Environment and Ecosystem
Overview
Environment and Ecosystem is a foundational topic in the Science section of WB TET Paper II, bridging biology with environmental awareness. This topic tests your understanding of how living organisms interact with each other and their physical surroundings — a concept central to the upper-primary science curriculum (Classes 6–8).
For the exam, expect questions on ecosystem components, energy flow through food chains and food webs, types of biodiversity, and causes and effects of pollution. The topic also connects with pedagogy questions about environmental awareness and sustainable development. Mastering this area requires understanding both the scientific concepts and their real-world applications, particularly in the context of West Bengal's environment.
Questions typically range from straightforward definitions to application-based problems involving food chain analysis or pollution control measures.
Key Concepts
- Environment comprises all biotic (living) and abiotic (non-living) factors that surround and influence an organism — air, water, soil, temperature, plants, animals and microorganisms.
- Ecosystem is a functional unit where living organisms interact with each other and their physical environment; it can be as small as a pond or as large as a forest.
- Biotic components include producers (green plants), consumers (herbivores, carnivores, omnivores) and decomposers (bacteria, fungi).
- Abiotic components include sunlight, temperature, water, soil, minerals and atmospheric gases.
- Food chain represents a linear sequence of energy transfer: Producer → Primary Consumer → Secondary Consumer → Tertiary Consumer.
- Food web is an interconnected network of multiple food chains in an ecosystem, showing complex feeding relationships.
- Biodiversity refers to the variety of life forms at three levels — genetic diversity, species diversity and ecosystem diversity.
- Pollution is the introduction of harmful substances (pollutants) into the environment, classified as air, water, soil and noise pollution.
Formulas / Key Facts
| Concept | Key Fact |
|---|---|
| Energy flow | Only 10% of energy transfers to the next trophic level (10% Law by Lindeman) |
| Producers | Also called autotrophs; they convert solar energy to chemical energy through photosynthesis |
| Primary consumers | Herbivores that directly feed on plants (e.g., grasshopper, deer, rabbit) |
| Secondary consumers | Carnivores that feed on herbivores (e.g., frog, snake, small fish) |
| Tertiary consumers | Top predators that feed on secondary consumers (e.g., eagle, tiger, shark) |
| Decomposers | Break down dead organic matter and return nutrients to soil (bacteria, fungi) |
| Biodiversity hotspots | India has 4 hotspots — Western Ghats, Eastern Himalayas, Indo-Burma, Sundaland |
| Endemic species | Species found only in a particular region (e.g., Gangetic dolphin, Bengal tiger) |
| Air pollutants | CO, CO₂, SO₂, NO₂, particulate matter, CFCs |
| Water pollutants | Industrial effluents, sewage, pesticides, heavy metals |
| Greenhouse gases | CO₂, CH₄ (methane), N₂O, water vapour — cause global warming |
Worked Examples
Example 1: Constructing a Food Chain
Question: Arrange the following organisms into a food chain: Snake, Grass, Eagle, Grasshopper, Frog
Solution:
- Step 1: Identify the producer — Grass (makes its own food)
- Step 2: Identify primary consumer — Grasshopper (eats grass)
- Step 3: Identify secondary consumer — Frog (eats grasshopper)
- Step 4: Identify tertiary consumer — Snake (eats frog)
- Step 5: Identify top predator — Eagle (eats snake)
Food Chain: Grass → Grasshopper → Frog → Snake → Eagle
Example 2: Energy Transfer Calculation
Question: If producers in an ecosystem capture 10,000 joules of energy from sunlight, how much energy will be available to secondary consumers?
Solution:
- Energy at producer level = 10,000 J
- Energy at primary consumer level = 10% of 10,000 = 1,000 J
- Energy at secondary consumer level = 10% of 1,000 = 100 J
Answer: 100 joules
Example 3: Identifying Pollution Type
Question: A factory releases untreated chemical waste into a nearby river, causing fish to die. Identify the type of pollution and two control measures.
Solution:
- Type of pollution: Water pollution
- Control measures:
- Install effluent treatment plants (ETP) before discharge
- Regular monitoring of water quality by pollution control boards
Common Mistakes
- Confusing food chain with food web → A food chain is a single linear pathway; a food web is multiple interconnected chains. Remember: chain = one line, web = network.
- Placing decomposers at the end of food chain → Decomposers do not occupy a trophic level in the chain; they act on dead matter at ALL levels. Show them separately, connected to each level.
- Thinking energy increases at higher trophic levels → Energy DECREASES as we move up (only 10% transfers). This is why top predators are fewer in number.
- Confusing biodiversity with species count only → Biodiversity includes genetic diversity (within species), species diversity (between species) and ecosystem diversity (variety of habitats). All three matter.
- Mixing up primary and secondary pollutants → Primary pollutants are directly emitted (CO, SO₂). Secondary pollutants form by chemical reactions (ozone, smog). The exam may test this distinction.
- Forgetting local West Bengal examples → Sundarbans ecosystem, Gangetic dolphin, mangrove biodiversity are regionally relevant examples that strengthen answers.
Quick Reference
- Ecosystem = Biotic + Abiotic components interacting together
- 10% Law: Only 1/10th of energy passes to the next trophic level
- Food chain has 4–5 trophic levels maximum (energy limitation)
- Three levels of biodiversity: Genetic, Species, Ecosystem
- Four types of pollution: Air, Water, Soil, Noise
- India's biodiversity hotspots: Western Ghats, Eastern Himalayas, Indo-Burma, Sundaland