Class 10 Science Notes Chapter 18 (Chapter 18) – Examplar Problems (English) Book

Detailed Notes with MCQs of Chapter 18 from your NCERT Exemplar. Assuming this corresponds to the crucial topic of 'Our Environment' (which is Chapter 15 in the standard textbook but numbering can vary), this is a vital area for many government exams. Pay close attention as we break down the key concepts.

Chapter Notes: Our Environment (Based on NCERT Class 10 Science)

1. Environment:

• Definition: Everything that surrounds us, including living (biotic) and non-living (abiotic) components. It encompasses physical, chemical, and biological factors.
• Interaction between these components maintains a balance in nature.

2. Ecosystem:

• Definition: A functional unit of nature where living organisms interact among themselves and also with the surrounding physical environment.
• Components:
  • Abiotic Components: Non-living factors like air, water, soil, temperature, sunlight, humidity, wind, rainfall, inorganic nutrients (nitrogen, phosphorus, etc.).
  • Biotic Components: Living organisms. Classified based on nutrition:
    • Producers: Organisms that produce their own food using light energy (photosynthesis) or chemical energy. Primarily green plants and certain blue-green algae (cyanobacteria). They form the base of the ecosystem.
    • 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, snake).
      • Carnivores (Tertiary Consumers): Feed on other carnivores (e.g., eagle, lion, tiger).
      • Omnivores: Feed on both plants and animals (e.g., humans, crow, bear).
    • Decomposers: Microorganisms (mainly bacteria and fungi) that break down dead organic matter (dead plants, animals, waste products) into simpler inorganic substances. They play a crucial role in nutrient recycling.

3. Food Chain:

• Definition: A sequence of organisms where each organism is eaten by the next organism in the chain, representing the flow of energy.
• Structure: Producer → Primary Consumer → Secondary Consumer → Tertiary Consumer
• Examples:
  • Grass → Grasshopper → Frog → Snake → Eagle (Terrestrial)
  • Phytoplankton → Zooplankton → Small Fish → Large Fish (Aquatic)
• 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/Omnivores)
  • 4th Trophic Level: Tertiary Consumers (Top Carnivores/Omnivores)

4. Food Web:

• Definition: A network of interconnected food chains operating in an ecosystem. It provides alternative pathways for energy flow and increases ecosystem stability.
• An organism can occupy different trophic levels in different food chains within the same food web.

5. Energy Flow in Ecosystems:

• Unidirectional: Energy flows from the sun to producers, then to consumers, and is not recycled back.
• 10% Law (Proposed by Lindeman): 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), growth, reproduction, or remains uneaten/undigested.
• This limits the number of trophic levels in a food chain (usually 3-5).

6. Biological Magnification (Biomagnification):

• Definition: The increasing concentration of certain harmful, non-biodegradable chemicals (like pesticides, heavy metals) at successive trophic levels in a food chain.
• Top-level consumers accumulate the highest concentration of these toxins, which can cause significant harm. Example: DDT accumulation.

7. Environmental Problems:

• Ozone Layer Depletion:

  • Ozone (O₃): A molecule formed by three atoms of oxygen. Found predominantly in the stratosphere.
  • Function: Acts as a shield, absorbing most of the harmful ultraviolet (UV) radiation from the sun.
  • Depletion: Thinning of the ozone layer, primarily caused by synthetic chemicals like Chlorofluorocarbons (CFCs) used in refrigerants, aerosols, etc.
  • Mechanism: CFCs release chlorine atoms in the stratosphere, which catalytically destroy ozone molecules. One chlorine atom can destroy thousands of ozone molecules.
  • Consequences: Increased UV radiation reaching Earth leads to skin cancer, cataracts, damage to immune systems, and harm to plants and plankton.
  • Mitigation: International agreements like the Montreal Protocol aim to phase out ozone-depleting substances (ODS).

• Waste Management:

  • Waste (Garbage): Unwanted or unusable materials. Includes household waste, industrial waste, agricultural waste, etc.
  • Types of Waste based on Degradability:
    • Biodegradable Waste: Waste 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 that cannot be broken down by microorganisms into simpler substances. They persist in the environment for long periods, causing pollution. Examples: Plastics, glass, metals, synthetic fibres, pesticides, radioactive waste.
  • Problems with Non-biodegradable Waste: Land pollution, water pollution, soil degradation, harm to wildlife, blockage of drains. Accumulation leads to biomagnification if toxic.
  • Waste Disposal Methods:
    • Landfills: Burying waste in low-lying areas, compacted and covered with soil.
    • Incineration: Burning waste at high temperatures to reduce volume (can cause air pollution if not controlled).
    • Composting: Converting biodegradable waste into manure.
    • Recycling: Processing waste materials to create new products (e.g., paper, plastic, glass, metal).
    • Reuse: Using items again for their original purpose or a new purpose.
  • The 3 R's (or 5 R's): Reduce, Reuse, Recycle (Refuse, Repurpose are often added). A strategy for sustainable waste management.

Multiple Choice Questions (MCQs) for Practice:

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

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

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

7. In the given food chain: Grass → Deer → Lion, if 1000 J of energy is available at the producer level (Grass), how much energy will be available to the Lion?
   (a) 100 J
   (b) 10 J
   (c) 1 J
   (d) 0.1 J

8. Which of the following is NOT a biodegradable waste?
   (a) Vegetable peels
   (b) Cotton cloth
   (c) Polythene bags
   (d) Waste paper

9. The primary role of decomposers in an ecosystem is:
   (a) To produce food using sunlight
   (b) To consume producers directly
   (c) To recycle nutrients from dead organic matter
   (d) To form the highest trophic level

10. A network of interconnected food chains is called a:
    (a) Trophic level
    (b) Food web
    (c) Ecological pyramid
    (d) Ecosystem cycle

Answer Key for MCQs:

1. (b)
2. (b)
3. (c)
4. (d)
5. (b)
6. (c)
7. (b) [Grass (1000 J) -> Deer (10% of 1000 J = 100 J) -> Lion (10% of 100 J = 10 J)]
8. (c)
9. (c)
10. (b)

Study these notes thoroughly. Understanding the interactions within our environment and the impact of human activities is crucial, not just for exams but for responsible citizenship. Let me know if any specific point needs further clarification.