Samacheer Kalvi 9th Social Science Biosphere Exercise Solutions | KalviGavani

Biosphere — Exercise Solutions Guide

Solve every exercise on your own first, then cross-check your answers here. Understanding why an answer is correct matters more than memorising it.

I. Multiple Choice Questions (MCQs)

**Q1. The biosphere is the zone where the lithosphere, hydrosphere, and ___ interact.

(a) Stratosphere (b) Atmosphere (c) Mesosphere (d) Exosphere

**Q2. An organism that makes its own food using sunlight is called a

(a) Heterotroph (b) Decomposer (c) Autotroph (d) Parasite

**Q3. The tropical rainforest biome is characterised by

(a) Low rainfall and high temperature (b) High rainfall and high temperature throughout the year (c) Low rainfall and low temperature (d) Moderate rainfall and low temperature

**Q4. In an ecological pyramid, the number of organisms at the producer level is

(a) Smallest (b) Equal to primary consumers (c) Largest (d) Same as top carnivores

**Q5. Which biome is known as the "breadbasket of the world"?

(a) Tropical rainforest (b) Taiga (c) Tundra (d) Steppe/Grassland

**Q6. The transfer of energy from producers to top carnivores is called a

(a) Food web (b) Nutrient cycle (c) Food chain (d) Ecological succession

**Q7. The taiga biome is dominated by

(a) Broad-leaved deciduous trees (b) Coniferous trees (c) Cacti and shrubs (d) Grasses and herbs

**Q8. Which of the following is an abiotic component of an ecosystem?

(a) Plants (b) Bacteria (c) Sunlight (d) Animals

**Q9. The gradual process of change in an ecosystem over time is called

(a) Food chain (b) Ecological succession (c) Food web (d) Ecological pyramid

**Q10. An organism that feeds on dead and decaying matter is called a

(a) Producer (b) Consumer (c) Decomposer (d) Autotroph

**Q11. The tundra biome is found in

(a) Near the equator (b) Mid-latitudes (c) Near the poles and high mountains (d) Coastal areas

**Q12. The maximum energy in an ecosystem flows through

(a) Producers (b) Primary consumers (c) Secondary consumers (d) Top carnivores

II. True or False

1. The biosphere includes only living organisms.

2. In a food chain, energy decreases at each trophic level.

3. Desert biomes receive very little rainfall and have extreme temperatures.

4. Decomposers are also called autotrophs.

5. The savanna biome has distinct wet and dry seasons.

6. A food web is a single linear chain of organisms.

7. Biodiversity is greatest in the tropical rainforest biome.

8. Producers occupy the first trophic level in an ecological pyramid.

9. The Mediterranean biome is characterised by hot, dry summers and mild, wet winters.

10. Ecological pyramids are always upright.

III. Fill in the Blanks

1. The part of the Earth where life exists is called the ___.

2. Organisms that produce their own food are called ___.

3. The non-living components of an ecosystem are called ___ factors.

4. The largest biome on Earth is the ___.

5. The sequence of organisms through which energy flows in an ecosystem is called a ___.

6. Organisms that break down dead and decaying matter are called ___.

7. The biome with permanently frozen subsoil is called the ___.

8. The tropical grassland with scattered trees is called the ___.

9. The variety of life in all its forms is called ___.

10. The gradual change in ecosystem composition over time is called ecological ___.

IV. Match the Following

1 → d — Tropical rainforests are found near the equator and have the highest biodiversity of any biome. They are dominated by tall, broad-leaved evergreen trees forming a dense canopy, with abundant epiphytes, vines, and understory plants. Annual rainfall exceeds 200 cm and temperatures remain warm year-round.

2 → c — The taiga (boreal forest) biome is dominated by coniferous trees (spruce, fir, pine) that are adapted to long, cold winters and short summers. It stretches across northern North America, Europe, and Asia, forming the largest terrestrial biome.

3 → b — The tundra biome is found near the poles and at high mountain altitudes. It is characterised by permafrost (permanently frozen subsoil), extremely cold temperatures, short growing seasons, and low-growing vegetation including lichens, mosses, dwarf shrubs, and grasses.

