CBSE Class 10 Biology — Chapter 13: Our Environment — Revision Notes

Overview: These revision notes cover ecosystems, components of environment, food chains and food webs, energy flow, nutrient cycles, ecological pyramids, biodiversity, pollution (air, water, soil, noise), waste management and conservation strategies — prepared strictly as per NCERT Class 10 Biology. Use this module for focused revision and exam preparation.

1. What is 'Environment' and an 'Ecosystem'?

The environment comprises all external factors (living and non-living) that affect organisms. It includes the atmosphere, hydrosphere (water bodies), lithosphere (land) and biosphere (living organisms).

An ecosystem is a functional unit consisting of a community of organisms (biotic components) interacting with each other and with their physical environment (abiotic components) in a given area. Examples: a pond, a forest, a paddy field.

2. Biotic and Abiotic Components

Biotic components include producers (autotrophs), consumers (heterotrophs) and decomposers. Producers (green plants and some bacteria) synthesize organic food using sunlight (photosynthesis).

• Producers: Green plants and certain microbes that convert inorganic to organic matter.
• Consumers: Primary (herbivores), secondary (carnivores), tertiary (top carnivores) and omnivores.
• Decomposers: Bacteria and fungi that break down dead organic matter, recycling nutrients back to the ecosystem.

Abiotic components are non-living factors like sunlight, temperature, water, soil, air, minerals and pH. These determine the distribution and productivity of organisms.

3. Food Chain, Food Web and Ecological Pyramids

A food chain is a linear sequence showing transfer of energy and nutrients from producers to successive consumers (e.g., grass → deer → tiger). Real ecosystems have multiple interlinked chains called food webs which illustrate the complexity and alternative pathways of energy flow.

Ecological pyramids are graphical models showing numbers, biomass or energy at each trophic level:

• Pyramid of Numbers: Number of organisms at each level (can be inverted sometimes).
• Pyramid of Biomass: Total dry weight of organisms at each level (usually upright in terrestrial ecosystems).
• Pyramid of Energy: Shows energy flow through trophic levels — always upright because energy diminishes at each level (approx. 10% rule).

4. Energy Flow in an Ecosystem

Energy flow is unidirectional — from sun to producers, then to consumers and finally to decomposers. Solar energy is captured by plants (photosynthesis) and stored as chemical energy. Only a fraction (~10%) of energy at one trophic level is transferred to the next level — the rest is lost as heat, respiration and waste. This explains why food chains rarely extend beyond 4–5 trophic levels.

5. Nutrient Cycling — Carbon and Nitrogen Cycles

Nutrient cycles ensure recycling of essential elements. Two important cycles are:

Carbon Cycle

Carbon moves between atmosphere (CO₂), biosphere (plants/animals), hydrosphere and lithosphere. Key processes:

• Photosynthesis: CO₂ → organic carbon in plants.
• Respiration: organic carbon → CO₂ released back to atmosphere.
• Decomposition: dead matter → CO₂ (and methane under anaerobic conditions).
• Combustion and fossil fuel burning release stored carbon as CO₂, enhancing greenhouse effect.

Nitrogen Cycle

Nitrogen is essential for proteins and nucleic acids. Main steps:

• Atmospheric N₂ is inert — made usable by nitrogen-fixing bacteria (Rhizobium in root nodules, free-living Azotobacter) converting N₂ → NH₃/NH₄⁺.
• Nitrification: NH₄⁺ → NO₂⁻ → NO₃⁻ by nitrifying bacteria.
• Assimilation: Plants take up NO₃⁻/NH₄⁺ to form amino acids.
• Denitrification: Denitrifying bacteria convert NO₃⁻ → N₂, returning nitrogen to atmosphere.
• Decomposition and excretion also return nitrogen to soil for recycling.

6. Biodiversity and Its Importance

Biodiversity is the variety of life at genetic, species and ecosystem levels. High biodiversity contributes to ecosystem stability, provides genetic resources for agriculture/medicine, supports ecosystem services (pollination, water purification) and ensures resilience against environmental change.

Threats to biodiversity include habitat destruction, pollution, over-exploitation, invasive species and climate change. Conservation strategies include protected areas (national parks, sanctuaries), afforestation, habitat restoration and legal protection of species.

