Biosphere — Class 9 Social Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 9 Social Science, Geography — Chapter 5. Life on Earth — ecosystems, biomes, and biodiversity.
1. About this lesson
The biosphere is the zone where life exists — where the lithosphere, atmosphere, and hydrosphere meet. This chapter covers ecosystems, biomes, food chains, biodiversity, and conservation.
2. Ecosystem
An ecosystem is a community of living organisms interacting with each other and their non-living environment.
Components
| Component | Description | Examples |
|---|---|---|
| Biotic (Living) | All living organisms | Plants, animals, microorganisms |
| Abiotic (Non-living) | Physical and chemical factors | Sunlight, temperature, water, soil, air |
Biotic Classification by Role
| Type | Role | Examples |
|---|---|---|
| Producers (Autotrophs) | Make their own food (photosynthesis) | Green plants, algae, phytoplankton |
| Consumers (Heterotrophs) | Eat other organisms | Herbivores (primary), Carnivores (secondary), Omnivores |
| Decomposers (Saprotrophs) | Break down dead matter → nutrients | Bacteria, fungi |
3. Food Chain and Food Web
- Food Chain: Linear sequence of who eats whom (Grass → Grasshopper → Frog → Snake → Eagle).
- Trophic Levels: Each step in a food chain.
- Food Web: Interconnected food chains in an ecosystem.
- Energy flow is unidirectional (Sun → producers → consumers) and decreases at each level (~10% transferred — Lindeman's Law).
4. Biomes
A biome is a large geographical region with a distinct climate, vegetation, and animal life.
| Biome | Climate | Vegetation | Animals | Location |
|---|---|---|---|---|
| Tropical Rainforest | Hot, humid, heavy rainfall | Dense, evergreen, tall trees; multiple layers | Monkeys, parrots, jaguars, insects | Amazon, Congo, SE Asia |
| Tropical Savanna (Grassland) | Warm, seasonal rain | Tall grasses, scattered trees | Lions, zebras, giraffes, elephants | Africa (Serengeti), Brazil, Australia |
| Desert | Hot days, cold nights; very low rainfall | Cacti, thorny bushes; xerophytic adaptations | Camels, lizards, snakes, scorpions | Sahara, Thar, Kalahari |
| Temperate Grassland | Hot summer, cold winter; moderate rain | Grasses; few trees | Bison, wild horses, prairie dogs | Prairies (N America), Steppes (Eurasia), Pampas (S America), Downs (Australia), Veld (S Africa) |
| Temperate Deciduous Forest | Moderate climate; 4 seasons | Trees shed leaves in autumn | Deer, bears, foxes, squirrels | Europe, E North America, E China |
| Taiga (Coniferous/Boreal Forest) | Long, cold winter; short summer | Cone-bearing trees (pine, spruce, fir) | Moose, wolves, bears, lynx | Canada, Russia, Scandinavia |
| Tundra | Extremely cold; permafrost (frozen subsoil) | Mosses, lichens, small shrubs | Reindeer, arctic fox, polar bears, migratory birds | Arctic regions, high mountains |
5. Biodiversity
- Biodiversity: Variety of life forms on Earth — genetic, species, and ecosystem diversity.
- Biodiversity hotspots: Regions with high endemic species under threat (e.g., Western Ghats, Himalayas, Indo-Burma).
- Importance: ecological balance, food, medicine, climate regulation, cultural value.
Threats to Biodiversity
- Habitat destruction (deforestation, urbanization).
- Pollution, climate change, overexploitation (hunting, poaching).
- Invasive species.
Conservation
In-situ (in natural habitat): National Parks, Wildlife Sanctuaries, Biosphere Reserves.
Ex-situ (outside natural habitat): Zoos, botanical gardens, seed banks, gene banks.
6. Worked examples
Example 1. What are the two components of an ecosystem? Biotic (living) and Abiotic (non-living).
Example 2. Name a biome with permafrost. Tundra.
Example 3. What is a food web? Interconnected food chains in an ecosystem.
Example 4. What is the coldest biome on Earth? Tundra.
7. Book-back questions (Samacheer Kalvi)
I. Choose the correct answer
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The coldest biome on Earth is — (a) Tundra / (b) Taiga / (c) Desert / (d) Oceans. Ans: (a) Tundra.
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This is the smallest unit of biosphere — (a) Biomes / (b) Environment / (c) Ecosystems / (d) None of the above. Ans: (c) Ecosystems.
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Nutrients are recycled in the atmosphere with the help of certain micro-organisms, referred to as — (a) Producers / (b) Decomposers / (c) Consumers / (d) None of the above. Ans: (b) Decomposers. (Decomposers break down dead matter and recycle nutrients.)
