Our Environment – Class 10 Science Chapter 13 NCERT Notes
Class 10 Our Environment notes covering ecosystems, food chains, food webs, ozone depletion, and waste management for CBSE & ICSE boards.
Chapter 13: Our Environment
13.1 Ecosystem
An ecosystem is a self-sustaining system where living organisms (biotic components) interact with each other and with non-living components (abiotic components) in a particular area.
Components of an Ecosystem
- Abiotic (Non-living): Temperature, rainfall, wind, soil, sunlight, water, minerals.
- Biotic (Living):
- Producers (Autotrophs): Green plants and algae that make food by photosynthesis.
- Consumers (Heterotrophs): Organisms that depend on producers directly or indirectly for food.
- Primary consumers (Herbivores): eat producers. E.g., deer, grasshopper.
- Secondary consumers (Small carnivores): eat herbivores. E.g., frog, snake.
- Tertiary consumers (Top carnivores): eat secondary consumers. E.g., hawk, lion.
- Decomposers: Bacteria and fungi that break down dead organic matter, releasing nutrients back into the soil.
13.2 Food Chain and Food Web
A food chain is a series of organisms where each is eaten by the next member. Energy flows from one trophic level to the next.
Grass → Grasshopper → Frog → Snake → Hawk
(Producer → Primary Consumer → Secondary Consumer → Tertiary Consumer → Top Consumer)
A food web is an interconnected network of multiple food chains in an ecosystem. Food webs are more realistic than single food chains because most organisms eat and are eaten by multiple species.
Trophic Levels
Each step in a food chain is called a trophic level:
- T1: Producers (plants)
- T2: Primary consumers (herbivores)
- T3: Secondary consumers (small carnivores)
- T4: Tertiary consumers (top carnivores)
Only about 10% of the energy at each trophic level is transferred to the next level. The remaining 90% is used for life processes (respiration, digestion, movement) and lost as heat.
This is why food chains rarely have more than 3-4 trophic levels — there isn't enough energy to sustain more levels.
13.3 Biological Magnification
When harmful non-biodegradable chemicals (like pesticides — DDT, mercury) enter a food chain, their concentration increases at each successive trophic level. This phenomenon is called biological magnification or biomagnification.
Example: If DDT is sprayed on crops, producers absorb a small amount. Herbivores eating many plants accumulate more DDT. Carnivores eating many herbivores accumulate even higher concentrations. Top predators (like hawks) end up with the highest concentration, which can cause reproductive failure and death.
13.4 Ozone Layer and Its Depletion
Ozone (O₃) is a molecule consisting of three oxygen atoms. The ozone layer exists in the upper atmosphere (stratosphere) and shields life on Earth from harmful ultraviolet (UV) radiation from the Sun.
How Ozone is Formed and Destroyed
This is a dynamic equilibrium — ozone is constantly formed and broken down.
Cause of Ozone Depletion
Synthetic chemicals called chlorofluorocarbons (CFCs), used in refrigerators, air conditioners, and aerosol sprays, are the main cause. CFCs release chlorine atoms in the stratosphere, which catalytically destroy ozone molecules.
13.5 Waste Management
Biodegradable vs Non-biodegradable Waste
| Biodegradable | Non-biodegradable |
|---|---|
| Can be broken down by microorganisms | Cannot be broken down by biological processes |
| Examples: food waste, paper, cotton, cow dung | Examples: plastics, glass, metals, DDT, radioactive waste |
| Eco-friendly; returns nutrients to nature | Cause pollution; accumulate in the environment |
The 3 R's: Reduce (use less), Reuse (use again without reprocessing), Recycle (reprocess waste into new products). These help minimise the volume of waste entering our environment.
Indexed Topics & Examination Keywords
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