EcosystemNEET Botany · Class 12 · NCERT Chapter 5

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- Earthworm is a detritivore, consuming and breaking down organic matter.
- Succession starts with pioneer species that colonize bare environments.
- Ecosystem services include pollination, which is crucial for plant reproduction.
- Population growth is influenced by natality, the birth rate of the population.

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The ozone layer is located in the stratosphere, which is the second layer of the Earth's atmosphere. NCERT XII chapter Ecosystem states that the stratosphere contains the ozone layer, which protects the Earth from harmful ultraviolet radiation, so option (c) is correct.

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Anaerobic sludge digesters produce methane, hydrogen sulphide, and carbon dioxide. These gases are byproducts of the anaerobic digestion process, as described in NCERT XII Ecosystem, making option (b) correct.

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- Consumers $\to$ Detritus: Consumers die and become detritus.
- Detritus $\to$ Rock minerals: Decomposition releases minerals back to the soil.
- Rock minerals $\to$ Producers: Plants absorb minerals from the soil.
- Producers $\to$ Litter fall: Plants shed leaves and other organic matter, which becomes litter.

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A scrubber in the exhaust of a chemical industrial plant primarily removes gases like sulphur dioxide. This aligns with the function of scrubbers as described in NCERT XII Ecosystem, making option (a) correct.

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In an ecosystem, only about 10% of energy is transferred from one trophic level to the next. Starting with 20 J at the producer level: $20\times 0.1\times 0.1\times 0.1=0.02\text{J}$ available to the peacock, so option (a) is correct.

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During eutrophication of water bodies, BOD level increases due to rapid growth of microbes. www.vedantu.com 24 Physics

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Increase in concentration of toxic substances in successive trophic level.

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Ecological succession involves gradual and fairly predictable change in the species composition of a given area.

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Lichens do not grow in 𝑆𝑂2 polluted regions therefore they indicate SO2 pollution in air. Phycobionts of lichen are sensitive to 𝑆𝑂2.

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Ley agriculture helps to increase soil fertility and improve the physical texture of soil.

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Cropland ecosystem has same type of crop plants so it has the least genetic diversity.

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The term ecosystem was coined by A.G. Tansley in 1935.

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𝑑𝑁 𝑑𝑡 = 𝑟𝑁 (1 −𝑁 𝐾) 𝑑𝑁 𝑑𝑡 = 𝑟𝑁(1 − 1)= 0

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Lichens are pioneer organisms on bare rocks as they corrode the rocks by secreting enzymes and convert it into soil.

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A river with an inflow of domestic sewage rich in organic waste will reduce the dissolved oxygen (DO) and may result in death of fish due to lack of oxygen. www.vedantu.com 74

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High productive ecosystem are – Tropical rain forest – Coral reef – Estuaries – Sugarcane fields

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The data shows a decrease in biomass from secondary consumers to primary producers, indicating an inverted pyramid of biomass. NCERT XII chapter Ecosystem explains that in an inverted biomass pyramid, the biomass of producers is less than that of consumers, so option (c) is correct.

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Diatoms are the chief producers in the oceans due to their abundance and photosynthetic capability. NCERT XII chapter Ecosystem highlights diatoms as primary producers in marine ecosystems, so option (b) is correct.

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- Eutrophication is caused by nutrient enrichment (i).
- Sanitary landfill is used for waste disposal (iv).
- Snow blindness is caused by UV-B radiation (i).
- Jhum cultivation leads to deforestation (ii).

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Ref. XII NCERT Chapter- 05, Page No. 85-86

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Gross primary productivity (GPP) is the total amount of energy fixed by photosynthesis, while net primary productivity (NPP) is GPP minus the energy used by plants for respiration. Therefore, GPP is always more than NPP, making option (b) correct.