7. Pollution — Types, Sources and Effects

Pollution is the undesirable alteration of natural environment due to anthropogenic activities. Main types relevant to NCERT:

Air Pollution

• Sources: Industrial smog, vehicle emissions, burning of fossil fuels, crop residue burning.
• Key pollutants: Particulate matter (PM₂.₅/PM₁₀), SO₂, NOx, CO, volatile organic compounds (VOCs), suspended particulates.
• Effects: Respiratory illnesses, acid rain (SO₂/NOx), global warming (CO₂), reduced visibility.

Water Pollution

• Sources: Industrial effluents, sewage, agricultural runoff (pesticides/fertilizers), oil spills.
• Effects: Eutrophication (nutrient enrichment causing algal blooms and oxygen depletion), contamination of drinking water, loss of aquatic life, biomagnification of toxic substances (e.g., pesticides, heavy metals).

Soil Pollution & Land Degradation

• Pesticide accumulation, heavy metals, improper disposal of solid wastes, salinization and deforestation lead to poor soil health and reduced agricultural productivity.

Noise Pollution

• High decibel levels from traffic, industries and loudspeakers cause hearing impairment, stress and disturbances in wildlife.

8. Waste Management — Reduce, Reuse, Recycle

Waste management aims to reduce environmental impact. The 3Rs are central:

• Reduce: Avoid unnecessary waste generation (e.g., less packaging, energy conservation).
• Reuse: Use products multiple times (glass jars, cloth bags).
• Recycle: Convert waste into new materials (paper, plastic recycling); compost organic waste to produce manure.

Sanitary landfills, incineration (with pollution control), and segregation at source (wet/dry) are common methods. Integrated waste management combines these with public awareness and legislation.

9. Ozone Depletion and Global Warming (Brief)

Ozone depletion in the stratosphere (ozone layer) is accelerated by chlorofluorocarbons (CFCs) and leads to increased UV-B reaching Earth causing skin cancer and ecological harm. International action (Montreal Protocol) has reduced CFC use.

Global warming (climate change) is driven by greenhouse gases (CO₂, CH₄, N₂O) from fossil fuel burning, deforestation and agriculture. Effects include changing weather patterns, sea-level rise and biodiversity loss.

10. Conservation and Sustainable Practices

Sustainable living involves using resources at rates that can be replenished. Key practices include:

• Afforestation and controlled logging, soil conservation and watershed management.
• Promotion of renewable energy (solar, wind), energy-efficient appliances and public transport.
• Water harvesting, efficient irrigation (drip, sprinkler) and minimizing chemical fertilizer/pesticide use.
• Community participation, environmental education and legal frameworks for conservation.

11. Important Diagrams & Practicals (What to Practice)

Practice drawing and labelling:

• A simple food chain and a food web with multiple links.
• An energy pyramid showing decreasing energy and biomass across trophic levels.
• Carbon and nitrogen cycle diagrams (label processes: photosynthesis, respiration, fixation, nitrification, denitrification).
• Pictorial examples of pollution sources and waste segregation (wet/dry/eco-friendly disposal).

12. Key Terms (Memorise these)

13. Sample Short Questions & Answers (Practice)

• Q: What is a producer? A: An organism (usually green plants) that makes its own food by photosynthesis.
• Q: Define biomagnification. A: Increase in concentration of toxic substances (e.g., DDT) along the food chain at successive trophic levels.
• Q: Why are energy pyramids always upright? A: Energy decreases at each trophic level because only a small fraction is transferred; most is lost as heat.

14. Sample Long-Answer Points (Exam-Wise)

For a 5–8 mark question describing nutrient cycles or pollution:

• Start with a concise definition.
• Use a labelled diagram (where applicable).
• List key steps/processes in sequence (use bullets or numbering in your answer script).
• Explain significance or consequences (e.g., effect of eutrophication on aquatic life).
• End with a brief sentence on prevention or control measures.

15. Quick Revision Checklist (One-page)

• Definitions: ecosystem, producer, consumer, decomposer, biodiversity.
• Food chain vs food web; practice one each.
• Energy flow — 10% rule, pyramid of energy.
• Carbon and nitrogen cycle steps & key bacterial roles.
• Types of pollution — sources, effects, control measures.
• Waste management: segregation, composting, recycling, sanitary landfill basics.
• Conservation strategies and sustainable practices.