Q.One of the ex situ conservation methods for endangered species is (A) Biosphere reserves (B) National parks (C) Cryopreservation (D) Wildlife sanctuaries
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🔒 Start your 14-day free trial to unlock the full solution →Part (a)Concept understanding — Biodiversity Explanation
Biodiversity: The Web of Life Around You
Imagine walking into a kitchen garden. You see a few tomato plants, some mint, maybe a rose bush. Now imagine walking into a forest — hundreds of tree species, birds calling from every direction, insects crawling under leaves, fungi on the bark, and a stream with tiny fish. That staggering variety of living things — from the tallest tree to the invisible bacteria in the soil — is what we call biodiversity.
The Simple Intuition
Biodiversity is short for biological diversity. Think of it as the "variety of life" on Earth. Just as a library with only one kind of book is boring and limited, an ecosystem with only one kind of plant or animal is fragile and poor. Biodiversity is nature's library — the more species, the richer and more stable the system.
The Precise Meaning
The NCERT textbook defines biodiversity as:
The variety of living organisms present on Earth, including the different plants, animals, fungi, and microorganisms, their genes, and the ecosystems they form.
This definition has three layers, and each matters:
- Genetic diversity — variation within a species. For example, all humans are one species, but we have different eye colours, heights, and resistance to diseases. In crops, genetic diversity means some wheat varieties resist drought while others resist pests.
- Species diversity — the number of different species in a region. A tropical rainforest has thousands of species; a cold desert has very few.
- Ecological diversity — the variety of habitats, ecosystems, and communities. A forest, a grassland, a coral reef, and a pond are all different ecosystems.
Biodiversity is not just about counting species. It includes the genes inside each species and the ecosystems they create together. Lose one layer, and the others suffer.
Why Does Biodiversity Matter?
For a commerce or humanities student, the question is natural: why should I care about how many beetles live in a forest? The answer is that biodiversity is the foundation of everything we use and consume.
Direct economic value — We depend on biodiversity for food (crops, fish, livestock), medicine (many drugs come from plants and fungi), raw materials (timber, cotton, rubber), and tourism (wildlife sanctuaries, national parks).
Indirect value — This is harder to see but more critical. Forests clean the air, wetlands purify water, bees pollinate crops, and soil microbes recycle nutrients. These are called ecosystem services. If biodiversity collapses, these services stop — and no technology can replace them at scale.
Ethical and cultural value — Every species has a right to exist, regardless of its usefulness to humans. Many cultures, especially in India, revere certain trees, animals, and rivers as sacred. Biodiversity is also a source of beauty, inspiration, and knowledge.
The NCERT textbook emphasises that biodiversity is our life insurance. It gives us resilience — when one species fails due to disease or climate change, another can take its place. A system with low biodiversity (like a wheat monoculture) is one disease away from collapse.
A Quick Look at India's Biodiversity
India is one of the world's mega-diverse countries. Though it has only 2.4% of the world's land area, it contains about 8% of all known species. This includes:
- Over 45,000 plant species
- More than 90,000 animal species
- 10 biogeographic zones — from the Himalayas to the Western Ghats to the Andaman Islands
This richness is not accidental. India's varied climate, geography, and ancient landmass have allowed many species to evolve and survive here.
The Threat: Why We Talk About It …
Part (b)Concept understanding — Ecological Concepts
Ecological Concepts: Zooming Out From Organism to Biosphere
Point a camera at a single deer grazing in a forest, and you are looking at an organism. Zoom out a little and you see the whole herd of deer sharing that forest — a population. Zoom out further and the tigers, grasses, insects and fungi living alongside that herd come into frame — a community. Pull back once more and you see the community together with the soil, water, sunlight and air it depends on — an ecosystem. Keep pulling back and entire regions of similar ecosystems (all the world's tropical forests, say) form a biome, and every biome on Earth together makes up the biosphere.
This is the idea of levels of ecological organisation — the same living world, examined at successively larger scales. The NCERT Class XII Biology ecology unit (Chapters 11–13) is built around exactly this zoom-out: Chapter 11 (Organisms and Populations) stays at the organism/population scale, Chapter 12 (Ecosystem) zooms out to the community-plus-environment scale, and Chapter 13 (Biodiversity and Conservation) zooms out again to ask how much variety of life exists and how to protect it. "Ecological Concepts" as a bucket covers facts that sit at any of these scales — not one single narrow idea, but the connected vocabulary ecologists use to describe life at every zoom level.
If a question is specifically about who benefits and who loses when two species interact (mutualism, competition, predation, parasitism, commensalism, amensalism), that is covered in depth in the Ecological Interactions concept. This concept covers the broader structural and functional ideas around it — organisation, ecosystem function, and the systems that move matter and energy through it.