4 → e — Deserts are characterised by sparse vegetation (cacti, xerophytes, thorny shrubs) adapted to extreme temperatures (hot days, cold nights) and very low rainfall (less than 25 cm per year). Animals have adaptations like nocturnal behaviour and water conservation.

5 → a — The Mediterranean biome (chaparral) has hot, dry summers and mild, wet winters. Vegetation includes drought-resistant shrubs, sclerophyllous (hard-leaved) plants, olive trees, and cork oak. Found around the Mediterranean Sea, in California, central Chile, and parts of Australia.

V. Short Answer Questions (2-3 marks)

Q1. What is an ecosystem? Name its two main components.

An ecosystem is a self-contained unit consisting of all the living organisms (biotic community) and the non-living environment (abiotic factors) in a specific area, interacting with each other through energy flow and nutrient cycling. The two main components are: (1) Biotic components — all living organisms including producers (plants), consumers (animals), and decomposers (bacteria, fungi). (2) Abiotic components — the non-living physical and chemical factors such as sunlight, temperature, water, soil, minerals, and air.

Q2. Distinguish between autotrophs and heterotrophs.

Autotrophs (producers) are organisms that can synthesise their own food from inorganic substances using sunlight (photosynthesis) or chemical energy (chemosynthesis). Examples: green plants, algae, and some bacteria. Heterotrophs (consumers) are organisms that cannot make their own food and depend on autotrophs or other organisms for their nutrition. Examples: all animals, fungi, and most bacteria. Heterotrophs are further classified as herbivores (plant-eaters), carnivores (meat-eaters), omnivores (eat both), and decomposers (feed on dead matter).

Q3. What is a food chain? Give an example.

A food chain is a linear sequence of organisms through which energy and nutrients flow from producers to consumers. Each organism in the chain feeds on the one before it and is eaten by the one after it. Each step is called a trophic level. Example: Grass (producer) -> Deer (primary consumer/herbivore) -> Tiger (secondary consumer/carnivore). Energy flows from the sun through producers and then through successive consumers. A food chain typically has 3-5 trophic levels because energy is lost at each transfer.

Q4. What is the difference between a food chain and a food web?

A food chain is a single, linear sequence showing energy flow from producers to top consumers (e.g., grass -> deer -> tiger). A food web is a complex network of many interconnected food chains within an ecosystem, showing all the feeding relationships. In nature, most organisms eat more than one type of food and are eaten by multiple predators, so food webs more accurately represent ecosystem dynamics. A food web provides greater stability to the ecosystem because if one food source fails, organisms can rely on alternatives.

Q5. What are the major biomes of the world?

The major biomes are: (1) Tropical rainforest — hot, wet, near the equator, highest biodiversity. (2) Savanna (tropical grassland) — distinct wet and dry seasons, scattered trees. (3) Desert — very low rainfall, extreme temperatures, sparse vegetation. (4) Mediterranean (chaparral) — hot dry summers, mild wet winters, drought-resistant shrubs. (5) Temperate grassland (steppe/prairie) — moderate rainfall, fertile soil, grasses. (6) Temperate deciduous forest — moderate climate, trees that shed leaves in winter. (7) Taiga (boreal forest) — long cold winters, coniferous trees. (8) Tundra — near the poles, permafrost, lichens and mosses.

Q6. What is an ecological pyramid? Name the three types.

An ecological pyramid is a graphical representation showing the relationship between different trophic levels in an ecosystem — the relative amounts of energy, number of organisms, or biomass at each level. The three types are: (1) Pyramid of Numbers — shows the number of organisms at each trophic level (usually upright, but can be inverted, e.g., in a parasitic food chain). (2) Pyramid of Biomass — shows the total biomass (mass of living matter) at each trophic level (can be inverted in aquatic ecosystems). (3) Pyramid of Energy — shows the energy available at each trophic level (always upright, because energy decreases at each level according to the 10% law).

Q7. What is biodiversity? Why is it important?

Biodiversity refers to the variety of life on Earth at all levels — genetic diversity within species, species diversity within ecosystems, and ecosystem diversity within regions. It is important because: (1) It maintains ecosystem stability — diverse ecosystems are more resilient to disturbances. (2) It provides food, medicine, and raw materials. (3) It supports essential ecological processes like pollination, seed dispersal, and nutrient cycling. (4) It has cultural, aesthetic, and recreational value. (5) Loss of biodiversity can disrupt food webs and lead to ecosystem collapse, threatening human survival.

