Natural Resources and Environment

Ecosystem: Structure and Function

An ecosystem is a self-sustaining functional unit of nature where living organisms (biotic components) interact with each other and with their physical environment (abiotic components). It includes all biotic and abiotic factors in an area.

Components of an Ecosystem

Abiotic (non-living) factors:

• Sunlight: Primary energy source for almost all ecosystems
• Temperature: Affects enzyme activity and distribution of species
• Water: Essential for all life — determines which organisms can survive
• Soil: Provides minerals and anchorage for plants
• Air: Provides oxygen (for respiration) and carbon dioxide (for photosynthesis)
• Minerals and nutrients: Required for growth

Biotic (living) factors:

• Producers (Autotrophs): Green plants, algae — produce their own food via photosynthesis; form the base of all food chains
• Consumers (Heterotrophs): Cannot make their own food — depend on others
  • Primary consumers (Herbivores): Eat producers — e.g., rabbit, deer, cow
  • Secondary consumers (Carnivores): Eat herbivores — e.g., fox, snake, frog
  • Tertiary consumers (Top carnivores): Eat other carnivores — e.g., eagle, lion
  • Omnivores: Eat both plants and animals — e.g., human, bear, crow
• Decomposers (Saprotrophs): Fungi, bacteria — break down dead organic matter into simpler substances (returning nutrients to soil). Without decomposers, dead matter would accumulate.

Note: Decomposers and detritivores (earthworms, dung beetles) are called reducers — they are essential for recycling nutrients.

Food Chain and Food Web

Food chain: A linear sequence showing “who eats whom.” Energy flows from producers → primary consumers → secondary consumers → tertiary consumers.

Example: Grass → Grasshopper → Frog → Snake → Eagle

Producers (grass) → Primary consumers (grasshopper) → Secondary consumers (frog) → Tertiary consumers (snake) → Top carnivore (eagle)

10% Rule: Only about 10% of energy is passed from one trophic level to the next. The remaining 90% is lost as heat (respiration) and used for life processes. This limits the number of trophic levels to 4–5.

Food web: In nature, organisms eat more than one type of food and are eaten by more than one predator — this creates a complex food web (not a simple chain). Food webs are more realistic and stable.

Ecological Pyramids

Pyramid of numbers: Number of organisms at each trophic level (numbers decrease as you go up).

Pyramid of energy: Energy at each trophic level (always upright — less energy available at higher levels).

Pyramid of biomass: Dry weight of organisms at each trophic level. Usually upright, but can be inverted (e.g., in a single tree supporting many insects — more consumers than producers).

Biogeochemical Cycles

Elements (C, N, P, H, O) are continuously cycled between living organisms (biotic pool) and non-living environment (abiotic pool). These are called biogeochemical cycles (bio = living; geo = earth; chemical = elements).

Water Cycle (Hydrological Cycle)

Evaporation (from oceans, lakes, rivers)
        ↓
    Transpiration (from plants)
        ↓
Cloud formation (condensation)
        ↓
Precipitation (rain, snow, hail)
        ↓
Run-off → Rivers → Ocean / Infiltration → Groundwater

• Evaporation: Water from oceans/lakes heated by sun → water vapor rises
• Transpiration: Water absorbed by plant roots is released as vapor through stomata
• Condensation: Water vapor rises, cools, forms clouds
• Precipitation: When water droplets in clouds become heavy enough → rain
• Runoff and infiltration: Water returns to oceans

Carbon Cycle

• Photosynthesis: CO₂ from atmosphere → glucose (organic compounds) in plants
• Respiration: Plants and animals break down glucose → CO₂ released back to atmosphere
• Decomposition: Decomposers break down dead matter → CO₂ released
• Combustion: Burning fossil fuels (coal, oil, natural gas) and wood → CO₂ added to atmosphere (main cause of global warming)
• Carbon sink: Oceans absorb CO₂; forests absorb CO₂ (photosynthesis) — called carbon sinks

The Greenhouse Effect: CO₂, methane (CH₄), water vapor, and other gases trap heat in Earth’s atmosphere, keeping Earth warm enough for life. But excessive CO₂ from burning fossil fuels enhances the greenhouse effect → global warming.

Nitrogen Cycle

• Nitrogen fixation: Atmospheric N₂ (78% of air, but unusable by most organisms) is converted to usable forms:
  • Biological: Nitrogen-fixing bacteria (Rhizobium in root nodules of legumes) convert N₂ → NH₃ (ammonia)
  • Lightning: High energy converts N₂ → NO (nitric oxide)
  • Industrial: Haber-Bosch process (fertilizer factory) converts N₂ to ammonia → fertilizers
• Nitrification: NH₃ → Nitrite (NO₂⁻) → Nitrate (NO₃⁻) — by nitrifying bacteria (Nitrosomonas, Nitrobacter)
• Assimilation: Plants absorb nitrates from soil → incorporate into proteins and nucleic acids
• Ammonification: Decomposers break down dead organisms and waste → NH₃ released back
• Denitrification: Anaerobic bacteria convert nitrates back to N₂ → released to atmosphere

