Our Environment

Why This Chapter Matters

Environment chapter has 4-6 marks in board exams and is also important for general awareness. Food chains, trophic levels, ozone depletion, and waste management are regularly tested. This chapter is also relevant for environmental awareness.

Prerequisites

Core Concepts

1. Ecosystem

Ecosystem: All the living organisms in an area and the non-living components of that area function together as a system.

Components:

Types: Natural (forest, pond, ocean) and Artificial (aquarium, garden, crop field)

2. Food Chain and Food Web

Food chain: Linear sequence showing flow of energy from producers to consumers.

Example: Grass → Grasshopper → Frog → Snake → Eagle

Food web: Multiple interconnected food chains.

More food webs = more stable ecosystem.

Producers: Green plants (autotrophs) — make own food through photosynthesis.

Consumers: Animals (heterotrophs)

Decomposers: Break down dead organisms (bacteria, fungi) — recycle nutrients.

3. Trophic Levels

Each feeding level in a food chain is a trophic level.

|---|---|---|

4. Flow of Energy — 10% Law

Energy transfer is inefficient. Only 10% of energy at one trophic level is available to the next level (90% is lost as heat, respiration, etc.).

1000 kJ (Producers) → 100 kJ (Primary consumers) → 10 kJ (Secondary) → 1 kJ (Tertiary)

Implications:

5. Biological Magnification

Concentration of harmful chemicals (pesticides like DDT) INCREASES as we go up the trophic levels.

Example:

Reason: Chemicals are not biodegradable — accumulate in fatty tissues. Each consumer eats many prey organisms, concentrating the chemical.

Effect: Top predators and humans most affected — reproductive failure in birds (thin eggshells), cancer risks.

6. Biodegradable and Non-biodegradable Waste

Biodegradable: Can be broken down by microorganisms (bacteria, fungi)

Examples: Food waste, paper, cotton cloth, leather, wood, vegetable peels, animal dung

Non-biodegradable: Cannot be broken down naturally (or takes very long)

Examples: Plastics, synthetic fibres (nylon, polyester), glass, metals, pesticides like DDT

Problems with non-biodegradable waste:

Waste management:

7. Ozone Layer

Ozone (O₃): Three oxygen atoms. Found in stratosphere (15-50 km above Earth).

Function: Absorbs harmful UV (ultraviolet) radiation from the Sun.

UV-B and UV-C cause: skin cancer, cataracts, suppression of immune system, damage to DNA.

Ozone depletion — CFCs:

Chlorofluorocarbons (CFCs) used in refrigerators, air conditioners, aerosol sprays rise to stratosphere.

UV radiation breaks CFCs → releases Cl atoms.

Cl + O₃ → ClO + O₂ → Cl regenerated → destroys more O₃ (chain reaction)

One Cl atom can destroy 100,000 O₃ molecules!

Ozone hole: Thinning of ozone layer, especially over Antarctica and Arctic.

Montreal Protocol (1987): International agreement to phase out CFCs.

CFC alternatives: HFCs (hydrochlorofluorocarbons) — less damaging.

The ozone layer is slowly recovering due to CFC phase-out.

PYQs

2023

Q: What is the 10% law of energy transfer? Give an example.

Only 10% of energy at one trophic level is available to the next level.

Example: If grass has 10,000 J → grasshopper gets 1,000 J → frog gets 100 J → snake gets 10 J.

90% lost at each level as heat, respiration, movement.

2022

Q: What is biological magnification? Why is it important?

Biological magnification = increasing concentration of harmful chemicals (like DDT) at higher trophic levels.

Important because top predators (including humans) are most affected, even if the chemical was at very low concentration originally.

2021

Q: Explain how ozone layer is depleted. What are the consequences?

CFCs (from refrigerators, AC) rise to stratosphere. UV breaks them → Cl atoms → Cl destroys O₃ (chain reaction).

Consequences: Increased UV radiation reaching Earth → skin cancer, cataracts, ecosystem damage.

2020

Q: Give two examples each of biodegradable and non-biodegradable substances.

Biodegradable: Food scraps, paper

Non-biodegradable: Plastic bags, DDT pesticide

MCQ Practice

Q1. Which of the following is NOT a decomposer?

(A) Bacteria (B) Fungi (C) Frog ✓ (D) Earthworm

Q2. In a food chain, energy available at each successive trophic level:

(A) Increases by 10% (B) Decreases by 10% (C) Increases by 90% (D) Decreases by 90% ✓

Q3 (Hard). If energy at T₁ = 10,000 kJ, what is energy available at T₄?

T₂ = 10,000 × 0.1 = 1,000 kJ

T₃ = 1,000 × 0.1 = 100 kJ

T₄ = 100 × 0.1 = 10 kJ (0.1% of original)

Revision Notes

ECOSYSTEM: Living + non-living components functioning together

FOOD CHAIN: Producers → Primary → Secondary → Tertiary consumers

10% LAW: Only 10% energy transferred to next level
  → Max 3-4 trophic levels practical

BIOLOGICAL MAGNIFICATION:
  Non-biodegradable chemicals INCREASE up the food chain
  DDT is classic example
  Top predators most affected

BIODEGRADABLE: paper, food, wood — broken down by decomposers
NON-BIODEGRADABLE: plastics, DDT, glass — persist in environment

OZONE LAYER (stratosphere):
  Absorbs UV-B and UV-C radiation
  CFCs destroy it (chain reaction via Cl atoms)
  Montreal Protocol (1987) — phase out CFCs
  
3R PRINCIPLE: Reduce → Reuse → Recycle

Common Mistakes:

❌ Ozone layer in troposphere — WRONG! It's in stratosphere (15-50 km altitude)

❌ Energy INCREASES up food chain — WRONG! Decreases (10% law)

❌ Biological magnification affects all levels equally — WRONG! Highest concentration at TOP

Related Topics