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Step-by-step answers for all textbook questions in this chapter
The Biosphere — Exercise Solutions
How to Use This Page
Welcome to the Samacheer Kalvi Class 11 Geography solutions for The Biosphere chapter. This page covers every exercise question with detailed answers, concept recaps, and exam tips.
Quick navigation:
- Jump to [Key Concepts](#key-concepts-quick-recap) for a rapid revision of theory
- Head to [MCQs](#i-choose-the-best-answer-mcqs) if you want to practise objective questions
- Use [Answer in Detail](#vi-answer-in-detail) for long-answer preparation
- Check the [Exam Checklist](#exam-checklist) before your exam
Tip: Read the concept recap first, then attempt each section on your own before reading the answer. Active recall strengthens memory far more than passive reading.
Key Concepts (Quick Recap)
Biosphere — Definition, Extent, Significance
The biosphere is the narrow zone of Earth where living organisms exist. It extends roughly from 5 km below sea level (deep ocean trenches) to 8 km above sea level (upper atmosphere). It overlaps parts of the lithosphere, hydrosphere, and atmosphere.
Key points:
- The term "biosphere" was coined by Eduard Suess (1875).
- The concept was elaborated by Vladimir Vernadsky, who described the biosphere as the sphere of living matter.
- The biosphere is not uniformly distributed — life is concentrated in zones where conditions (temperature, water, light) are favourable.
- It is an open system — energy enters from the Sun and matter is exchanged with other spheres.
Significance:
1. Supports all life forms on Earth 2. Drives biogeochemical cycles (carbon, nitrogen, oxygen, water) 3. Maintains the composition of the atmosphere (oxygen by photosynthesis, CO₂ regulation) 4. Provides resources — food, fibre, fuel, medicine
Ecosystem — Definition and Components
An ecosystem is a functional unit of nature where living organisms interact with each other and with the physical environment. The term was introduced by A.G. Tansley (1935).
Biotic Components:
| Component | Role | Examples |
|---|---|---|
| Producers (Autotrophs) | Convert solar energy into chemical energy via photosynthesis | Green plants, algae, cyanobacteria |
| Consumers (Heterotrophs) | Depend on producers or other consumers for food | Herbivores (deer, rabbit), Carnivores (lion, hawk), Omnivores (bear, human) |
| Decomposers (Saprotrophs) | Break down dead organic matter, recycle nutrients | Bacteria, fungi, earthworms |
Types of Consumers:
- Primary consumers (Herbivores): Feed directly on producers — grasshopper, deer
- Secondary consumers (Carnivores): Feed on herbivores — frog, small fish
- Tertiary consumers (Top carnivores): Feed on secondary consumers — eagle, tiger
- Omnivores: Feed on both plants and animals — bear, human
Abiotic Components:
- Climatic factors: Temperature, humidity, sunlight, wind, precipitation
- Edaphic factors: Soil type, pH, minerals, texture
- Chemical factors: Oxygen, carbon dioxide, nitrogen, phosphorus
- Physical medium: Water (aquatic), air and land (terrestrial)
Food Chain, Food Web, Trophic Levels, and Energy Flow
Food Chain: A linear sequence showing energy transfer from producers to top carnivores.
Food Web: A network of interconnected food chains showing multiple feeding relationships within an ecosystem. It provides ecological stability — if one food source declines, consumers can switch to alternatives.
Trophic Levels:
| Trophic Level | Organism Type | Example |
|---|---|---|
| T1 (First) | Producers | Grass, phytoplankton |
| T2 (Second) | Primary consumers | Grasshopper, zooplankton |
| T3 (Third) | Secondary consumers | Frog, small fish |
| T4 (Fourth) | Tertiary consumers | Snake, large fish |
| T5 (Fifth) | Quaternary / Apex | Eagle, shark |
10% Law of Energy Flow (Lindeman, 1942):
- Only about 10% of energy is transferred from one trophic level to the next.
- The remaining 90% is lost as heat (respiration, metabolism, excretion).
- This limits the number of trophic levels in a food chain (usually 3–5).
