Class 10 Science Notes Chapter 15 (Our environment) – Science Book

Detailed Notes with MCQs of Chapter 15, 'Our Environment'. This is a crucial chapter, not just for your board exams but also frequently tested in various government exams due to its relevance to general awareness and environmental science. Pay close attention to the definitions and processes we discuss.

Chapter 15: Our Environment - Detailed Notes for Exam Preparation

1. Environment:

• Everything that surrounds us constitutes our environment.
• It includes both living (biotic) and non-living (abiotic) components.
• These components interact with each other and maintain a balance in nature.

2. Ecosystem:

• Definition: An ecosystem is a self-sustaining functional unit consisting of all interacting organisms (biotic community) in an area and their interactions with the physical environment (abiotic components).
• Components:
  • Abiotic Components: Non-living factors like temperature, rainfall, wind, soil, minerals, sunlight, water, atmospheric gases.
  • Biotic Components: Living organisms.
    • Producers: Organisms that produce their own food using light energy (photosynthesis) or chemical energy. Primarily green plants and certain blue-green algae. They form the base of the food chain.
    • Consumers: Organisms that depend directly or indirectly on producers for food.
      • Herbivores (Primary Consumers): Feed directly on producers (e.g., deer, rabbit, grasshopper).
      • Carnivores (Secondary Consumers): Feed on herbivores (e.g., frog, fox, small birds).
      • Top Carnivores (Tertiary Consumers): Feed on other carnivores (e.g., lion, tiger, eagle).
      • Omnivores: Feed on both plants and animals (e.g., humans, crow, bear).
    • Decomposers: Microorganisms like bacteria and fungi that break down dead organic matter (dead plants, animals, waste products) into simpler inorganic substances. They play a vital role in nutrient recycling.
• Types of Ecosystems:
  • Natural Ecosystems: Operate under natural conditions without major human interference (e.g., forests, grasslands, deserts, ponds, lakes, oceans).
  • Artificial (Man-made) Ecosystems: Created and maintained by humans (e.g., crop fields, gardens, aquariums). These are often simpler and less stable than natural ecosystems.

3. Food Chains and Food Webs:

• Food Chain: A sequence of organisms where each organism is eaten by the next organism in the chain, representing the flow of energy.
  • Example: Grass → Grasshopper → Frog → Snake → Eagle
• Trophic Levels: Each step or level in a food chain where energy transfer occurs.
  • 1st Trophic Level: Producers (Plants)
  • 2nd Trophic Level: Primary Consumers (Herbivores)
  • 3rd Trophic Level: Secondary Consumers (Carnivores)
  • 4th Trophic Level: Tertiary Consumers (Top Carnivores)
• Energy Flow:
  • Energy flows unidirectionally from the sun to producers, then to consumers.
  • 10% Law: Only about 10% of the energy available at one trophic level is transferred to the next trophic level. The remaining 90% is lost as heat during metabolic processes (respiration, digestion, etc.) or remains unconsumed.
  • This limits the number of trophic levels in a food chain (usually 3-5).
• Food Web: A network of interconnected food chains operating in an ecosystem. It provides alternative pathways for food and represents a more realistic picture of energy flow. A food web increases the stability of an ecosystem.
• Biological Magnification (Biomagnification): The increasing concentration of harmful, non-biodegradable chemical substances (like pesticides, heavy metals) in the bodies of organisms at successive trophic levels in a food chain. The concentration is highest at the top trophic level. Example: DDT accumulation.

4. Human Impact on the Environment:

• a) Ozone Layer Depletion:

  • Ozone (O₃): A molecule formed by three atoms of oxygen.
  • Location: Primarily found in the Stratosphere layer of the atmosphere.
  • Function: The ozone layer acts as a protective shield, absorbing most of the harmful ultraviolet (UV) radiation from the sun, preventing it from reaching the Earth's surface.
  • Depletion: Thinning of the ozone layer.
  • Cause: Release of synthetic chemicals, mainly Chlorofluorocarbons (CFCs), used in refrigerants, aerosols, and fire extinguishers. CFCs release chlorine atoms in the stratosphere, which catalytically destroy ozone molecules.
  • Consequences: Increased UV radiation reaching Earth, leading to skin cancer, cataracts, damage to immune systems in humans, harm to plants and plankton.
  • Mitigation: International agreements like the Montreal Protocol (1987) aimed to phase out the production and use of ozone-depleting substances like CFCs.

