Environment and Ecosystem

Overview

Environment and Ecosystem is a foundational topic in the Science section of Bihar 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 both scientific literacy and environmental citizenship.

For Bihar TET, expect questions on ecosystem components, energy flow through food chains and food webs, ecological pyramids, and types of pollution with their causes and effects. The topic often appears with 2-4 questions and frequently connects to Bihar's local environmental issues like Ganga pollution, deforestation in the Chota Nagpur region, and air quality concerns in urban centres.

Mastery requires understanding the structural and functional aspects of ecosystems, tracing energy transfer through trophic levels, and knowing the major pollutants affecting air, water, and soil. Questions typically test conceptual clarity rather than rote memorisation.

Key Concepts

• **Environment** comprises all biotic (living) and abiotic (non-living) factors surrounding an organism, including air, water, soil, temperature, light, plants, animals, and microorganisms.

• **Ecosystem** is a self-sustaining functional unit where living organisms interact with each other and their physical environment through energy flow and nutrient cycling. Examples: pond ecosystem, forest ecosystem, grassland ecosystem.

• **Biotic components** include producers (autotrophs like green plants), consumers (herbivores, carnivores, omnivores), and decomposers (bacteria, fungi). Abiotic components include sunlight, temperature, water, soil, and minerals.

• **Food chain** represents a linear sequence of organisms where energy transfers from one trophic level to the next. Energy transfer efficiency is only about 10% at each level (10% Law by Lindeman).

• **Food web** is an interconnected network of multiple food chains, representing the complex feeding relationships in an ecosystem. It provides stability—if one species disappears, alternatives exist.

• **Ecological pyramids** graphically represent trophic structure. Pyramid of numbers shows organism count, pyramid of biomass shows dry weight, and pyramid of energy shows energy content at each level. Energy pyramids are always upright.

• **Biogeochemical cycles** describe the movement of nutrients (carbon, nitrogen, water) through biotic and abiotic components, ensuring continuous availability of essential elements.

• **Pollution** is the introduction of harmful substances (pollutants) into the environment, degrading air, water, or soil quality and affecting living organisms.

Formulas / Key Facts

| Concept | Key Fact | |---------|----------| | 10% Law | Only 10% of energy transfers from one trophic level to the next; 90% is lost as heat | | Trophic Levels | Producers → Primary Consumers → Secondary Consumers → Tertiary Consumers → Decomposers | | Oxygen in atmosphere | Approximately 21% | | Carbon dioxide in atmosphere | Approximately 0.04% (but rising due to human activities) | | Major greenhouse gases | CO₂, CH₄ (methane), N₂O, CFCs, water vapour | | BOD (Biochemical Oxygen Demand) | Measures organic pollution in water; higher BOD = more polluted water | | pH of acid rain | Below 5.6 (normal rain is slightly acidic at 5.6) | | Ozone layer location | Stratosphere (15-35 km above Earth's surface) | | Major water pollutants | Industrial effluents, sewage, pesticides, fertilizers, heavy metals | | Biomagnification | Increase in concentration of toxins (like DDT) at higher trophic levels |

Worked Examples

**Example 1: Food Chain Analysis**

*Question:* In a grassland ecosystem, grass → grasshopper → frog → snake → hawk. If grass produces 10,000 joules of energy, how much energy is available to the hawk?

*Solution:*

• Apply the 10% Law at each transfer
• Grass (Producers): 10,000 J
• Grasshopper (Primary Consumer): 10,000 × 10/100 = 1,000 J
• Frog (Secondary Consumer): 1,000 × 10/100 = 100 J
• Snake (Tertiary Consumer): 100 × 10/100 = 10 J
• Hawk (Quaternary Consumer): 10 × 10/100 = 1 J

*Answer:* The hawk receives only 1 joule of energy.

**Example 2: Identifying Trophic Levels**

*Question:* A deer eats grass. A tiger eats the deer. Bacteria decompose the dead tiger. Identify the trophic level of each organism.

*Solution:*

• Grass: Producer (T1) — makes its own food through photosynthesis
• Deer: Primary Consumer/Herbivore (T2) — eats producers directly
• Tiger: Secondary Consumer/Carnivore (T3) — eats herbivores
• Bacteria: Decomposer — breaks down dead organic matter, returns nutrients to soil

**Example 3: Pollution Type Identification**

*Question:* A factory releases SO₂ and NO₂ into the atmosphere. What type of pollution is this, and what environmental problem does it cause?

*Solution:*

• Type: Air pollution (gaseous pollutants from industrial source)
• Environmental problem: These gases combine with atmospheric moisture to form sulphuric acid (H₂SO₄) and nitric acid (HNO₃), causing **acid rain**
• Effects: Damages monuments (like Taj Mahal—marble cancer), acidifies water bodies, harms aquatic life, damages crops and forests

Common Mistakes

• **Confusing food chain with food web** → A food chain is a single linear pathway; a food web is multiple interconnected food chains. Questions may show a diagram and ask which term applies.

• **Assuming energy increases at higher trophic levels** → Energy always decreases as we move up trophic levels (10% Law). This is why top predators are fewer in number and ecosystems cannot support many trophic levels.

• **Placing decomposers at the "top" of the food chain** → Decomposers operate at all trophic levels simultaneously, breaking down dead matter from any level. They are not the final consumers but rather recyclers.

• **Confusing biomagnification with bioaccumulation** → Bioaccumulation is the buildup of toxins within a single organism over time. Biomagnification is the increase in toxin concentration across trophic levels in a food chain.

• **Thinking all ecological pyramids are upright** → Pyramid of numbers can be inverted (tree ecosystem: one tree supports many insects). Pyramid of biomass can be inverted in aquatic ecosystems. Only pyramid of energy is always upright.

• **Mixing up primary and secondary pollutants** → Primary pollutants are directly emitted (SO₂, CO, NO). Secondary pollutants form by reactions in atmosphere (ozone at ground level, PAN, acid rain).

Quick Reference

• **Ecosystem = Biotic + Abiotic components interacting through energy flow and nutrient cycling**
• **Food chain energy rule: Only 10% transfers to the next level**
• **Producers → Herbivores → Carnivores → Top Carnivores → Decomposers (recycle at all levels)**
• **Air pollutants: CO, SO₂, NO₂, particulates, ozone; Water pollutants: sewage, heavy metals, pesticides**
• **Greenhouse effect gases: CO₂, CH₄, N₂O cause global warming**
• **Higher trophic level = less energy, fewer organisms, more toxin concentration (biomagnification)**