Ecological Pyramids
Ecological pyramids are graphical representations of trophic structure.
| Pyramid Type | Basis | Shape | Notes |
|---|---|---|---|
| Pyramid of Numbers | Number of organisms at each level | Usually upright (exceptions: parasitic food chain — inverted) | A single tree supports many herbivores, which support more parasites |
| Pyramid of Biomass | Total biomass at each level | Upright in terrestrial; inverted in aquatic (phytoplankton have less standing biomass but high turnover) | Biomass = number x average weight |
| Pyramid of Energy | Energy at each level per unit time | Always upright | Most fundamental; energy always decreases at higher levels |
Biomes — Major World Biomes
A biome is a large geographical area of distinctive plant and animal groups adapted to a particular climate. Biomes are classified primarily by temperature and precipitation.
| Biome | Climate | Vegetation | Fauna | Location |
|---|---|---|---|---|
| Tropical Rainforest | Hot and wet (25–28 °C, 200 cm+/yr) | Multi-layered canopy, broadleaf evergreen | Jaguar, toucan, orangutan, gorilla | Amazon, Congo, Southeast Asia |
| Savannah | Warm, seasonal rainfall (100–150 cm/yr) | Tall grasses, scattered trees (acacia) | Lion, zebra, giraffe, elephant | East Africa, Brazilian Cerrado |
| Desert | Hot day, cold night, <25 cm/yr rain | Xerophytes (cactus, succulents), sparse | Camel, lizard, snake, scorpion | Sahara, Thar, Arabian, Atacama |
| Mediterranean | Warm dry summer, mild wet winter | Sclerophyllous shrubs, olive, cork | Goat, sheep, lynx | Mediterranean coast, California, Chile |
| Temperate Grassland | Moderate rainfall (25–75 cm/yr) | Grasses, few trees | Bison, antelope, prairie dog | Prairies (N. America), Pampas (S. America), Steppes (Asia) |
| Taiga (Coniferous Forest) | Cold, moderate snow (30–60 cm/yr) | Conifers (spruce, fir, pine) | Moose, wolf, bear, beaver | Canada, Scandinavia, Siberia |
| Tundra | Extremely cold, <25 cm/yr | Mosses, lichens, dwarf shrubs | Reindeer, arctic fox, polar bear | Arctic regions, high mountains |
| Monsoon Forest | Seasonal rainfall (100–200 cm/yr), distinct wet-dry | Deciduous trees (teak, sal, sandalwood) | Tiger, deer, peacock, monkey | India, Myanmar, Thailand |
Biodiversity — Definition, Types, Importance
Biodiversity refers to the variety of life forms at all levels — from genes to ecosystems. The term was popularised by Walter G. Rosen (1985) and the concept elaborated by E.O. Wilson.
Types of Biodiversity:
| Type | Description | Example |
|---|---|---|
| Genetic diversity | Variation in genes within a species | Different rice varieties in India (over 50,000 landraces) |
| Species diversity | Number of species in a given area | Western Ghats — 500+ bird species |
| Ecosystem diversity | Variety of habitats, ecological processes | Wetlands, forests, grasslands, coral reefs |
Importance of Biodiversity:
1. Ecological stability: Species-rich ecosystems are more resilient to disturbance 2. Economic value: Food, timber, fibre, medicine — 25% of pharmaceuticals derived from plants 3. Scientific value: Genetic resources for biotechnology, crop improvement 4. Ethical value: Every species has an intrinsic right to exist 5. Aesthetic and cultural value: Tourism, spiritual significance, inspiration 6. Ecosystem services: Pollination, nutrient cycling, water purification, climate regulation
Ecological Balance and Succession
Ecological balance is a state of dynamic equilibrium in an ecosystem where species populations and environmental factors remain relatively stable over time.
Ecological Succession: The gradual and predictable process of change in species structure of an ecosystem over time.