Populations: The First Zoom-Out From the Individual
A population is a group of individuals of the same species living in a defined geographical area at a given time, capable of interbreeding. Because it is a group and not a single organism, a population has properties an individual cannot have on its own — birth rate and death rate (measured per capita, not as raw counts), a sex ratio, an age distribution, and a population density (the size of the population relative to a unit of space). These "group-level" attributes are exactly what distinguishes population ecology from studying one organism's physiology.
Ecosystem Structure: What an Ecosystem Is Made Of
An ecosystem is a functional unit of nature in which living organisms interact with each other and with their physical surroundings. Every ecosystem — a pond, a forest, a crop field, even an aquarium — is built from the same two kinds of components:
- Abiotic components — the non-living inorganic and organic materials: air, water, soil, and the nutrients dissolved in them.
- Biotic components — the living organisms, organised by their functional role: producers (autotrophs that fix solar energy), consumers (heterotrophs that eat producers or each other), and decomposers (fungi and bacteria that break down dead matter).
Two things give an ecosystem its physical shape: its species composition (which plant and animal species are present) and its stratification — the vertical layering of species at different heights, such as tall trees forming the top canopy of a forest, shrubs below them, and grasses and herbs at the ground.
An ecosystem is studied as a working unit through four linked processes: productivity, decomposition, energy flow, and nutrient cycling. Every "how does an ecosystem function" question is really asking about one of these four.
Productivity: How Fast an Ecosystem Makes New Matter
Primary productivity is the rate at which producers capture solar energy and convert it into organic (biomass) matter.
- Gross Primary Productivity (GPP) — the total rate of production of organic matter, i.e. the total solar energy fixed by all producers.
- Net Primary Productivity (NPP) — what is left of GPP after the producers themselves use some of it up in their own respiration: NPP = GPP − Respiration losses (R). NPP is the biomass actually available to the consumers (herbivores and decomposers) of the ecosystem.
- Secondary productivity is the rate at which consumers assimilate the food energy they take in from producers or from other consumers.
Decomposition: Breaking Matter Back Down
Decomposers convert the complex organic compounds in dead plant and animal remains ("detritus") back into simple inorganic nutrients, so those nutrients can be reused by producers. This happens in three overlapping steps:
- Fragmentation — detritivores (like earthworms) physically break detritus into smaller particles.
- Leaching — water-soluble inorganic nutrients seep down through the soil and are lost from the topsoil layer as precipitates.
- Catabolism — bacterial and fungal enzymes chemically break down the remaining detritus into simpler inorganic substances.
Partial decomposition leaves behind a dark, colloidal, highly microbe-resistant substance called humus, which acts as a slow-release nutrient reservoir; its further breakdown to release inorganic nutrients is called mineralisation. Decomposition is largely an oxygen-requiring process, is slower when detritus is rich in lignin/chitin, and is faster when it is rich in nitrogen and simple sugars — warm, moist conditions favour it, while cold and waterlogged (anaerobic) conditions suppress it and let organic matter accumulate.
Energy Flow and Ecological Pyramids
Unlike nutrients, energy in an ecosystem flows in one direction only — from the sun, into producers, and then into successive consumers — and is progressively lost as heat at every transfer; it is never recycled back to the producers the way a nutrient is. Because a real ecosystem rarely has a single, unbranched sequence of "who eats whom," feeding relationships form an interconnected food web rather than one isolated food chain.
Ecological pyramids represent this trophic structure visually (producers at the base, successive consumers stacked above):
A pyramid of energy is always upright — it can never be inverted, because energy is always lost as heat at each transfer, so a lower trophic level must always contain more energy than the level above it. Pyramids of numbers and biomass can be inverted in some ecosystems — the classic example is a marine ecosystem, where the biomass of fish (consumers) can exceed the biomass of the phytoplankton (producers) that support them, because the phytoplankton reproduce and get eaten so fast.
Nutrient (Biogeochemical) Cycling …
Part (a)
Biosphere reserves, national parks and wildlife sanctuaries protect species in their natural habitat, so they are in situ methods. Cryopreservation - storing gametes, seeds or tissues at very low temperature (e.g. in liquid nitrogen) outside the natural habitat - is an ex situ conservation method. …
Part (a): The ex situ conservation method among the options is CRYOPRESERVATION - option (C). Part (b): Stratospheric ozone is continuously formed by the action of UV rays on molecular oxygen - option (C).