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- Fourth trophic level: Vulture (top carnivore)
- Second trophic level: Rabbit (primary consumer)
- First trophic level: Grass (producer)
- Third trophic level: Crow (secondary consumer)

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In the equation GPP − R = NPP, R represents respiration losses. This is derived from the concept that Net Primary Productivity (NPP) is the Gross Primary Productivity (GPP) minus the energy used by plants for respiration, as explained in NCERT XII chapter Ecosystem. Thus, option (d) is correct.

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The amount of nutrients present in the soil at any given time is referred to as the standing state. NCERT XII chapter Ecosystem defines standing state as the total amount of nutrients in a particular ecosystem at a given time, so option (c) is correct.

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In the exponential growth equation $N_t=N_0{e}^{rt}$, $e$ represents the base of natural logarithms. This is a fundamental constant in mathematics, approximately equal to 2.71828, so option (c) is correct.

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- Nitrococcus converts ammonia to nitrite.
- Rhizobium fixes atmospheric nitrogen to ammonia.
- Thiobacillus is involved in denitrification.
- Nitrobacter converts nitrite to nitrate.

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Dobson units measure the thickness of the ozone layer in the stratosphere. NCERT XII chapter Ecosystem discusses the ozone layer and its measurement, so option (c) is correct.

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Decomposition is the process by which decomposers breakdown complex organic matter into inorganic substances. The rate of decomposition is controlled by chemical composition of detritus and climatic factors. Decomposition is slower if detritus is rich in lignin and chitin and quicker, if detritus is rich in nitrogen and water soluble substances like sugars.

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Habitat loss and fragmentation, over exploitation, alien species invasion and co-extinction are causes for biodiversity loss.

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One of the species in predation gains benefit on the expense of the other. Predators help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species. If a predator is too efficient and overexploits its prey, then the prey might become extinct.

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In predation, one species is benefitted where as the other is harmed. It is (+ –) type of population interaction.

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Phosphorus cycle is a sedimentary cycle. Reservoir pool of phosphorus in ecosystem is the earth’s crust or lithosphere. Weathering of rocks accelerate phosphorus cycle.

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Detritivores )eg. earthworm( break down detritus into smaller particles . This process is called fragmentation. SECTION-B

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Statement A is correct as detritivores do perform fragmentation. Statement B is correct as microbes degrade humus during mineralization. Statement C is correct as water-soluble inorganic nutrients do leach into the soil. Statements D and E are incorrect; the detritus food chain begins with dead organic matter, and earthworms break down detritus through fragmentation, not catabolism. Therefore, option (b) is correct.

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NPP at first trophic level would be the GPP for second trophic level. NPP at second trophic level would be GPP for third trophic level. Therefore, 100 x (kcal/m2/yr) would be GPP at second trophic level and 100x × 10% (kcal/m2/yr) i.e., 10x (kcal/m2/yr) energy would be GPP at third trophic level.

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Statement I is correct as solar energy is the primary source of energy in an ecosystem. Statement II is incorrect because the rate of production of organic matter during photosynthesis is called gross primary productivity (GPP), not net primary productivity (NPP). NPP is GPP minus the energy used by plants for respiration. NCERT XII chapter Ecosystem covers these concepts, so option (c) is correct.

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Statement I is correct as energy flow in ecosystems is unidirectional, moving from producers to consumers. Statement II is incorrect because ecosystems, like all systems, are subject to the second law of thermodynamics, which states that entropy increases in isolated systems. Therefore, option (b) is the most appropriate.

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The rate of biomass production is called productivity. It is expressed in terms of $g{m}^{-2}y{r}^{-1}$ or $(KCal{m}^{-2})y{r}^{-1}$ to compare the productivity of different ecosystems.

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Sun is the only source of energy for all ecosystems on Earth, except for deep sea-hydro-thermal ecosystem.

The energy flow is unidirectional from the sun to producers and then to consumers.

Ecosystems are not exempted from the second law of thermodynamics. They need a constant supply of energy to synthesise the molecules they require to counteract the universal tendency towards increasing disorderliness.