Class 10 Science - Chapter 15:
Our Environment
Chapter 15 of NCERT Class 10 Science discusses the interdependence of organisms and their surroundings, emphasizing the need for a sustainable environment. Here's a summary of the lesson and a list of important questions with their answers.
Summary of Each Section
1. Ecosystem and Its Components
Definition: An ecosystem comprises all living organisms (biotic components) and their physical surroundings (abiotic components) interacting with each other.
Types: Natural (forests, ponds) and Artificial (gardens, aquariums).
Key Interactions: Producers (plants), consumers (animals), and decomposers (fungi, bacteria).
2. Food Chains and Food Webs
Food Chain: A sequence showing energy flow from producers to top consumers.
Example: Grass → Grasshopper → Frog → Snake → Eagle.
Food Web: Interconnected food chains in an ecosystem.
Trophic Levels: Levels in a food chain where organisms obtain energy.
3. Biodegradable and Non-Biodegradable Wastes
Biodegradable Waste: Decomposes naturally (vegetable peels, paper).
Non-Biodegradable Waste: Does not decompose easily (plastic, metals).
4. Ozone Layer and Its Depletion
The ozone layer is a protective shield in the Earth’s stratosphere that absorbs the majority of the Sun’s harmful ultraviolet (UV) radiation, particularly UV-B and UV-C rays. This layer is crucial for life on Earth as it prevents excessive UV radiation, which can cause skin cancer, cataracts, and harm to plants and animals.
Structure and Function of Ozone
Ozone (O₃) is a molecule composed of three oxygen atoms. It forms when ultraviolet light splits an oxygen molecule (O₂) into individual oxygen atoms, which then combine with other O₂ molecules to form O₃. The ozone layer is most concentrated between 15 and 35 kilometers above Earth’s surface.
Causes of Ozone Depletion
1. Chlorofluorocarbons (CFCs):
Found in refrigerants, aerosol sprays, and solvents. CFCs release chlorine atoms when broken down by UV light. These chlorine atoms destroy ozone molecules in a catalytic reaction.
2. Halons and Other Ozone-Depleting Substances (ODS):
Used in fire extinguishers, they release bromine atoms that are even more destructive than chlorine.
3. Nitrous Oxides (Nâ‚‚O):
Emitted from fertilizers, industrial processes, and vehicle exhausts, they contribute to ozone destruction.
4. Natural Causes:
Volcanic eruptions and solar cycles can influence ozone levels, but human activities are the primary cause of depletion.
Effects of Ozone Depletion
Health Risks: Increased exposure to UV radiation leads to skin cancer, cataracts, and weakened immune systems.
Environmental Impact: Damage to crops, reduced productivity in phytoplankton (essential to the marine food chain), and harm to animals.
Climate Change: Though distinct from global warming, ozone depletion interacts with climate systems, affecting temperature and weather patterns.
Efforts to Protect the Ozone Layer
Montreal Protocol (1987):
A global treaty to phase out ODS like CFCs. It has been highly effective, with most countries complying.
Alternative Technologies:
Adoption of ozone-friendly substitutes in refrigeration, air conditioning, and other industries.
Raising Awareness:
Educating people on reducing the use of products containing ODS.
Current Status
The ozone layer is gradually recovering due to global efforts. However, it will take decades for the ozone layer to return to pre-1980 levels completely, highlighting the importance of sustained global cooperation and action.
5. Managing the Environment
Reduce, Reuse, Recycle: Strategies for sustainable living. Ban on Plastics: Plastic takes centuries to decompose, causing environmental hazards.
Conservation: Emphasis on conserving resources and reducing pollution.
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Important Questions and Answers Of the lesson Our Environment Class 10 Chapter 15
Q. What is an ecosystem? Give an example.
Answer: An ecosystem is a community of living organisms interacting with each other and their non-living environment. Example: A pond.
Q. What are decomposers? Why are they important in an ecosystem?
Answer: Decomposers break down dead plants and animals into simpler substances. They recycle nutrients and help in maintaining ecosystem balance.
Q. Define biodegradable and non-biodegradable substances. Give examples.
Answer: Biodegradable substances decompose naturally. Example: Paper, vegetable waste.
