Environmental Science Exam Revision: Key Concepts and Acts

Posted on Mar 14, 2026 in Biology

Environmental Science Exam Revision

This document consolidates critical definitions, concepts, years, and frequently asked questions for Units 3, 4, 5, and 7 to optimize your exam preparation.

Unit 3: Ecosystems and Ecosystem Services

Key Terms and Pioneers

  • Ecosystem: Term coined by A.G. Tansley (1935). It is the smallest structural and functional unit of ecology.
  • Ecology: Term coined by E. Haeckel.
  • Ecotone: The transition zone where two different ecosystems meet (e.g., estuary). Species abundant here are called edge species.
  • Biosphere: The largest unit of the ecosystem.

Ecosystem Structure

  • Abiotic (Non-living): Temperature, light, water, edaphic factors (soil), and minerals.
  • Biotic (Living):
    • Producers (Autotrophs): Green plants, Phytoplankton (primary producers in a pond). Heliophytes grow in direct sun; Xerophytes grow in dry places.
    • Consumers (Heterotrophs): Herbivores (primary), Carnivores (secondary/tertiary).
    • Decomposers (Saprotrophs): Bacteria and Fungi. They are nature’s cleaners.

Energy Flow and Food Chains

  • Energy Flow: The primary source is the Sun. Flow is always unidirectional and does not cycle.
  • 10% Law: Only about 10% of energy transfers from one trophic level to the next; the rest is lost as heat via respiration.
  • Food Chains: Grazing (starts with plants) vs. Detritus (starts with dead organic matter).
  • Food Web: A complex network of interconnected food chains that increases ecosystem stability.

Ecological Pyramids and Succession

  • Pyramid of Energy: Always upright.
  • Pyramid of Numbers: Upright in grasslands; absent or inverted in forests or parasitic chains.
  • Pyramid of Biomass: Upright in terrestrial ecosystems; inverted in pond ecosystems.
  • Ecological Succession: Directional change in a community over time. Sequence: Nudation → Invasion → Ecesis → Completion → Reaction → Climax. Pioneer species in xerarch succession are Lichens.

Unit 4: Biodiversity and Conservation

Core Concepts

  • Biodiversity: Term coined by W.G. Rosen.
  • Levels: Genetic, Species (alpha diversity), and Ecosystem diversity.
  • Mega-diversity: India is one of 17 nations with 10 bio-geographical zones. Maximum diversity is found in Coral reefs and Tropical Rain Forests.

Species Classifications

  • Endemic Species: Confined to a specific geographic area (e.g., Lion-tailed macaque).
  • Endangered Species: High risk of extinction (e.g., Red Panda, Asiatic Lion).
  • Red Data Book: Published by the IUCN for threatened species.

Biodiversity Hotspots

  • Term coined by Norman Myers. Hotspots are regions with extreme species richness and high endemism. There are 36 globally; India has 4.

Conservation Methods

  • In-situ (On-site): Protecting species in natural habitats (e.g., National Parks, Wildlife Sanctuaries, Biosphere Reserves).
  • Ex-situ (Off-site): Protecting species outside natural habitats (e.g., Zoos, Botanical Gardens, Seed Banks, Cryopreservation).

Unit 5: Environmental Pollution and Management

Pollutants

  • Primary: Emitted directly (e.g., CO, SO2, NOX, Fly Ash).
  • Secondary: Formed by atmospheric reactions (e.g., Ozone, PAN).
  • Biomagnification: Accumulation of toxic chemicals (like DDT) at higher trophic levels.

Air and Noise Pollution

  • Smog: Smoke and fog; caused by nitrogen oxides and vehicle emissions.
  • Acid Rain: Caused by SO2 and NO2; leads to “Marble Cancer” in monuments.
  • Bhopal Gas Tragedy (1984): Leak of MIC (Methyl Isocyanate).
  • Noise Pollution: Measured in Decibels (dB).

Water Pollution

  • BOD: Biochemical Oxygen Demand; high BOD indicates highly polluted water.
  • Eutrophication: Nutrient enrichment causing algal blooms and oxygen depletion.
  • Heavy Metal Diseases: Mercury (Minamata), Cadmium (Itai-Itai), Arsenic (Black foot), Nitrates (Blue-baby syndrome), Fluoride (Fluorosis).

Solid Waste Management

  • 3 R Principle: Reduce, Reuse, Recycle.
  • Landfills: Commonly release Methane gas.

Unit 7: Environmental Treaties and Legislation

Major Indian Acts

  • 1972: Wildlife (Protection) Act
  • 1974: Water (Prevention and Control of Pollution) Act
  • 1980: Forest (Conservation) Act
  • 1981: Air (Prevention and Control of Pollution) Act
  • 1986: Environment (Protection) Act

International Protocols

  • Stockholm (1972): First international environment conference.
  • Ramsar (1971): Wetlands conservation.
  • Montreal (1987): Ozone layer protection (phasing out CFCs).
  • Earth Summit (1992): Agenda 21 and CBD.
  • Kyoto (1997): Greenhouse gas reduction.
  • Paris (2015): Limit global warming to below 2°C.