Q8. Name the three types of ecological pyramids and state which one is always upright.

The three types of ecological pyramids are: (1) Pyramid of Numbers — represents the number of organisms at each trophic level. (2) Pyramid of Biomass — represents the total dry weight of organisms at each trophic level. (3) Pyramid of Energy — represents the energy available at each trophic level. The pyramid of energy is always upright because energy always decreases at each successive trophic level (10% law). The pyramids of numbers and biomass can sometimes be inverted — for example, a pyramid of numbers is inverted in a parasitic food chain (one tree supports many insects), and a pyramid of biomass is inverted in some aquatic ecosystems (phytoplankton reproduce rapidly but have low standing biomass).

VI. Detailed Answer Questions (5 marks)

Q1. Describe the major biomes of the world — their location, climate, vegetation, and wildlife.

Biomes are large, distinct ecological regions characterised by specific climate, soil, vegetation, and wildlife:

1. Tropical Rainforest: Located near the equator (Amazon Basin, Congo Basin, Southeast Asia). Climate: Hot and wet year-round (25-28 degrees Celsius, rainfall over 200 cm/year). Vegetation: Multi-layered with emergent trees, dense canopy, understory, and forest floor. Dominated by broad-leaved evergreen trees, epiphytes, lianas, and ferns. Wildlife: Greatest biodiversity — jaguars, orangutans, toucans, poison dart frogs, countless insects. Soils are nutrient-poor due to rapid nutrient cycling.

2. Savanna (Tropical Grassland): Located between tropical forests and deserts (East Africa, Brazilian Highlands, Northern Australia). Climate: Distinct wet and dry seasons, warm year-round (25-30 degrees Celsius), rainfall 50-150 cm/year. Vegetation: Tall grasses with scattered trees (baobab, acacia). Wildlife: Large herbivores (zebras, wildebeest, elephants, giraffes) and carnivores (lions, cheetahs). Fire is a natural part of this biome.

3. Desert: Located around 30 degrees N and S latitude (Sahara, Arabian, Thar, Atacama, Mojave). Climate: Extremely low rainfall (less than 25 cm/year), hot days (up to 50 degrees Celsius) and cold nights. Vegetation: Sparse — cacti, xerophytes, thorny shrubs, deep-rooted plants. Wildlife: Camels, lizards, snakes, scorpions, insects — all adapted to conserve water and tolerate heat.

4. Mediterranean (Chaparral): Located around the Mediterranean Sea, California, central Chile, parts of South Africa and Australia. Climate: Hot, dry summers and mild, wet winters. Vegetation: Drought-resistant shrubs, hard-leaved (sclerophyllous) plants, olive trees, cork oak. Wildlife: Goats, sheep, rabbits, various birds and reptiles. Fire plays an important role in maintaining this biome.

5. Steppe (Temperate Grassland): Located in the interiors of continents (Eurasian Steppe, North American Prairies, South American Pampas). Climate: Moderate rainfall (25-75 cm/year), hot summers and cold winters. Vegetation: Dominated by grasses; trees are rare. Deep, fertile soils (chernozem) make these the world's breadbaskets. Wildlife: Bison, prairie dogs, coyotes, hawks.

6. Taiga (Boreal Forest): Located across northern North America, Europe, and Asia (between 50-70 degrees N). Climate: Long, cold winters and short, cool summers; moderate precipitation (40-100 cm, mostly snow). Vegetation: Dense coniferous forests (spruce, fir, pine) with needle-like leaves adapted to conserve water and shed snow. Wildlife: Moose, wolves, bears, lynx, beavers, and many migratory birds.

7. Tundra: Located near the poles (Arctic, Antarctic) and at high mountain altitudes. Climate: Extremely cold (average temperature below 0 degrees Celsius), short growing seasons (6-10 weeks), low precipitation (less than 25 cm/year, mostly snow). Permafrost (permanently frozen subsoil) prevents deep root growth. Vegetation: Low-growing lichens, mosses, dwarf shrubs, sedges, and grasses. Wildlife: Caribou, arctic foxes, polar bears, snowy owls, lemmings; many species migrate seasonally.