Non-biodegradable substances do not decompose easily. Example: Plastic, glass.
Q. What is a trophic level? Give an example.
Answer: A trophic level represents a step in the food chain.
Example: In Grass → Goat → Lion, grass is the first trophic level.
Q. What is an ecosystem? Give an example.
Answer: An ecosystem is a community of living organisms (plants, animals, and microorganisms) interacting with each other and their non-living surroundings (soil, water, air) in a specific area.
Example: A pond ecosystem.
Q. What is the role of decomposers in the ecosystem?
Answer: Decomposers, like fungi and bacteria, break down dead organisms and organic waste into simpler substances. They recycle nutrients into the soil, making them available for plants and maintaining ecological balance.
Q. Differentiate between biodegradable and non-biodegradable substances.
Answer: Biodegradable substances: Decompose naturally by microorganisms. Example: Vegetable waste, paper.
Non-biodegradable substances: Do not decompose easily and persist in the environment. Example: Plastics, glass.
Q. What is a food chain? Provide an example.
Answer: A food chain is a sequence of organisms in which each organism eats the previous one and is eaten by the next.
Example: Grass → Grasshopper → Frog → Snake → Eagle.
Q. Why is the ozone layer important for life on Earth?
Answer: The ozone layer absorbs harmful ultraviolet (UV) radiation from the Sun, preventing it from reaching the Earth's surface. Without the ozone layer, UV radiation could cause skin cancer, cataracts, and harm to plants and animals.
Q. What are trophic levels? Explain with an example.
Answer: Trophic levels are the different levels in a food chain where organisms obtain their energy.
∆ First trophic level: Producers (plants).
∆ Second trophic level: Primary consumers (herbivores like deer).
∆ Third trophic level: Secondary consumers (carnivores like frogs).
∆ Fourth trophic level: Tertiary consumers (top carnivores like lions).
Example: Grass → Deer → Tiger.
Here, grass is the first trophic level, deer is the second, and the tiger is the third.
Q. What are the effects of adding non-biodegradable substances to the environment?
Answer: Non-biodegradable substances, like plastics, cause:
✓ Pollution of soil and water.
✓ Harm to aquatic and terrestrial animals if ingested.
✓ Blockage of drains, leading to waterlogging.
✓ Accumulation of toxic substances in the food chain (biomagnification).
Q. Explain the concept of biomagnification with an example.
Answer: Biomagnification is the process by which the concentration of harmful substances (like pesticides or heavy metals) increases at each successive trophic level in a food chain.
Example: In a food chain (Plankton → Small Fish → Large Fish → Bird), pesticides like DDT used in agriculture accumulate in plankton. These pesticides become more concentrated as they move up the food chain, causing harm to top consumers like birds.
Q. What steps can be taken to manage garbage effectively?
Answer:
✓ Segregation of waste: Separate biodegradable and non-biodegradable waste.
✓ Composting: Use biodegradable waste to make compost.
✓ Recycling: Reuse materials like plastic, paper, and glass.
✓ Ban on single-use plastics: Reduce non-biodegradable waste.
✓ Awareness campaigns: Educate people on proper waste disposal.
Q. How does the depletion of the ozone layer affect living organisms?
Answer: Increases UV radiation exposure, leading to:
i) Skin cancer and cataracts in humans.
ii) Reduced crop yield and damage to aquatic ecosystems.
iii) Affects the immune systems of living organisms.
Q. Why should we reduce the use of plastics?
Answer: Plastics are non-biodegradable and cause severe environmental damage. They pollute soil and water, harm wildlife, and take hundreds of years to decompose.
Q. How can students contribute to saving the environment?
Answer:
Practice the 3 Rs: Reduce, Reuse, Recycle.
a) Avoid using plastic bags.
b) Spread awareness about environmental conservation.
c) Participate in tree plantation drives.
Q. What are the effects of adding non-biodegradable waste to the environment?
Answer: Non-biodegradable waste causes:
a) Soil and water pollution.
b) Harm to wildlife.
c) Blockage of drains and increased flooding.
Q. Explain the concept of a food web with an example.
Answer: A food web is a network of interconnected food chains. Example: In a forest, a rabbit may eat grass, and a snake may eat the rabbit, while eagles may eat both rabbits and snakes.
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