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Our Environment – Class 10 Science Chapter 13 Notes & NCERT PDF

Class 10ScienceChapter 13NCERT book: Science - Class 10

Notes and a simple summary of Chapter 13 of the NCERT Class 10 Science book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 13: Our Environment

Introduction

We often hear that the "environment" is not what it used to be and that global summits discuss "environmental" issues. This chapter studies how the components of the environment interact with each other and how human activities affect the environment, focusing on two problems: ozone depletion and waste disposal.

Key Concepts

1. Ecosystem and its components

  • All the interacting organisms in an area together with the non-living constituents form an ecosystem.
  • Biotic components: living organisms. Abiotic components: physical factors such as temperature, rainfall, wind, soil and minerals.
  • Natural ecosystems: forests, ponds, lakes. Human-made (artificial): gardens, crop-fields, an aquarium (Activity 13.1).
  • Producers: green plants and certain bacteria that make food by photosynthesis using sunlight and chlorophyll.
  • Consumers: depend on producers directly or indirectly — herbivores, carnivores, omnivores and parasites.
  • Decomposers: bacteria and fungi that break down dead remains and wastes into simple inorganic substances that return to the soil for plants — they replenish the soil.

    • 2. Food chains and trophic levels

  • A series of organisms feeding on one another is a food chain; each step is a trophic level.

    • - 1st: producers (autotrophs)

    - 2nd: herbivores (primary consumers)

    - 3rd: small carnivores (secondary consumers)

    - 4th: large carnivores (tertiary consumers)

  • Examples from the book: food chains in a forest, grassland and pond, e.g. grass → deer → lion.

    • 3. Flow of energy — the 10% law

  • Green plants in a terrestrial ecosystem capture about 1% of the sunlight falling on their leaves.
  • A great deal of energy is lost as heat at each step. On average, only 10% of the food eaten is turned into the organism's body and made available to the next level.
    • Ten per cent law: about 10% of the energy/organic matter at one trophic level reaches the next.
  • So food chains usually have only three or four steps; there are more individuals at lower levels, the greatest number being producers.
  • Energy flow is unidirectional — it never returns to the Sun or to a previous level — and diminishes progressively at each level.
  • Branching, interlinked food chains form a food web.

    • 4. Biological magnification

  • Pesticides and other chemicals used on crops wash into soil and water, are absorbed by plants and aquatic organisms, and enter the food chain.
  • Being non-degradable, they accumulate progressively at each trophic level. Humans, at the top, get the maximum concentration — this is biological magnification. That is why grains, vegetables, fruits and meat carry pesticide residues that washing cannot always remove.

    • 5. Ozone layer and its depletion

  • Ozone (O₃) has three oxygen atoms. At ground level it is a deadly poison, but in the upper atmosphere it shields the Earth from harmful UV radiation, which can cause skin cancer.
  • Formation:
    • O₂ —(UV)→ O + O · O + O₂ → O₃ (ozone)
  • Ozone began to drop sharply in the 1980s, linked to chlorofluorocarbons (CFCs) used as refrigerants and in fire extinguishers.
  • In 1987 the United Nations Environment Programme (UNEP) forged an agreement to freeze CFC production at 1986 levels. Manufacturers must now make CFC-free refrigerators.

    • 6. Managing the garbage we produce

  • Biodegradable substances are broken down by biological processes (bacteria, other saprophytes) — e.g., vegetable peels, paper, cotton.
  • Non-biodegradable substances are not broken down by biological processes — e.g., plastics, some chemicals; they persist and harm ecosystems.
  • Enzymes are specific in action, which is why some substances cannot be broken down.
  • Changes in lifestyle have increased waste and packaging; use of disposable items adds to garbage. Waste should be segregated and disposed of responsibly.

    • Board Exam Focus

  • Define ecosystem; list biotic/abiotic components; role of decomposers.
  • Trophic levels with an example food chain; why food chains have only 3–4 steps.
  • 10% law numericals (e.g., 10 000 J at producers → 1000 J → 100 J → 10 J).
  • Biological magnification, ozone formation and depletion, CFCs and the 1987 UNEP agreement.
  • Biodegradable vs non-biodegradable with examples.