Part (a)
In situ conservation protects organisms in their natural habitat - this includes biosphere reserves, national parks and wildlife sanctuaries. Ex situ conservation protects them outside their natural habitat, e.g. zoos, botanical gardens, seed banks and cryopreservation (storing gametes, seeds, tissues or embryos at very low temperature, such as in liquid nitrogen at -196 C). Of the options, only cryopreservation is ex situ. …
Showing the 12 most recent of 64 on this concept.
- CBSE 2026Set 57/1/11 markMCQQ.In an ecosystem, different species occupy different levels and vertical distribution of species is found. This is called _________. (A) Stratification (B) Layering (C) Fragmentation (D) Population
›Reveal solutionSolution
The vertical distribution of different species across distinct height levels in an ecosystem is called stratification.
When you walk into a forest, you're not looking at a flat carpet of life—you're seeing a three-dimensional structure where different organisms live at different heights, each layer buzzing with its own community. This vertical arrangement is one of the most elegant organizing principles in ecology.
Think of a tropical rainforest. The tallest trees form an emergent layer, their crowns breaking through to full sunlight. Below them spreads the main canopy, a dense roof where most of the forest's photosynthesis happens and countless birds, insects, and epiphytes make their home. Beneath that lies the understory, a shadier zone of smaller trees and saplings adapted to low light. Closer to the ground, shrubs and herbs form another layer, and finally the forest floor itself—dark, humid, rich with decomposers breaking down leaf litter.
Each of these layers represents a different microhabitat with its own temperature, humidity, and light conditions. A canopy-dwelling monkey and a ground-dwelling porcupine might live in the same forest, but they occupy entirely different vertical zones—different strata. This isn't random; it's the result of species evolving to exploit specific niches at specific heights, reducing competition and allowing more species to coexist in the same horizontal space.
NoteStratification isn't limited to forests. Aquatic ecosystems show it too—think of the sunlit surface zone, the twilight middle depths, and the dark ocean floor, each supporting different communities adapted to pressure, light, and temperature at that depth. …
- CBSE 2026Set 57/3/11 markMCQQ.Which of the following is not a functional unit of an ecosystem ? (A) Energy flow (B) Decomposition (C) Stratification (D) Productivity
›Reveal solutionSolution
Stratification is a structural characteristic of an ecosystem, not a functional unit. The key functional units are productivity, decomposition, energy flow, and nutrient cycling.
An ecosystem is a fascinating and complex system where living organisms interact with each other and with their non-living environment. Think of a forest, a pond, or even a small patch of garden – each is an ecosystem, a self-sustaining unit. To truly understand how these systems operate, we look at their fundamental processes, often referred to as their functional units. These are the dynamic activities that keep the ecosystem alive and thriving.
The core functional units of any ecosystem are the processes that govern the flow of energy and the cycling of nutrients. These processes ensure the continuous existence and health of the biotic community within its abiotic surroundings. Let's explore the primary functional units:
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Productivity: This refers to the rate at which biomass is produced in an ecosystem. It's essentially how much organic matter is generated.
- Primary productivity is the rate at which producers (like plants) convert solar energy into organic compounds through photosynthesis. It's the foundation of almost all ecosystems.
- Secondary productivity is the rate at which consumers (herbivores, carnivores) assimilate energy and form new organic matter from the food they eat.
ImportantProductivity is a measure of the ecosystem's capacity to generate organic material, which forms the basis of the food web.
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Decomposition: This is the vital process by which decomposers, primarily bacteria and fungi, break down dead organic matter (detritus) into simpler inorganic substances. This process is crucial because it recycles nutrients back into the soil or water, making them available for producers once again. Without decomposition, nutrients would be locked up in dead organisms, and life would eventually cease.
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Energy Flow: Energy is the driving force of an ecosystem. It flows unidirectionally, meaning it moves from the sun to producers, then to various levels of consumers, and finally to decomposers. Energy is captured by producers, transferred through different trophic levels (feeding levels), and a significant portion is lost as heat at each transfer. This continuous flow ensures that all organisms receive the energy they need to survive. …
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- CBSE 2026Set A1 markMCQQ.How many mega-biodiversity countries are there in the world?(a) 25(b) 34(c) 14(d) 17
›Reveal solutionSolution
The world has 17 megadiverse countries that together hold most of the Earth's species; India is one of them.
A small number of countries lying largely within the tropics harbour a very large share of the world's biodiversity. These are termed megadiverse (mega-biodiversity) countries and number 17, including …
- CBSE 2026Set A1 markMCQQ.Which region got comparatively shorter span of time for species evolution and diversification due to frequent glaciation?(a) temperate region(b) tropical region(c) polar region(d) glaciation occurred in all regions
›Reveal solutionSolution
Tropics stayed relatively undisturbed and had more evolutionary time; temperate regions faced frequent glaciations, giving less time for diversification.
