Quick Revision Notes: Class 10 Science

Chapter: Our Environment

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1. Introduction & Ecosystem

• Environment: Everything that surrounds us, including living (biotic) and non-living (abiotic) components.
• Ecosystem: A self-contained unit of living organisms (plants, animals, microorganisms) interacting with each other and with the non-living components (light, air, water, soil) of their environment.
  • Biotic Components: Living organisms like Producers, Consumers, and Decomposers.
  • Abiotic Components: Physical factors like temperature, rainfall, wind, soil, and minerals.
• Types of Ecosystems:
  • Natural Ecosystems: Forests, ponds, lakes, oceans.
  • Artificial (Man-made) Ecosystems: Crop fields, gardens, aquariums.

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2. Components of an Ecosystem

• Producers (Autotrophs): Organisms that make their own food using sunlight (e.g., green plants, blue-green algae).
• Consumers (Heterotrophs): Organisms that depend directly or indirectly on producers for food.
  • Herbivores: Plant-eaters (e.g., cow, deer, rabbit).
  • Carnivores: Flesh-eaters (e.g., lion, tiger, snake).
  • Omnivores: Eat both plants and animals (e.g., human, crow).
  • Parasites: Live on or inside a host and get food from it (e.g., ticks, lice, Cuscuta).
• Decomposers: Microorganisms (bacteria and fungi) that break down complex organic substances into simple inorganic substances from dead remains and waste products.
  • Role: They cleanse the environment and replenish nutrients in the soil.

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3. Food Chain, Food Web, and Trophic Levels

• Trophic Levels: The specific steps in a food chain where energy transfer takes place.

  • 1st Trophic Level: Producers (Autotrophs)
  • 2nd Trophic Level: Herbivores (Primary Consumers)
  • 3rd Trophic Level: Carnivores (Secondary Consumers)
  • 4th Trophic Level: Large Carnivores (Tertiary Consumers)

• Food Chain: A linear network of links in a food chain starting from producer organisms and ending at apex predator species.

  • Example: Grass $\rightarrow$ Grasshopper $\rightarrow$ Frog $\rightarrow$ Snake $\rightarrow$ Hawk

• Food Web: A natural interconnection of multiple food chains in an ecosystem. It represents multiple feeding relationships.

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4. Flow of Energy in an Ecosystem

• Key Points:
  • Energy flow is unidirectional (one-way): Sun $\rightarrow$ Producers $\rightarrow$ Herbivores $\rightarrow$ Carnivores.
  • Energy is not recycled.
  • Green plants capture about 1% of the sun's energy falling on their leaves and convert it into food energy.

Ten Percent Law (Lindeman's Law):

Only 10% of the energy is transferred to the next trophic level, while the remaining 90% is lost to the environment as heat during metabolic processes.

• Example Calculation:
  • If Producers have 1000 J of energy:
    • 1st Trophic Level (Producers) = 1000 J
    • 2nd Trophic Level (Herbivores) = 100 J (10% of 1000)
    • 3rd Trophic Level (Carnivores) = 10 J (10% of 100)
    • 4th Trophic Level (Top Carnivores) = 1 J (10% of 10)

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5. Biological Magnification (Biomagnification)

• Definition: The progressive accumulation of harmful non-biodegradable chemical substances (like pesticides, heavy metals, DDT) at each successive trophic level in a food chain.
• Key Fact: Since chemicals cannot be degraded, their concentration increases highest at the top trophic level (e.g., in humans or top birds).

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6. Environmental Problems

A. Depletion of Ozone Layer ($O_3$)

• Ozone Layer: Found in the stratosphere (higher reaches of the atmosphere). It shields the Earth's surface from harmful ultraviolet (UV) radiations from the sun.
• Formation of Ozone: UV rays split molecular oxygen ($O_2$) into free oxygen ($O$) atoms, which then combine with molecular oxygen to form ozone ($O_3$).
  • $O_2 \xrightarrow{\text{UV}} O + O$
  • $O + O_2 \rightarrow O_3$
• Depletion Cause: Excessive use of CFCs (Chlorofluorocarbons) used in refrigerators, fire extinguishers, and aerosols. CFCs destroy ozone molecules.
• Impact of UV Rays: Skin cancer, cataracts in eyes, damage to the immune system, and reduction in crop yields.

B. Waste Management

• Biodegradable Wastes: Substances that are broken down by biological processes (microorganisms).
  • Example: Peel of fruits and vegetables, paper, cow dung, leaves. (Eco-friendly, do not persist long).
• Non-Biodegradable Wastes: Substances that are not broken down by biological processes.
  • Example: Plastics, polythene bags, glass, DDT, synthetic fibers. (Persist in the environment for a long time and cause pollution).

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7. Eco-friendly Practices (How to Protect the Environment)

• The 3 R's:
  1. Reduce: Using less material (e.g., saving electricity, saving water, not wasting food).
  2. Reuse: Using things again and again instead of throwing them away (e.g., jam jars, envelopes).
  3. Recycle: Processing waste materials to make new things (e.g., recycling paper, plastic, glass).
• Sustainable Development: Using resources judiciously to meet the needs of the present generation while conserving them for future generations.