Q2. Explain the concept of the food chain and food web with examples. What is the 10% law?

Food Chain: A food chain is a linear sequence of organisms through which energy and nutrients flow, starting with producers and ending with top consumers. Each organism occupies a trophic level:

Example 1 (Terrestrial): Grass (Producer) -> Grasshopper (Primary Consumer) -> Frog (Secondary Consumer) -> Snake (Tertiary Consumer) -> Eagle (Top Carnivore)

Example 2 (Aquatic): Phytoplankton (Producer) -> Zooplankton (Primary Consumer) -> Small Fish (Secondary Consumer) -> Large Fish (Tertiary Consumer) -> Osprey (Top Carnivore)

In a food chain, energy flows from the sun to producers and then through successive consumers. At each trophic level, organisms use some energy for metabolic processes and release some as heat.

Food Web: A food web is a complex network of interconnected food chains within an ecosystem. It shows all the feeding relationships among organisms, recognising that most organisms eat and are eaten by multiple species. For example, a grasshopper eats grass but is also eaten by frogs, birds, and lizards. A snake may eat frogs, lizards, and mice. This interconnectedness makes ecosystems more stable because if one food source declines, organisms can switch to alternatives.

Example (Grassland food web): Grass is eaten by grasshoppers, rabbits, and deer. Grasshoppers are eaten by frogs and birds. Frogs are eaten by snakes. Rabbits and snakes are eaten by hawks. Deer are eaten by tigers. The hawk also eats frogs and snakes. This creates a web of interlinked chains.

10% Law (Lindeman's Law): Proposed by Raymond Lindeman, the 10% law states that only about 10% of the energy available at one trophic level is transferred to the next trophic level. The remaining 90% is lost as heat (during metabolism), used for life processes (movement, respiration, reproduction), or remains in undigested waste. This is why food chains rarely exceed 4-5 trophic levels — there simply isn't enough energy to sustain more. For example, if producers capture 10,000 kJ of solar energy, only about 1,000 kJ reaches primary consumers, 100 kJ reaches secondary consumers, and just 10 kJ reaches tertiary consumers.

Q3. Explain ecological pyramids — types, significance, and limitations.

Ecological pyramids are graphical representations showing the relationship between organisms at different trophic levels in an ecosystem. They are typically drawn with producers at the base and top carnivores at the apex.

Pyramid of Numbers: Shows the number of individual organisms at each trophic level. In a grassland ecosystem, it is typically upright — many grasses (producers), fewer herbivores (deer, rabbits), even fewer carnivores (foxes), and very few top carnivores (tigers). However, it can be inverted: in a parasitic food chain, a single tree (one producer) supports many insects (primary consumers), which support even more parasites (secondary consumers), making the pyramid top-heavy.

Pyramid of Biomass: Shows the total biomass (mass of living matter) at each trophic level. In most terrestrial ecosystems, it is upright because producers (plants) have the greatest biomass and it decreases at each level. However, in aquatic ecosystems, it can be inverted — phytoplankton (producers) have very low standing biomass at any given time because they are rapidly consumed by zooplankton, even though their total annual production is very high.

Pyramid of Energy: Shows the energy available at each trophic level. This pyramid is always upright because energy always decreases at each successive trophic level according to the 10% law. It is the most fundamental and accurate pyramid because it accounts for the rate of energy flow rather than standing crop.

Significance: Ecological pyramids show that producers form the base and support all other life. They demonstrate the 10% energy transfer law and explain why top carnivores are few in number. They also illustrate the importance of conserving producers and the vulnerability of top-level consumers.

Limitations: (1) Pyramids of numbers do not account for the size of organisms — one tree and one insect count equally. (2) Pyramids of numbers and biomass can be inverted, which is misleading. (3) Pyramids do not show the rate of production (turnover), only standing crop. (4) They do not account for omnivores that feed at multiple trophic levels. (5) Detritivores and decomposers are often excluded from pyramids even though they play a vital role.

Q4. Discuss biodiversity — its types, importance, threats, and conservation measures.