| Type | Starting Condition | Example |
|---|---|---|
| Primary succession | Bare, lifeless surface (no soil) | Lichens and mosses colonising bare rock → soil formation → grasses → shrubs → trees |
| Secondary succession | Disturbed area with soil already present | Regrowth after forest fire, abandoned farmland |
Stages in Primary Succession (Xerosere):
1. Pioneer stage — Crustose lichens on bare rock 2. Foliose lichen stage — Weathering of rock begins 3. Moss stage — Soil starts forming 4. Herb stage — Grasses and herbs colonise 5. Shrub stage — Woody shrubs dominate 6. Forest stage (Climax) — Stable, self-perpetuating community
Human Impact on the Biosphere
| Impact | Description | Consequence |
|---|---|---|
| Deforestation | Clearing forests for agriculture, urbanisation | Habitat loss, soil erosion, carbon release, disrupted water cycle |
| Pollution | Air (CO₂, SO₂), water (sewage, chemicals), soil (pesticides, heavy metals) | Acid rain, eutrophication, bioaccumulation, health hazards |
| Climate change | Greenhouse gas emissions raising global temperatures | Sea level rise, extreme weather, species migration, coral bleaching |
| Overexploitation | Overfishing, overgrazing, excessive mining | Species depletion, resource exhaustion, habitat degradation |
| Urbanisation | Expansion of cities and infrastructure | Loss of agricultural land, heat islands, fragmentation of habitats |
| Invasive species | Introduction of non-native species | Displacement of native species, ecological imbalance |
Conservation — Biosphere Reserves, National Parks, Wildlife Sanctuaries
Conservation strategies in India:
| Category | Purpose | Human Activity | Examples |
|---|---|---|---|
| Biosphere Reserve | Conservation of biodiversity, research, sustainable development | Limited in buffer zone; core zone is strictly protected | Nilgiri, Nanda Devi, Sunderbans |
| National Park | Protection of wildlife and habitat | No human settlement or resource use | Bandipur, Kanha, Gir |
| Wildlife Sanctuary | Protection of specific species | Limited human activity permitted | Mudumalai, Vedanthangal |
Biosphere Reserves in India (UNESCO-recognised):
| No. | Biosphere Reserve | State | Key Feature |
|---|---|---|---|
| 1 | Nilgiri | Tamil Nadu, Kerala, Karnataka | First biosphere reserve; Western Ghats biodiversity |
| 2 | Nanda Devi | Uttarakhand | High-altitude Himalayan ecosystem |
| 3 | Sunderbans | West Bengal | Largest mangrove forest; Royal Bengal Tiger |
| 4 | Gulf of Mannar | Tamil Nadu | Marine biosphere; coral reefs, dugong |
| 5 | Great Nicobar | Andaman and Nicobar | Tropical rainforest, indigenous tribes |
| 6 | Similipal | Odisha | Mixed deciduous forest, tiger reserve |
| 7 | Manas | Assam | Grassland and forest; Golden Langur |
| 8 | Khangchendzonga | Sikkim | Himalayan and trans-Himalayan ecosystems |
| 9 | Panna | Madhya Pradesh | Dry deciduous forest, tiger reintroduction |
| 10 | Achanakmar-Amarkantak | Chhattisgarh, Madhya Pradesh | Tropical deciduous forest, catchment area |
I. Choose the Best Answer (MCQs)
Suess introduced the term "biosphere" in 1875. Vernadsky later expanded the concept into a full scientific framework.
Lindeman (1942) demonstrated that only about 10% of energy is transferred from one trophic level to the next, with the rest lost as heat.
The pyramid of energy is always upright because energy always decreases at each successive trophic level. Pyramids of numbers and biomass can be inverted in certain ecosystems.
The tundra biome has permanently frozen subsoil (permafrost), extremely low temperatures, and vegetation dominated by mosses, lichens, and dwarf shrubs.
In a parasitic food chain (e.g., tree → herbivore → parasite → hyperparasite), a single tree supports many herbivores, which support even more parasites, producing an inverted pyramid of numbers.
The Nilgiri Biosphere Reserve, established in 1986, was the first in India. It spans Tamil Nadu, Kerala, and Karnataka.
Primary succession starts on a lifeless surface without soil (e.g., newly formed volcanic rock). Secondary succession begins in areas where soil already exists (options a, b, d).
