Class 10 Science Notes Chapter 15 (Chapter 15) – Examplar Problems (English) Book

Detailed Notes with MCQs of Chapter 15, 'Our Environment'. This is a crucial chapter, not just for your board exams but also forms the basis for environmental science questions in many government exams. We'll go through the key concepts systematically.

Chapter 15: Our Environment - Detailed Notes

1. Environment:

• Everything that surrounds us constitutes our environment.
• It includes living (biotic) and non-living (abiotic) components.
• These components interact with each other, forming complex systems.

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. They are categorized based on how they obtain nutrition:
    • Producers: Organisms that produce their own food using light energy (photosynthesis) or chemical energy. Examples: Green plants, blue-green algae (cyanobacteria). They form the base of most food chains.
    • Consumers: Organisms that depend directly or indirectly on producers for food.
      • Herbivores (Primary Consumers): Feed directly on producers (plants). Examples: Deer, rabbit, grasshopper.
      • Carnivores (Secondary/Tertiary Consumers): Feed on other animals.
        • Secondary Consumers: Feed on herbivores. Examples: Fox, frog, snake.
        • Tertiary Consumers: Feed on other carnivores. Examples: Lion, eagle, tiger.
      • Omnivores: Feed on both plants and animals. Examples: Humans, bears, crows.
      • Parasites: Live on or inside another organism (host) and derive nutrition from it. Examples: Cuscuta (Amarbel), ticks.
    • Decomposers: Organisms that break down the dead remains and waste products of other organisms. They return nutrients to the soil, air, and water, making them available again for producers. Examples: Bacteria, Fungi. They play a vital role in nutrient cycling.

• Types of Ecosystems:

  • Natural Ecosystems: Operate under natural conditions without major human interference.
    • Terrestrial: Forests, grasslands, deserts.
    • Aquatic: Ponds, lakes, rivers, oceans, estuaries.
  • Artificial (Man-made) Ecosystems: Created and maintained by humans. Examples: Crop fields, gardens, aquariums. These are often less diverse and require constant human management.

3. Food Chains and Food Webs:

• Food Chain: A sequence of organisms where each organism is eaten by the next organism in the chain, showing the flow of energy. Example: Grass → Grasshopper → Frog → Snake → Eagle.
• Trophic Levels: Each step or level in a food chain where transfer of energy occurs.
  • 1st Trophic Level: Producers (Plants)
  • 2nd Trophic Level: Primary Consumers (Herbivores)
  • 3rd Trophic Level: Secondary Consumers (Carnivores feeding on herbivores)
  • 4th Trophic Level: Tertiary Consumers (Carnivores feeding on other carnivores)
• Energy Flow:
  • Unidirectional: Energy flows from the sun to producers, then to consumers. It does not flow back.
  • 10% Law: Only about 10% of the energy entering a particular trophic level is available for transfer to the next higher trophic level. The rest is lost as heat during metabolic processes, used for growth, reproduction, etc. This limits the number of trophic levels in a food chain (usually 3-5).
• Food Web: A network of interconnected food chains existing in an ecosystem. It provides alternative pathways for energy flow and increases the stability of the ecosystem. If one population changes, others have alternative food sources.

4. Biological Magnification (Biomagnification):

• Definition: The increasing concentration of harmful, non-biodegradable chemical substances (like pesticides, heavy metals) in the bodies of organisms at successive higher trophic levels in a food chain.
• Example: DDT sprayed on crops enters the water, is absorbed by aquatic plants (producers), eaten by zooplankton (primary consumers), then small fish (secondary consumers), then large fish (tertiary consumers), and finally fish-eating birds (top consumers). The concentration of DDT increases significantly at each level, potentially causing harm, especially to top predators. Humans can also be affected by consuming contaminated food.

5. Environmental Problems:

• Ozone Layer Depletion:

  • Ozone (O₃): A molecule formed by three atoms of oxygen. Found primarily in the stratosphere.
  • Function: The ozone layer absorbs most of the harmful ultraviolet (UV) radiation from the sun, protecting life on Earth.
  • Formation: O₂ + UV → O + O ; O + O₂ → O₃
  • Depletion: Caused mainly by synthetic chemicals like Chlorofluorocarbons (CFCs), used in refrigerants, aerosols, etc.
    • CFCs release chlorine atoms in the stratosphere.
    • Chlorine acts as a catalyst, breaking down ozone molecules (O₃) into oxygen (O₂). One chlorine atom can destroy thousands of ozone molecules.
  • Effects of Depletion: Increased UV radiation reaching Earth can cause skin cancer, cataracts, damage to eyes, harm immune systems, and affect plant life and plankton.
  • Control: The Montreal Protocol (1987) is an international treaty aimed at phasing out the production and consumption of ozone-depleting substances like CFCs.

