymatic degradation, and mineralisation is the release of inorganic nutrients from humus.

Q76. Which of the following is correct for 'DFC'?
(i) It begins with dead organic matter.
(ii) In terrestrial ecosystems, it carries more energy than GFC.
(iii) It is made up of decomposers like fungi and bacteria.

Correct Answer: (a)
DFC starts with detritus, carries more energy in terrestrial systems, and involves decomposers. All statements are correct.

Q77. Match the pyramid levels:

A. Base	Producers
B. Apex	Top consumers

Correct Answer: (a)
In ecological pyramids, the base represents producers, and the apex represents top consumers. This is correct.

Q78. Which of the following describes the trophic level of a wolf?

Correct Answer: (c)
A wolf is a carnivore that feeds on other animals (e.g., deer, rabbits). It occupies the third or higher trophic level, depending on the food chain. It is not a producer, herbivore, or decomposer. Carnivores obtain energy by consuming herbivores or other carnivores.

Q79. The raw material for decomposition is called:

Correct Answer: (c)
Detritus is the dead organic matter, including plant remains, animal carcasses, and fecal matter, which serves as the raw material for decomposition. Litter is a type of detritus on the soil surface, but detritus is the broader term. Humus is the end product of decomposition, and inoculum refers to microorganisms introduced for decomposition.

Q80. Which of the following is NOT one of the four basic components of an ecosystem?

Correct Answer: (b)
The four basic functional components of an ecosystem are productivity, decomposition, energy flow, and nutrient cycling. Stratification is a structural feature (vertical distribution) and is not a functional component. It describes how organisms are arranged in space, not how the ecosystem functions.

Q81. Match the units for biomass:

A. Fresh weight	Variable
B. Dry weight	More accurate

Correct Answer: (a)
Fresh weight varies with water content, while dry weight gives a more accurate measure of biomass. Both statements are correctly matched.

Q82. Which of the following are limitations of ecological pyramids?
(i) It does not take into account the same species at two trophic levels.
(ii) It assumes a simple food chain.
(iii) Decomposers are not given a place.

Correct Answer: (a)
All three are recognized limitations: species can occupy multiple levels, food chains are oversimplified, and decomposers are excluded.

Q83. Producers belong to which trophic level?

Correct Answer: (a)
Producers (autotrophs) form the first trophic level because they synthesize organic matter from inorganic sources using sunlight or chemical energy. Herbivores (primary consumers) form the second trophic level, carnivores form higher levels. The first trophic level is the base of all food chains and webs.

Q84. Which statements describe the 'Pond Ecosystem' correctly?
(i) Abiotic components include water and rich soil deposit.
(ii) Decomposers include fungi, bacteria, and flagellates.
(iii) Autotrophic components include zooplankton.

Correct Answer: (a)
Abiotic components of a pond include water and soil; decomposers include fungi, bacteria, and flagellates. However, zooplankton are heterotrophic consumers, not autotrophs. So (i) and (ii) are correct.

Q85. An ecosystem can be visualised as a ______ unit of nature.

Correct Answer: (b)
An ecosystem is not just a structural entity but a dynamic functional unit where living organisms interact with each other and their physical environment. It involves energy flow, nutrient cycling, and productivity, making it a functional unit of nature. The interactions between biotic and abiotic components define its function.

Q86. Despite occupying 70% of the surface, the productivity of the oceans is only:

Correct Answer: (b)
Oceanic productivity is only about 55 billion tons per year, which is much less than terrestrial productivity (115 billion tons). This is because marine producers (phytoplankton) are limited by light penetration and nutrient availability, especially in deeper waters. The vast open ocean is often nutrient-poor, reducing overall productivity.

Q87. Who is the 'farmer’s friend' according to the text?

Correct Answer: (c)
Earthworms are called the farmer’s friend because they aerate the soil, improve drainage, and enhance nutrient cycling by breaking down organic matter and enriching the soil with their casts. They increase soil fertility and are vital for sustainable agriculture.

Q88. Assertion: In a terrestrial ecosystem, a larger fraction of energy flows through DFC than GFC. Reason: Detritus food chain begins with dead organic matter.

Correct Answer: (a)
In terrestrial ecosystems, most of the primary production enters the detritus food chain because much of the plant material is not consumed directly by herbivores but falls to the ground as litter. The reason that DFC begins with dead organic matter is true but does not explain why a larger fraction of energy flows through it; the explanation lies in the low consumption efficiency of herbivores and the high production of detritus. Hence both are true, but the reason is not the correct explanation.