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Xerophytic plants are specifically adapted to — (a) Saline and sandy / (b) Limited moisture availability / (c) Cold temperature / (d) Humid. Ans: (a) Saline and sandy. (Xerophytes are adapted to dry, desert-like conditions with saline/sandy soil.)
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Why is the usage of rainforest biomes for large scale agriculture unsustainable? — (a) too wet / (b) too warm / (c) soil too thin / (d) soil is poor. Ans: (d) soil is poor. (Rainforest soil is lateritic — nutrients washed away by heavy rain.)
II. Assertion and Reason type
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A: Heterotrophs do not produce their own food. R: They depend on autotrophs for their nourishment. — (a) Both A and R are true; R explains A.
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A: Hotspots are regions characterised by numerous endemic plants and animals in a vulnerable environment. R: To manage and focus on conservation more effectively, researchers identified hotspots. — (a) Both A and R are true; R explains A.
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A: The number of gorillas in Africa has plummeted by 60% in the past twenty years. R: Non-intervention of human beings in the forest areas. — (c) A is true; R is false. (R is false — gorilla decline is due to human intervention: poaching, habitat destruction.)
III. Fill in the blanks
- An area where animals, plants and micro-organisms live and interact with one another is known as Ecosystem.
- Consumers are also called Heterotrophs.
- Food web is a system of interlocking and interdependent food chains.
- A Biome is an extensive large ecosystem.
- The vegetative type commonly found in desert biomes is called Xerophytes.
- Estuary is an aquatic biome found where fresh water and salt water mix.
IV. Answer the following in brief
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What is Biosphere? — The biosphere is a life-supporting layer on Earth's surface encompassing the Lithosphere, Hydrosphere, and Atmosphere. It includes flora and fauna that thrive on or near the Earth's surface.
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What is an ecosystem? — A community where all living organisms live and interact with one another and with their non-living environment (land, soil, air, water). Ecosystems range from the smallest (e.g., bark of a tree) to the global ecosystem (ecosphere). Examples: cropland, pond, forest, desert ecosystems.
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What does 'biodiversity' mean? — Biodiversity or biological diversity refers to the wide variety of living organisms (plants, animals, micro-organisms) living in a habitat. It is influenced by topography, climate, and human activities.
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What is meant by loss of biodiversity? — The extinction of species (flora and fauna) due to human and natural influences. Habitat destruction (deforestation, population explosion, pollution, global warming) is the major cause. Severe habitat loss can eliminate species from the planet.
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Mention the various terrestrial biomes. — Tropical Forest Biomes, Tropical Savanna Biomes, Desert Biomes, Temperate Grassland Biomes, Tundra Biomes.
V. Give reasons
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Producers are also called autotrophs. — Producers are self-nourishing components of the ecosystem. Hence called Autotrophs. Found on land and water. Examples: Plants, Algae, Bacteria.
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Biosphere provides a stable ecosystem. — Biosphere harbours all ecosystems on Earth and sustains all life forms including mankind. Therefore it provides a stable ecosystem.
VI. Distinguish between
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Producers vs Decomposers.
- Producers: Self-nourishing (autotrophs); found on land and water; e.g., plants, algae, bacteria.
- Decomposers: Cannot prepare own food; live on dead/decaying matter (saprotrophs); e.g., fungus, mushrooms.
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Terrestrial biomes vs Aquatic biomes.
- Terrestrial: Group of living organisms interacting on land; mainly determined by temperature and rainfall. Examples: Tropical forest, savanna, desert, temperate grassland, tundra.
- Aquatic: Found in water bodies; based on salinity, depth, and temperature. Examples: Freshwater (rivers, lakes), Marine (oceans), Estuaries.
8. Common mistakes
- Mistake: Tundra has tall trees. Fix: Tundra has only mosses, lichens, small shrubs due to permafrost.
- Mistake: Decomposers are producers. Fix: Decomposers break down dead matter; producers make their own food.
- Mistake: Savanna = desert. Fix: Savanna is a tropical grassland with scattered trees and seasonal rain.
8. Quick revision
- Geography Ch 5 · Biosphere — zone of life.
- Ecosystem: Biotic (producers, consumers, decomposers) + Abiotic (sunlight, water, soil).
- Food chain: Grass → Grasshopper → Frog → Snake → Eagle. Energy decreases at each level (~10% rule).
- Biomes: Rainforest (dense, equatorial), Savanna (grassland + trees, Africa), Desert (xerophytic, Sahara/Thar), Temperate Grassland (Prairies, Steppes, Pampas), Taiga (coniferous, Canada/Russia), Tundra (mosses, permafrost, Arctic).
- Biodiversity: hotspots (Western Ghats), threats (habitat loss, pollution), conservation (in-situ: national parks; ex-situ: zoos).