II. Fill in the Blanks
1. The zone of Earth where life exists is called the biosphere.
2. The term "ecosystem" was introduced by A.G. Tansley in 1935.
3. Organisms that produce their own food through photosynthesis are called producers or autotrophs.
4. In a food chain, energy flows from producers to consumers.
5. According to the 10% law, only 10 percent of energy is transferred from one trophic level to the next.
6. The pyramid of energy is always upright.
7. Decomposers break down dead organic matter and recycle nutrients back into the ecosystem.
8. The tundra biome is characterised by permafrost.
9. The variety of life at all levels — genetic, species, and ecosystem — is called biodiversity.
10. Primary succession occurs on a bare, lifeless surface without any soil.
11. The Nilgiri Biosphere Reserve was the first to be established in India.
12. The Sunderbans Biosphere Reserve is known for the Royal Bengal Tiger and mangrove forests.
III. True or False
IV. Match the Following
| Column A | Column B |
|---|---|
| 1. Biosphere | (c) Zone of life on Earth |
| 2. Producers | (e) Autotrophs that perform photosynthesis |
| 3. Taiga | (a) Coniferous forest biome |
| 4. Parasitic food chain | (f) Inverted pyramid of numbers |
| 5. Gulf of Mannar | (d) Marine biosphere reserve |
| 6. Secondary succession | (b) Occurs in disturbed areas with soil present |
Matched pairs:
| 1 → c | 2 → e | 3 → a | 4 → f | 5 → d | 6 → b |
|---|
V. Answer Briefly
1. Define biosphere and mention its extent.
The biosphere is the part of Earth where living organisms exist. It extends from about 5 km below sea level (deep ocean trenches) to about 8 km above sea level (troposphere). It overlaps parts of the lithosphere (rock and soil), hydrosphere (water bodies), and atmosphere (air). It is the global ecological system integrating all living beings and their relationships.
2. What is a food web? How does it differ from a food chain?
A food web is a network of interconnected food chains showing the complex feeding relationships within an ecosystem. While a food chain shows a single linear path of energy flow (e.g., Grass → Deer → Tiger), a food web shows multiple paths and alternative food sources for each organism.
Key differences:
| Feature | Food Chain | Food Web |
|---|---|---|
| Structure | Linear, single path | Complex, network |
| Stability | Less stable | More stable |
| Feeding options | One food source per level | Multiple food sources |
| Ecological significance | Simplistic model | Realistic representation |
A food web provides greater ecological stability because if one food source declines, organisms can switch to alternatives.
3. List any four biosphere reserves in India.
The four biosphere reserves in India are:
1. Nilgiri — Tamil Nadu, Kerala, Karnataka (first biosphere reserve of India, 1986) 2. Nanda Devi — Uttarakhand (Himalayan high-altitude ecosystem) 3. Sunderbans — West Bengal (largest mangrove forest, Royal Bengal Tiger) 4. Gulf of Mannar — Tamil Nadu (marine biosphere, coral reefs, dugong)
Other notable reserves include Great Nicobar, Similipal, Manas, and Khangchendzonga.
4. What is the 10% law of energy transfer?
The 10% law, proposed by Raymond Lindeman (1942), states that only about 10% of the energy available at one trophic level is transferred to the next trophic level. The remaining 90% is used for metabolic processes (respiration, movement, digestion) or lost as heat.
Example:
- Producers (grass) — 10,000 kJ
- Primary consumers (grasshopper) — 1,000 kJ
- Secondary consumers (frog) — 100 kJ
- Tertiary consumers (snake) — 10 kJ
This explains why food chains rarely exceed 4–5 trophic levels — there is simply not enough energy left to sustain higher levels.
VI. Answer in Detail
1. Explain the concept of ecosystem with its components and functioning.
An ecosystem is a functional unit of nature where living organisms interact with each other and with their physical environment. The concept was introduced by A.G. Tansley in 1935. An ecosystem can be as small as a pond or as large as a forest.
Types of Ecosystems:
| Type | Examples |
|---|---|
| Natural | Forest, grassland, desert, ocean, river |
| Artificial | Cropland, garden, aquarium, park |
| Terrestrial | Forest, grassland, desert |
| Aquatic | Freshwater (pond, lake, river), Marine (ocean, estuary) |
Components of an Ecosystem:
A. Biotic Components (Living):
1. Producers (Autotrophs): Green plants, algae, and cyanobacteria that synthesise organic food from inorganic substances using solar energy through photosynthesis. They form the base of all food chains.
2. Consumers (Heterotrophs): Organisms that cannot produce their own food and depend on producers or other consumers.
- Primary consumers (Herbivores): Grasshopper, deer, rabbit — feed on producers
- Secondary consumers (Carnivores): Frog, snake — feed on herbivores
- Tertiary consumers (Top carnivores): Eagle, lion — feed on secondary consumers
- Omnivores: Bear, human — feed on both plants and animals
3. Decomposers (Saprotrophs): Bacteria, fungi, and earthworms that decompose dead organic matter. They recycle nutrients back into the soil and atmosphere, making them available to producers again. Without decomposers, nutrient cycling would stop.
B. Abiotic Components (Non-living):
1. Climatic factors: Temperature, sunlight, humidity, wind, rainfall 2. Edaphic factors: Soil type, pH, mineral content, texture, topography 3. Chemical factors: Oxygen, carbon dioxide, nitrogen, phosphorus, sulphur 4. Physical medium: Water (aquatic ecosystems), air and land (terrestrial ecosystems)
Functioning of an Ecosystem:
Ecosystems function through three key processes:
1. Energy Flow: Energy enters from the Sun, is captured by producers through photosynthesis, and flows through the food chain from producers to consumers to decomposers. Energy flow is unidirectional — it does not cycle back. The 10% law governs energy transfer between trophic levels.