• b) Waste Management:

  • Waste (Garbage): Useless, unwanted, or discarded materials generated from human activities.
  • Types of Waste:
    • Biodegradable Waste: Waste materials that can be broken down into simpler, harmless substances by the action of microorganisms (decomposers). Examples: Vegetable peels, fruit waste, paper, cotton, cow dung, sewage.
    • Non-biodegradable Waste: Waste materials that cannot be broken down by microorganisms and persist in the environment for a long time, causing pollution. Examples: Plastics, glass, polythene bags, synthetic fibers, metals, pesticides (like DDT).
  • Problems Caused by Waste: Soil pollution, water pollution, air pollution (if burnt), spread of diseases, harm to wildlife. Non-biodegradable waste accumulation is a major issue.
  • Methods of Waste Disposal:
    • Recycling: Processing waste materials to create new products (e.g., recycling paper, plastics, glass, metals).
    • Composting: Converting biodegradable organic waste into manure through decomposition (e.g., kitchen waste, garden waste). Vermicomposting uses earthworms.
    • Incineration: Burning waste at very high temperatures to reduce its volume. Often used for biomedical waste. Can cause air pollution if not done properly. Ash produced needs disposal.
    • Landfills: Disposing of waste in low-lying areas and covering it with soil. Can cause soil and groundwater pollution if not managed scientifically.
    • Sewage Treatment Plants (STPs): Treating wastewater from homes and industries before releasing it into water bodies.
  • Reducing Waste Generation: The best approach is to minimize waste production.
    • The 3 R's: Reduce, Reuse, Recycle.
      • Reduce: Use less (e.g., avoid single-use plastics).
      • Reuse: Use items again (e.g., carry cloth bags, reuse jars).
      • Recycle: Process waste to make new items.
    • Using disposable paper cups vs. plastic cups in trains/stalls. Kulhads (clay cups) are a more eco-friendly, biodegradable option.

Key Takeaways for Exams:

• Know the definitions: Ecosystem, Biotic/Abiotic components, Producers, Consumers, Decomposers, Food Chain, Food Web, Trophic Levels, Biodegradable/Non-biodegradable waste, Ozone, Biomagnification.
• Understand the processes: Energy flow (10% law), Nutrient cycling (role of decomposers), Ozone depletion (causes, effects), Waste disposal methods.
• Remember key examples and facts: Examples of different trophic levels, components of ecosystems, causes of ozone depletion (CFCs), Montreal Protocol, DDT as an example for biomagnification.

Multiple Choice Questions (MCQs)

1. Which of the following constitutes a food chain?
   a) Grass, Wheat, Mango
   b) Grass, Goat, Human
   c) Goat, Cow, Elephant
   d) Grass, Fish, Goat

2. In an ecosystem, the 10% energy available for transfer from one trophic level to the next is in the form of:
   a) Heat energy
   b) Light energy
   c) Chemical energy
   d) Mechanical energy

3. Accumulation of non-biodegradable pesticides in the food chain in increasing amounts at each higher trophic level is known as:
   a) Eutrophication
   b) Pollution
   c) Biomagnification
   d) Decomposition

4. Which of the following is an abiotic component of an ecosystem?
   a) Bacteria
   b) Plants
   c) Fungi
   d) Sunlight

5. Depletion of the ozone layer is mainly due to:
   a) Carbon dioxide
   b) Methane gas
   c) Chlorofluorocarbons (CFCs)
   d) Sulphur dioxide

6. Which of the following groups contains only biodegradable items?
   a) Grass, Flowers, Leather
   b) Grass, Wood, Plastic
   c) Fruit peels, Cake, Lime-juice
   d) Cake, Wood, Glass

7. In a food chain, the third trophic level is always occupied by:
   a) Carnivores
   b) Herbivores
   c) Decomposers
   d) Producers

8. An ecosystem includes:
   a) All living organisms
   b) Non-living objects
   c) Both living organisms and non-living objects
   d) Sometimes living organisms and sometimes non-living objects

9. The primary function of the ozone layer is to absorb:
   a) Infrared radiation
   b) Ultraviolet radiation
   c) Visible light
   d) Gamma rays

10. Which of the following is an example of an artificial ecosystem?
    a) Pond
    b) Forest
    c) Aquarium
    d) Lake

Answer Key for MCQs:

1. b) Grass, Goat, Human
2. c) Chemical energy (stored in the biomass)
3. c) Biomagnification
4. d) Sunlight
5. c) Chlorofluorocarbons (CFCs)
6. a) Grass, Flowers, Leather (Plastic, Glass are non-biodegradable) / c) Fruit peels, Cake, Lime-juice (Both a and c fit, but c is more consistently biodegradable kitchen/food waste) - Let's refine this. Leather tanning can involve non-biodegradable chemicals. Fruit peels, cake, and lime juice are clearly biodegradable. So (c) is a better answer.
7. a) Carnivores (Secondary consumers feeding on herbivores)
8. c) Both living organisms and non-living objects
9. b) Ultraviolet radiation
10. c) Aquarium

Revise these notes thoroughly. Understanding the concepts and remembering the key terms is essential for scoring well. Good luck with your preparation!