Types of Biodiversity: 1. Genetic diversity — variation in genes within a single species, enabling adaptation to changing environments (e.g., different varieties of rice). 2. Species diversity — variety of species in a given area (e.g., the Western Ghats have high species diversity). 3. Ecosystem diversity — variety of ecosystems in a region (e.g., India has deserts, forests, wetlands, mountains, and coastal ecosystems).

Importance of Biodiversity: 1. Ecological stability — diverse ecosystems are more resilient to disturbances such as disease, drought, and climate change. 2. Food security — thousands of plant and animal species provide food for humans; genetic diversity in crops prevents total crop failure. 3. Medicine — many medicines come from natural sources (e.g., quinine from cinchona, aspirin from willow bark, penicillin from fungi). 4. Economic value — forests, fisheries, and wildlife support livelihoods and industries (tourism, agriculture, pharmaceuticals). 5. Ecosystem services — pollination by bees, water purification by wetlands, soil formation by organisms, carbon sequestration by forests, flood control by mangroves. 6. Cultural and aesthetic value — biodiversity has spiritual, recreational, and educational significance.

Threats to Biodiversity: 1. Habitat destruction — deforestation, urbanisation, agriculture, and mining destroy natural habitats, which is the biggest threat. 2. Pollution — air, water, and soil pollution harm organisms and ecosystems (e.g., oil spills, plastic pollution, pesticide run-off). 3. Climate change — rising temperatures, changing rainfall patterns, and extreme weather events disrupt habitats and species. 4. Overexploitation — overfishing, poaching, and unsustainable harvesting deplete species faster than they can recover. 5. Invasive species — non-native species can outcompete, prey on, or introduce diseases to native species (e.g., water hyacinth in Indian lakes). 6. Deforestation — clearing forests for agriculture, logging, and development destroys habitats and reduces carbon sequestration.

Conservation Measures: 1. In-situ conservation — protecting species in their natural habitats through national parks, wildlife sanctuaries, biosphere reserves, and protected areas (e.g., Jim Corbett National Park, Nilgiri Biosphere Reserve). 2. Ex-situ conservation — protecting species outside their natural habitats through zoos, botanical gardens, seed banks, and cryopreservation (e.g., Svalbard Global Seed Vault). 3. Legal protection — enforcing wildlife protection laws (Wildlife Protection Act 1972 in India), banning poaching and illegal trade. 4. Sustainable use — practising sustainable agriculture, forestry, and fishing that do not deplete resources. 5. Awareness and education — promoting environmental education, eco-tourism, and community participation in conservation. 6. International cooperation — conventions like CITES (Convention on International Trade in Endangered Species), CBD (Convention on Biological Diversity), and IUCN Red List to track and protect threatened species globally.

Q5. Explain the concept of the biosphere and the interaction between its components.

The Biosphere: The biosphere is the narrow zone of the Earth where living organisms exist — the intersection of the lithosphere (land), hydrosphere (water), and atmosphere (air). It extends from the deepest ocean trenches (about 11 km below sea level) to the highest mountain peaks where organisms can survive (about 8 km above sea level), and includes all life from deep-sea vents to high-altitude bacteria. The biosphere is unique to Earth as no other planet is known to support life.

Interaction Between Components: Life in the biosphere depends on continuous interaction between biotic (living) and abiotic (non-living) components:

1. Lithosphere and Biosphere: The lithosphere (rock, soil, minerals) provides the substrate for plant growth, anchoring roots and supplying nutrients. Soil microorganisms decompose organic matter and recycle nutrients. Soil type determines vegetation, which in turn determines the animal communities that can live there. Earthworms and burrowing animals aerate and enrich soil.

2. Hydrosphere and Biosphere: Water is essential for all life — it is a major component of cells, a solvent for biochemical reactions, and a habitat for aquatic organisms. The water cycle (evaporation, condensation, precipitation, runoff) continuously replenishes freshwater. Plants transpire water, contributing to atmospheric moisture and rainfall. Marine organisms produce over 50% of the Earth's oxygen through photosynthesis.

