NCERT Science: Our Environment (Ecosystems, Food Chains, Ozone and Pollution)

The one-line takeaway

An ecosystem is a community of living organisms interacting with their non-living surroundings. Energy flows through it along food chains and webs, from producers to consumers, while matter is recycled by decomposers. Human activity has damaged the environment through ozone depletion, the enhanced greenhouse effect, waste and pollution, which is why conservation and waste management matter.

The ecosystem

• An ecosystem comprises biotic components (living things) and abiotic components (non-living: light, temperature, water, air, soil). It may be natural (forest, pond, ocean, grassland) or artificial (a crop field, an aquarium).
• The biotic components are grouped by their role:
  • Producers (autotrophs): green plants, which make food by photosynthesis and form the base of every food chain.
  • Consumers (heterotrophs): herbivores (primary consumers), carnivores (secondary and higher consumers) and omnivores.
  • Decomposers: bacteria and fungi that break down dead matter, returning nutrients to the soil and completing the cycle.

Food chains, food webs and energy flow

• A food chain is the sequence of who eats whom: for example grass to grasshopper to frog to snake to eagle. Each step is a trophic level.
• Real ecosystems are not simple chains but interconnected food webs, since most organisms eat and are eaten by several others.
• Energy flow is one-way: it enters as sunlight, is fixed by producers, and passes up the chain, but it is not recycled (unlike matter). At each trophic level only about 10 percent of the energy is passed on (the "ten percent law"), the rest being lost as heat, which is why food chains rarely have more than four or five links.
• Biomagnification: non-biodegradable poisons (such as certain pesticides) become more concentrated as they pass up the food chain, so top predators (and humans) accumulate the highest, most harmful doses.

The ozone layer

• The ozone layer, high in the stratosphere, absorbs most of the Sun's harmful ultraviolet radiation, shielding life (preventing skin cancer, cataract and damage to crops).
• It is depleted by man-made chlorofluorocarbons (CFCs), once used in refrigerants, aerosols and foam, which release chlorine that destroys ozone, producing the "ozone hole" over Antarctica.
• The international response is the Montreal Protocol (1987), under which countries agreed to phase out ozone-depleting substances; it is regarded as the most successful environmental treaty, and the ozone layer is slowly recovering. Verify the latest assessment.

The greenhouse effect and global warming

• The greenhouse effect is the natural trapping of heat by gases (carbon dioxide, methane, water vapour, nitrous oxide) that keep the Earth warm enough for life. The problem is the enhanced greenhouse effect caused by burning fossil fuels and deforestation, which raises these gases and drives global warming and climate change.
• Consequences include melting glaciers and polar ice, rising sea levels, more extreme weather, shifting monsoons and threats to agriculture and coastal populations. The global response runs through the United Nations climate framework and the Paris Agreement (2015).

Waste and pollution

• Biodegradable waste is broken down by decomposers (food scraps, paper, cotton); non-biodegradable waste is not, or only very slowly (plastics, glass, metals, certain chemicals), so it accumulates and pollutes.
• Pollution is the contamination of the environment by harmful substances. Major types:
  • Air pollution: from vehicles, industry and burning, causing respiratory disease, smog and acid rain.
  • Water pollution: from sewage, industrial effluent, fertilisers and pesticides, harming aquatic life and human health.
  • Soil pollution: from chemicals, plastics and waste.
  • Noise pollution: from traffic, industry and machinery, harming hearing and mental health.
• Management: segregation of waste at source, composting of biodegradable waste, recycling, proper effluent and sewage treatment, and the three Rs (reduce, reuse, recycle).

Key terms to fix

• Ecosystem: biotic plus abiotic components; producers, consumers, decomposers.
• Ten percent law: only about a tenth of the energy passes to the next trophic level; energy flow is one-way.
• Biomagnification: poisons concentrate up the food chain.
• Ozone depletion (CFCs) and the Montreal Protocol (1987).
• Greenhouse effect and global warming; the Paris Agreement (2015).
• Biodegradable versus non-biodegradable waste.

CAPF angle

Environmental degradation is treated as a security "threat multiplier": climate change worsens disasters, displacement and resource conflict, and the forces (through the National Disaster Response Force) are the front line in floods, cyclones, landslides and earthquakes. Pollution and waste are public-health concerns in camps and operational areas. The right to a clean environment is read into the right to life under Article 21, linking this topic to the human-rights lens.

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