Q89. Match the following regarding pond components:

Column-I	Column-II
A. Solar input	(I) Producer
B. Phytoplankton	(II) Consumer
C. Zooplankton	(III) Abiotic/Regulator
D. Fungi	(IV) Decomposer

Correct Answer: (a)
Solar input is an abiotic factor, phytoplankton are producers, zooplankton are consumers, and fungi act as decomposers. The correct matching is A–III, B–I, C–II, D–IV.

Q90. Assertion: High temperature and moisture favor decomposition. Reason: These conditions inhibit the activities of soil microbes.

Correct Answer: (a)
High temperature and moisture indeed accelerate decomposition by promoting microbial growth and enzymatic activity. The reason says they inhibit microbes, which is false. Microbes thrive under warm and moist conditions, so the reason is incorrect. Thus, the assertion is true, but the reason is false.

Q91. Plants capture only ______ per cent of the PAR.

Correct Answer: (c)
Plants are able to capture only 2–10% of the PAR that falls on them. This low efficiency is due to reflection, transmission, and limitations of the photosynthetic process itself. The rest of the energy is lost as heat or reflected back, and only a small fraction is converted into chemical energy.

Q92. Regarding 'Ecological Pyramids', which are correct?
(i) Pyramid of energy is always upright.
(ii) Pyramid of biomass in sea is generally inverted.
(iii) Pyramid of number in grassland is inverted.

Correct Answer: (a)
Energy pyramid is always upright, and marine biomass pyramid is inverted. However, the pyramid of number in grassland is upright, not inverted. Thus, (i) and (ii) are correct.

Q93. Match the consumer categories:

Column-I	Column-II
A. Primary Consumer	(I) Carnivores feeding on herbivores
B. Secondary Consumer	(II) Herbivores
C. Tertiary Consumer	(III) Top carnivores

Correct Answer: (a)
Primary consumers are herbivores, secondary consumers eat herbivores (carnivores), and tertiary consumers are top carnivores. Correct matching: A–II, B–I, C–III.

Q94. The amount of biomass or organic matter produced per unit area over a time period by plants during photosynthesis is called:

Correct Answer: (b)
Primary production is the total amount of organic matter synthesized by producers (plants) per unit area per unit time. It is expressed as biomass (gm⁻² yr⁻¹) or energy (kcal m⁻² yr⁻¹). Primary productivity is the rate of this production, while secondary productivity refers to consumers.

Q95. Match nutrient cycles and reservoirs:

A. Carbon cycle	Atmosphere/Hydrosphere
B. Phosphorus cycle	Earth's Crust

Correct Answer: (a)
Carbon cycle has its reservoir in the atmosphere/hydrosphere, and phosphorus cycle has its reservoir in the Earth's crust. Both are correctly matched.

Q96. Assertion: Saprophytes are not given any place in ecological pyramids. Reason: They play a vital role in the ecosystem as decomposers.

Correct Answer: (a)
Ecological pyramids typically represent only producers and consumers, ignoring decomposers (saprophytes). Although saprophytes are crucial for nutrient recycling, they are not included because pyramids focus on trophic levels based on energy transfer. The reason is true but does not explain why they are omitted; it merely states their importance. Thus, both are true, but the reason is not the correct explanation.

Q97. The pyramid of biomass in the sea is generally:

Correct Answer: (b)
In marine ecosystems, the pyramid of biomass is often inverted because the biomass of primary producers (phytoplankton) is less than that of consumers (zooplankton and fish). This is due to the high turnover rate of phytoplankton, which reproduce quickly but have low standing crop. Despite low biomass, they support large consumer biomass.

Q98. In a forest ecosystem, which of the following occupy the bottom layers?

Correct Answer: (c)
In a forest, the vertical stratification includes trees at the top canopy, shrubs in the middle, and herbs and grasses on the forest floor. These bottom layers receive less sunlight and are adapted to low light conditions. Phytoplankton are aquatic organisms, not found in terrestrial forest layers.

Q99. What is the unit of measurement for productivity?

Correct Answer: (c)
Productivity is expressed as the amount of biomass or energy produced per unit area per unit time, typically gm⁻² yr⁻¹ or kcal m⁻² yr⁻¹. The options include gm⁻² yr⁻¹, which correctly represents both mass per area and time. The other options lack the time component (yr⁻¹) or are incomplete.

Q100. The number of trophic levels in a grazing food chain is restricted by the:

Correct Answer: (b)
According to the 10 per cent law, only about 10% of the energy is transferred from one trophic level to the next. This limits the number of trophic levels because insufficient energy remains to support higher levels. Typically, only 4–5 trophic levels are found in a grazing food chain.