    • Quick Fact Sheet

  • ~1% of sunlight is captured by plants; ~10% passes to each next level.
  • Trophic levels: producer → herbivore → small carnivore → large carnivore.
  • Ozone: O₃; formed by UV splitting O₂; depleted by CFCs; UNEP agreement 1987.

    • Key Terms

  • Ecosystem (पारितंत्र) — organisms plus their non-living surroundings
  • Biotic / Abiotic (जैव / अजैव) — living / non-living components
  • Producers (उत्पादक) — photosynthetic organisms
  • Consumers (उपभोक्ता) — organisms that eat other organisms
  • Decomposers (अपघटक) — bacteria and fungi that break down remains
  • Food chain (आहार श्रृंखला) — sequence of who eats whom
  • Trophic level (पोषी स्तर) — each step of a food chain
  • Food web (आहार जाल) — interconnected food chains
  • Ten per cent law (दस प्रतिशत नियम) — 10% energy transfer
  • Biological magnification (जैव आवर्धन) — chemicals concentrating up the chain
  • Ozone layer (ओज़ोन परत) — UV shield in the upper atmosphere
  • CFCs (क्लोरोफ्लोरो कार्बन) — ozone-depleting chemicals
  • Biodegradable (जैव निम्नीकरणीय) — broken down by biological processes
  • Non-biodegradable (अजैव निम्नीकरणीय) — not broken down biologically

    • Common Mistakes

  • Saying energy flows in a cycle — it is unidirectional; only nutrients cycle.
  • Thinking ozone is good everywhere — at ground level it is poisonous.
  • Confusing the 1% (sunlight captured) with the 10% (passed to the next level).
  • Listing paper or peels as non-biodegradable, or plastics as biodegradable.
  • Forgetting decomposers when describing an ecosystem — without them the soil would not be replenished.

    • 💡 Key Learning Points

    • ✓Define an ecosystem and distinguish biotic and abiotic components, natural and artificial ecosystems
    • ✓Identify producers, consumers and decomposers, and arrange organisms into trophic levels
    • ✓Apply the 10% law and explain why energy flow is unidirectional and food chains are short
    • ✓Explain biological magnification and the formation and depletion of the ozone layer
    • ✓Classify wastes as biodegradable or non-biodegradable and suggest responsible disposal

    👨‍🏫 Teaching Tips

    • →Set up a classroom aquarium (Activity 13.1) and discuss why it still needs cleaning
    • →Have groups build food chains of three or more steps from pond organisms (Activity 13.2)
    • →Use a pyramid of blocks to show 10% energy transfer from 10 000 J down to 10 J
    • →Hold the newspaper debate on pesticide bans suggested in Activity 13.3
    • →Show the O₂ → O + O → O₃ reaction and link CFC use to refrigerators at home
    • →Run a one-day waste audit where students sort their school waste into biodegradable and non-biodegradable
    • →Connect biological magnification to the food students eat and ways to reduce pesticide intake

    📋 Assessment Questions

    1. Can the student name the trophic levels in a given food chain?
    2. Can the student calculate energy available at higher trophic levels using the 10% law?
    3. Can the student explain biological magnification and why humans are most affected?
    4. Can the student write how ozone is formed and what depletes it?
    5. Can the student classify given wastes as biodegradable or non-biodegradable?

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    Keep learning

    All chapters in Science - Class 10

    1. 1. Chemical Reactions and Equations
    2. 2. Acids, Bases and Salts
    3. 3. Metals and Non-metals
    4. 4. Carbon and its Compounds
    5. 5. Life Processes
    6. 6. Control and Coordination
    7. 7. How do Organisms Reproduce?
    8. 8. Heredity
    9. 9. Light – Reflection and Refraction
    10. 10. The Human Eye and the Colourful World
    11. 11. Electricity
    12. 12. Magnetic Effects of Electric Current
    13. 13. Our Environment