One explanation for the greater species richness of the tropics is time: tropical latitudes have remained relatively undisturbed for millions of years, providing a long, stable period for species to evolve and diversify. Temperate regions, in contrast, were subj …
- CBSE 2026Set ANNUAL1 markMCQQ.Which of the following is not a functional unit of the ecosystem?(a) Energy flow(b) Decomposition(c) Stratification(d) Productivity
›Reveal solutionSolution
Unlike energy flow, decomposition, and productivity, which are dynamic functional processes of an ecosystem, stratification is a structural feature describing vertical layering of organisms.
The functional aspects (functional units) of an ecosystem are generally described as: productivity (the rate of biomass generation), decomposition (breakdown of dead organic matter), energy flow (the unidirectional movement of energy from sun through trophic levels), and nutrient cycling. Stratification, in contrast, refers to the vertical layering/organisation of different species within a community (e.g., canopy, shrub, and herb layers in a f …
- CBSE 2026Set ANNUAL1 markQ.Fill in the blank: When a species become extinct, the plant and animal species associated with an obligatory way also become extinct. It is called ______.
›Reveal solutionSolution
The linked extinction of dependent species along with the species they rely on is called co-extinction.
Many species are so closely dependent on another species (for food, host or partner) that they cannot survive without it. When such a host or partner species becomes extinct, the plants and animals that were obligately associated with it also die out. This linked loss is called co-extinction, for exa …
- CBSE 2026Set ANNUAL1 markMCQQ.The possible reason for extinction of Steller's sea cow is due to –(a) Alien species invasion(b) Over exploitation(c) Habitat Loss(d) Co-extinction
›Reveal solutionSolution
Steller's sea cow became extinct because humans hunted it excessively — an example of over-exploitation.
Over-exploitation is one of the major causes of biodiversity loss ("The Evil Quartet"): when a resource is harvested by humans faster than it can replenish, the species declines to extinction. Steller's sea cow (Hydrodamalis gigas) was a large, docile marine mammal that was kill …
- CBSE 2025Set F1 markMCQQ.Which of the following is a biotic component of ecosystem?(a) Air(b) Sunlight(c) Water(d) Producer
›Reveal solutionSolution
Producers are the biotic (living) component; air, sunlight and water are abiotic.
An ecosystem has two kinds of components. Abiotic (non-living) components include physical and chemical factors such as air, sunlight, water, temperature and soil minerals. Biotic (living) components include producers (green plants/autotrophs), consumers (herbiv …
- CBSE 2025Set F1 markMCQQ.Where are woody lianas / climbers found?(a) Taiga(b) Deciduous forest(c) Tropical rain forest(d) Shrub (chaparral)
›Reveal solutionSolution
Woody lianas (large climbers) are typical of tropical rain forests.
Lianas are thick, woody climbing plants that root in the ground but use tall trees to reach sunlight in the canopy. They flourish in the warm, humid, densely vegetated tropical rain forest, which has the highest biodiversity and vertical stratification of any biome. Taiga (coniferous), temperate deciduous fore …
- CBSE 2025Set F1 markMCQQ.Which of the following terms is used for the population found in a particular area?(a) Natural(b) Endemic(c) Alien(d) Pandemic
›Reveal solutionSolution
Species/populations confined to a particular area are termed endemic.
Endemic refers to a species or population whose natural occurrence is restricted to one particular geographic area and is found nowhere else (for example, many species endemic to the Western Ghats). "Alien" species, by contrast, are introduced from outside a region, and "pandemic" refers …
- CBSE 2025Set ZOOLOGY1 markMCQQ.Which term is used for the conservation of biodiversity outside the natural habitat?(i) In vivo(ii) Ex situ(iii) In situ(iv) In vitro
›Reveal solutionSolution
Ex situ conservation protects biodiversity outside the natural habitat (zoos, botanical gardens, seed/gene banks, etc.).
Conservation strategies are of two main types:
- In situ conservation — protecting species within their natural habitat (national parks, sanctuaries, biosphere reserves).
- Ex situ conservation — protecting species outside their natural habitat, e.g. zoological parks, botanical gardens, wildlife safari parks, seed banks, gene banks, cryopreservation and tissue culture. …
- CBSE 2024Set E1 markMCQQ.Biodiversity of India is what percentage of the total global species diversity?(a) 2.4%(b) 8.1%(c) 5%(d) 9%
›Reveal solutionSolution
India holds 8.1% of global species diversity on just 2.4% of the world's land area — making it a megadiversity country.
Despite occupying only about 2.4% of the world's land area, India accounts for 8.1% of the total global species diversity. This makes India one of the 17 mega-diverse countries of the world. The contrast between th …
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