Ecology and Environment
1. Introduction
Ecology studies the interactions between organisms and their environment. Environmental issues such as pollution and climate change are critical global challenges requiring urgent action.
2. Ecosystem Structure
An ecosystem includes all living (biotic) and non-living (abiotic) components in an area.
2.1 Components
Abiotic: Sunlight, temperature, water, soil, air, nutrients. Biotic: Producers (autotrophs), consumers (herbivores, carnivores, omnivores), decomposers (bacteria, fungi).
2.2 Types of Ecosystems
Natural: Forest, grassland, desert, aquatic (freshwater, marine). Artificial: Cropland, aquarium, garden.
3. Energy Flow
Source: Sun (primary energy source). Only ~1% of solar energy is captured by photosynthesis.
Energy flows in one direction (unidirectional) through trophic levels. About 10% of energy is transferred to the next level (10% law — Lindeman).
4. Food Chain and Food Web
4.1 Food Chain
Linear sequence: Grass → Grasshopper → Frog → Snake → Hawk (grazing food chain).
Detritus food chain: Dead organic matter → Detritivores → Predators.
4.2 Food Web
Interconnected food chains. More stable than individual food chains.
5. Ecological Pyramids
5.1 Pyramid of Numbers
Number of organisms at each trophic level. Upright (grassland) or inverted (tree ecosystem).
5.2 Pyramid of Biomass
Total dry weight at each level. Generally upright. Inverted in aquatic ecosystems (phytoplankton < zooplankton).
5.3 Pyramid of Energy
Always upright. Shows energy flow. Only ~10% transfers to the next level.
6. Biodiversity
Variety of living organisms at genetic, species, and ecosystem levels.
6.1 Levels
Genetic diversity: Variation within species. Species diversity: Variety of species. Ecosystem diversity: Variety of habitats.
6.2 Hotspots
Areas with high endemism and threat. India has four: Western Ghats, Himalayas, Indo-Burma, Sundaland.
6.3 Conservation
In situ: National parks, wildlife sanctuaries, biosphere reserves. Ex situ: Zoos, botanical gardens, seed banks, gene banks.
7. Environmental Issues
7.1 Pollution
Air: SO₂, NOₓ, CO, particulates. Effects: Acid rain (pH < 5.6), smog, respiratory diseases.
Water: Eutrophication (excess nutrients → algal bloom → oxygen depletion). Industrial effluents, sewage.
Soil: Pesticides, herbicides, industrial waste. Bioaccumulation (DDT in food chain).
Noise: > 80 dB causes hearing loss, stress.
7.2 Global Warming and Climate Change
Increase in greenhouse gases (CO₂, CH₄, N₂O, CFCs, water vapour). Effects: Rising sea levels, extreme weather, melting glaciers.
7.3 Ozone Depletion
CFCs (chlorofluorocarbons) destroy ozone (O₃) in the stratosphere. Ozone hole over Antarctica. Effects: Increased UV-B radiation (skin cancer, cataracts, reduced photosynthesis).
Montreal Protocol (1987): Phased out CFCs. Successful international environmental agreement.
8. Worked Problems
Problem 1: Calculate the energy available at the tertiary consumer level if producers fix 50,000 kJ of energy. Solution: 10% → Primary consumer: 5,000 kJ. 10% → Secondary consumer: 500 kJ. 10% → Tertiary consumer: 50 kJ.
9. Common Mistakes
'Students often think the pyramid of energy can be inverted. It is always upright because energy decreases at each trophic level due to metabolic losses.'
10. ISC Exam Focus
| Topic | Theory Marks | Practical Marks |
|---|---|---|
| Ecosystem and energy flow | 3 | 2 |
| Ecological pyramids | 2 | 1 |
| Biodiversity | 3 | 2 |
| Environmental issues | 4 | 2 |
11. Self-Test Questions
- Explain the 10% law of energy transfer with an example.
- Differentiate between in situ and ex situ conservation with examples.
- What is eutrophication? How does it affect aquatic ecosystems?
- Explain how CFCs cause ozone depletion. What is the Montreal Protocol?
- Describe the structure of a forest ecosystem with its components.