Oxygen Cycle

• Photosynthesis: O₂ released as byproduct (produces O₂)
• Respiration: All organisms consume O₂ → CO₂ released
• Decomposition: Also consumes O₂
• Ozone formation: O₂ → O + O (UV radiation) → O₃ (ozone in stratosphere)
• Ozone depletion: CFCs (chlorofluorocarbons) break down O₃ → O₂ + O, reducing the ozone layer — leads to more UV radiation reaching Earth

Environmental Issues

Air Pollution

Major pollutants:

• Suspended Particulate Matter (SPM): Dust, smoke, pollen — causes respiratory diseases
• Sulfur dioxide (SO₂): From burning coal, petrol — causes acid rain (damages buildings, trees, water bodies)
• Nitrogen oxides (NOx): From vehicles, power plants — causes smog (brown haze), respiratory problems
• Carbon monoxide (CO): From incomplete combustion (vehicle exhaust) — binds to hemoglobin, reduces oxygen-carrying capacity
• Lead: From vehicle exhaust (leaded petrol) — neurological damage, especially in children

Smog: Combination of smoke and fog. Classical smog (London-type: SO₂ + smoke) — industrial. Photochemical smog (Los Angeles-type: NOx + hydrocarbons + sunlight) — urban vehicle pollution, causes eye irritation, crop damage.

Water Pollution

Sources:

• Industrial waste: Heavy metals (mercury, lead), chemicals ( dyes, acids)
• Agricultural runoff: Pesticides (DDT, endosulfan), fertilizers (nitrogen, phosphorus) → eutrophication (excessive nutrient enrichment → algal bloom → oxygen depletion → fish die)
• Sewage: Domestic waste → pathogens (cholera, typhoid, dysentery)
• Oil spills: Marine ecosystems destroyed (e.g., Exxon Valdez, Deepwater Horizon)

Bio-magnification: Some pollutants (like DDT) accumulate in organisms’ bodies at higher concentrations as you go up the food chain. Example: DDT in water → algae → small fish → large fish → birds (concentration increases at each level). This caused eggshell thinning in birds (pesticides in fish-eating birds) → bald eagles nearly extinct → DDT banned in USA (1972).

Soil Pollution

• Pesticides and fertilizers: Persistent in soil, reduce soil fertility, harm earthworms and microorganisms
• Plastic: Non-biodegradable — remains in soil for centuries; creates microplastics
• Industrial waste: Heavy metals contaminate soil, making it unfit for agriculture
• Solid waste: Dumping in open areas, landfills overflowing

Solid waste management: The biggest challenge. The 4 R’s: Refuse (avoid use), Reduce (less packaging), Reuse (use again), Recycle (convert to new product).

Global Warming and Climate Change

• Greenhouse gases: CO₂, methane (CH₄), nitrous oxide (N₂O), water vapor
• CO₂ from burning fossil fuels (coal, oil, natural gas) is the largest contributor
• These gases trap heat → Earth’s average temperature rising
• Paris Agreement (2015): World leaders agreed to limit global warming to 1.5–2°C above pre-industrial levels

Effects of global warming:

• Melting of polar ice caps → sea level rise → coastal flooding
• Changes in rainfall patterns → more droughts and floods
• Coral bleaching (warmer oceans → bleaching of coral reefs)
• Migration of species poleward
• Increased frequency of extreme weather events (cyclones, heatwaves)

Ozone Depletion

• The ozone layer in the stratosphere (20–35 km above Earth) absorbs harmful UV-B and UV-C radiation
• CFCs (used in refrigerators, AC, spray cans) drift up and break down ozone → O₃ → O₂ + O
• Montreal Protocol (1987): Global agreement to phase out CFCs — success story of international cooperation
• Ozone hole was most visible over Antarctica — recovering slowly

Biodiversity Loss

Biodiversity: The variety of life on Earth — genes, species, and ecosystems. India is one of the 17 megadiverse countries (home to 2 of 36 global biodiversity hotspots).

Causes of biodiversity loss:

1. Habitat destruction: Deforestation, construction, agriculture — biggest cause
2. Invasive species: Introduced species outcompete native species
3. Overexploitation: Overhunting, overfishing
4. Climate change: Shifting habitats faster than species can adapt
5. Pollution: Chemical contamination

Conservation:

• In-situ: Protected areas (national parks, wildlife sanctuaries), biosphere reserves, sacred grooves, Community Reserves
• Ex-situ: Zoos, botanical gardens, seed banks, gene banks, tissue culture

Wildlife Protection Act (1972): Provides protection to wild animals and plants; Schedule I species (tigers, elephants, pandas) have highest protection.

CTET Exam Focus

• Ecosystem: Biotic (producers, consumers, decomposers) and abiotic (sunlight, temperature, water, soil)
• Food chain: 10% energy rule, trophic levels
• Biogeochemical cycles: Water cycle (evaporation → transpiration → precipitation → runoff), Carbon cycle (photosynthesis ↔ respiration), Nitrogen cycle (nitrogen fixation by bacteria)
• Environmental issues: Air pollution (SO₂, NOx, CO, lead), water pollution (eutrophication, bio-magnification of DDT), soil pollution
• Global warming: Greenhouse gases, CO₂ from fossil fuels, Paris Agreement targets
• Ozone depletion: CFCs, Montreal Protocol, ozone hole
• Biodiversity loss and conservation: In-situ (national parks), ex-situ (seed banks), Wildlife Protection Act 1972

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