3. Atmosphere and Biosphere: The atmosphere provides gases essential for life — oxygen for respiration, carbon dioxide for photosynthesis, and nitrogen for protein synthesis (after fixation by bacteria). The atmosphere also regulates temperature (greenhouse effect), filters harmful UV radiation (ozone layer), and drives weather and climate patterns that determine the distribution of biomes. Plants absorb CO2 and release O2 through photosynthesis; animals and decomposers absorb O2 and release CO2 through respiration — maintaining the balance of atmospheric gases.

4. Energy Flow: Solar energy enters the biosphere through photosynthesis by producers. This energy flows through food chains and food webs from producers to consumers to decomposers. At each transfer, approximately 90% of energy is lost as heat (10% law), making energy flow unidirectional — unlike nutrients, which cycle.

5. Nutrient Cycling: Unlike energy, nutrients (carbon, nitrogen, phosphorus, water) cycle between biotic and abiotic components in biogeochemical cycles. Decomposers play a critical role by breaking down dead organic matter and returning nutrients to the soil, air, and water, making them available again for producers. Without this cycling, life would deplete available nutrients.

The biosphere is thus a dynamic, self-regulating system where living organisms and their physical environment constantly interact, exchange energy and matter, and maintain the conditions necessary for life.

Common Mistakes

1. Confusing autotrophs and decomposers: Autotrophs (producers) make their own food using sunlight. Decomposers (bacteria, fungi) break down dead organic matter — they are heterotrophs, not autotrophs. They occupy different roles in the ecosystem.

2. Saying the pyramid of numbers is always upright: The pyramid of numbers can be inverted. In a parasitic food chain (one tree -> many insects -> more parasites), the pyramid is top-heavy. Only the pyramid of energy is always upright.

3. Confusing taiga and tundra: The taiga (boreal forest) is dominated by coniferous trees with long cold winters and moderate precipitation. The tundra is treeless with permafrost, extremely cold, and very short growing seasons. The taiga lies south of the tundra.

4. Thinking food chains and food webs are the same: A food chain is a single, linear path of energy flow. A food web is a complex, interconnected network of many food chains. Food webs more accurately represent real ecosystems because most organisms have multiple food sources.

5. Forgetting that decomposers are essential in ecosystems: Decomposers (bacteria, fungi) break down dead organic matter and recycle nutrients back into the soil. Without decomposers, nutrients would remain locked in dead organisms, and producers would run out of essential minerals. They are often overlooked but are critical for nutrient cycling.

6. Confusing savanna and steppe: Savanna is a tropical grassland with distinct wet and dry seasons, scattered trees (acacia, baobab), and large herbivores. Steppe is a temperate grassland with moderate rainfall, cold winters, and no scattered trees. Both are grasslands but in different climate zones.

7. Stating that biodiversity only refers to species count: Biodiversity has three levels — genetic diversity (within species), species diversity (number of species), and ecosystem diversity (variety of ecosystems). A complete understanding of biodiversity requires all three levels.

Exam Checklist

• [ ] Can define biosphere and explain its interaction with lithosphere, hydrosphere, and atmosphere
• [ ] Can distinguish between biotic and abiotic components with examples
• [ ] Can define and give examples of autotrophs, heterotrophs, and decomposers
• [ ] Can explain food chains and food webs with examples
• [ ] Can state and explain the 10% law of energy transfer (Lindeman's Law)
• [ ] Can describe the three types of ecological pyramids and identify which is always upright
• [ ] Can name and describe all major biomes (tropical rainforest, savanna, desert, Mediterranean, steppe, taiga, tundra)
• [ ] Can explain the three types of biodiversity (genetic, species, ecosystem)
• [ ] Can list threats to biodiversity and conservation measures (in-situ and ex-situ)
• [ ] Can distinguish between in-situ and ex-situ conservation with examples
• [ ] Can explain nutrient cycling and energy flow in ecosystems
• [ ] Can describe the climate, vegetation, and wildlife of each major biome

Internal Links

• [Class 9 Social Science — Biosphere Guide](/school/tamil-nadu-state-board/class/9/social/biosphere)
• [All Class 9 Social Solutions](/school/tamil-nadu-state-board/class/9/social/solutions)
• [Class 9 Social Science Subject Guide](/school/tamil-nadu-state-board/class/9/social)