2. Nutrient Cycling (Biogeochemical Cycles): Unlike energy, nutrients (carbon, nitrogen, oxygen, phosphorus, water) are recycled between biotic and abiotic components. Decomposers play a vital role in returning nutrients to the soil and atmosphere.
3. Ecological Succession: Ecosystems change over time through a predictable sequence of species replacements, eventually reaching a stable climax community.
Summary diagram of ecosystem functioning:
Thus, an ecosystem is a self-sustaining, self-regulating unit where energy flows unidirectionally and nutrients cycle continuously.
2. Describe the major biomes of the world with their characteristics.
A biome is a large geographical region with a specific climate, soil type, vegetation, and animal life. Biomes are primarily determined by temperature and precipitation patterns. The major biomes of the world are described below:
3. Discuss the importance of biodiversity and the impact of human activities on the biosphere.
Importance of Biodiversity:
Biodiversity — the variety of life at genetic, species, and ecosystem levels — is essential for the functioning and stability of the biosphere. Its importance can be discussed under the following heads:
Impact of Human Activities on the Biosphere:
Human activities have profoundly altered the biosphere, leading to what many scientists call the sixth mass extinction. The major impacts are:
Common Mistakes to Avoid
1. Confusing biosphere with ecosystem: The biosphere is the global zone of life (the entire planetary system), while an ecosystem is a local functional unit (a pond, a forest, a desert). Every ecosystem is part of the biosphere, but not vice versa.
2. Saying the pyramid of biomass is always upright: This is true for terrestrial ecosystems but false for aquatic ecosystems, where phytoplankton (producers) have very low standing biomass compared to zooplankton and fish, resulting in an inverted pyramid.
3. Confusing primary and secondary succession: Primary succession begins on a bare, lifeless surface with no soil (e.g., volcanic rock, glacial moraine). Secondary succession begins where soil already exists (e.g., after a forest fire, abandoned farmland). The key difference is the presence or absence of soil.
4. Confusing food chain and food web: A food chain is a single linear path of energy transfer. A food web is a complex network of interconnected food chains. Always use food webs for realistic ecosystem descriptions.
5. Assuming all deserts are hot: Cold deserts exist too — the Gobi Desert in Mongolia and the Ladakh region in India are cold deserts with winter temperatures well below freezing.
6. Confusing biosphere reserves with national parks: Biosphere reserves have three zones (core, buffer, transition) and allow limited human activity in the buffer and transition zones. National parks are strictly protected with no human settlement or resource extraction. Wildlife sanctuaries protect specific species and may allow limited human activity.
7. Thinking decomposers are at the top of the food chain: Decomposers operate across all trophic levels, breaking down dead matter from producers, consumers, and other decomposers. They are not a single trophic level but are essential for nutrient cycling.
8. Forgetting the 10% law in energy calculations: When asked to calculate energy at a trophic level, always apply the 10% rule. If producers have 10,000 kJ, primary consumers get 1,000 kJ, secondary consumers get 100 kJ, and so on. Do not forget that 90% is lost as heat at each transfer.
Exam Checklist
Before your exam, make sure you can answer YES to each of these:
- [ ] Can I define the biosphere and state its extent (5 km below to 8 km above sea level)?
- [ ] Can I list and explain the biotic and abiotic components of an ecosystem?
- [ ] Can I draw and explain a food chain and a food web with examples?
- [ ] Can I state the 10% law of energy transfer and apply it to calculate energy at different trophic levels?
- [ ] Can I describe all three types of ecological pyramids and explain when each is upright or inverted?
- [ ] Can I name at least 6 major biomes and describe their climate, vegetation, and fauna?
- [ ] Can I define biodiversity and distinguish between genetic, species, and ecosystem diversity?
- [ ] Can I explain the difference between primary and secondary succession with examples?
- [ ] Can I list at least 5 biosphere reserves in India with their states and key features?
- [ ] Can I discuss at least 4 human impacts on the biosphere and corresponding conservation measures?
For more Class 11 Geography resources, see our guides on [Hydrosphere](/class/11/geography/solutions/hydrosphere-exercise-solutions) and [Atmosphere](/class/11/geography/solutions/atmosphere-exercise-solutions).