• Waste Management:

  • Waste (Garbage): Useless or discarded materials generated from human activities.
  • Types of Waste:
    • Biodegradable Waste: Wastes that can be broken down into simpler, harmless substances by the action of microorganisms (decomposers). Examples: Kitchen waste (vegetable peels, leftover food), paper, cotton, wood, sewage, cattle dung.
    • Non-biodegradable Waste: Wastes that cannot be broken down by microorganisms and persist in the environment for long periods, causing pollution. Examples: Plastics, glass, metals, synthetic fibres, pesticides, radioactive wastes.
  • Problems caused by Waste: Soil pollution, water pollution, air pollution (if burnt), spread of diseases, harm to wildlife. Non-biodegradable wastes clog drains and accumulate in landfills.
  • Methods of Waste Disposal:
    • Recycling: Processing waste materials to create new products (e.g., paper, glass, metals, some plastics).
    • Composting: Biological decomposition of organic biodegradable waste under controlled aerobic conditions to produce manure (compost). Vermicomposting uses earthworms.
    • Incineration: Burning waste at very high temperatures to reduce its volume. Can generate heat for energy but may cause air pollution if not done properly (requires pollution control devices). Best suited for medical/toxic waste.
    • Landfill: Disposal of waste in low-lying areas, compacted and covered with soil. Can cause soil and groundwater pollution (leachate) if not properly designed and managed.
    • Sewage Treatment: Processing wastewater from households and industries to remove pollutants before discharging it into water bodies.

Key Takeaways for Exams:

• Understand the definitions and roles of ecosystem components (producers, consumers, decomposers).
• Know the difference between food chains and food webs, and the concept of trophic levels.
• Remember the 10% law of energy transfer and its implications.
• Understand biological magnification and its causes (non-biodegradable substances).
• Know the importance of the ozone layer, the cause of its depletion (CFCs), and its consequences. Remember the Montreal Protocol.
• Differentiate between biodegradable and non-biodegradable waste with examples.
• Be familiar with various methods of waste disposal and their pros and cons.
• The role of decomposers is critical – they recycle nutrients and clean the environment.

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) Accumulation

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

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

6. Which group of organisms are not constituents of a food chain?
   a) Grass, lion, rabbit
   b) Plankton, man, fish, grasshopper
   c) Wolf, grass, snake, tiger
   d) Frog, snake, eagle, grass, grasshopper

7. Organisms which synthesise carbohydrates from inorganic compounds using radiant energy are called:
   a) Decomposers
   b) Producers
   c) Herbivores
   d) Carnivores

8. Which of the following is a non-biodegradable waste?
   a) Paper
   b) Vegetable peels
   c) Plastic bottles
   d) Cotton cloth

9. In the given food chain: Grass → Deer → Lion, if 10000 J of energy is available at the producer level (Grass), how much energy will be available to the Lion?
   a) 1000 J
   b) 100 J
   c) 10 J
   d) 1 J

10. The primary role of decomposers in an ecosystem is to:
    a) Trap solar energy
    b) Provide food for herbivores
    c) Break down organic matter and recycle nutrients
    d) Consume producers directly

Answer Key for MCQs:

1. b) Grass, Goat, Human
2. c) Chemical energy
3. c) Biomagnification
4. d) Humidity
5. c) Chlorofluorocarbons
6. b) Plankton, man, fish, grasshopper (Grasshopper doesn't fit logically after fish/man in a simple chain starting with plankton) Self-correction: Option (c) is better as Wolf, grass, snake, tiger doesn't form a linear chain. Let's re-evaluate. (b) could be part of a complex web, but not a single chain. (c) Wolf doesn't eat grass, snake doesn't eat grass. So (c) is definitely not a chain. Let's re-examine (b). Plankton -> Fish -> Man is a chain. Grasshopper is separate. So (b) contains organisms, some of which are not part of one specific linear chain shown. (c) contains organisms that cannot form a single linear food chain among themselves in that order or any simple order. Therefore, (c) is a better answer representing a group that doesn't constitute a food chain. Let's stick with (c). Final check: (c) Wolf, grass, snake, tiger. This group cannot form a single food chain. Wolf/Tiger eat animals, snake eats animals, grass is a producer. No linear sequence works.
7. b) Producers
8. c) Plastic bottles
9. b) 100 J (Grass: 10000 J -> Deer: 10% of 10000 = 1000 J -> Lion: 10% of 1000 = 100 J)
10. c) Break down organic matter and recycle nutrients

Make sure you understand the reasoning behind each answer, especially the energy flow calculation and the roles of different organisms. Study these notes well. Let me know if any part needs further clarification.