NCERT Science: Natural Resources and the Biogeochemical Cycles

The one-line takeaway

Natural resources are the materials and energy nature provides: air, water, soil, minerals and the living world. Vital elements are recycled through the biogeochemical cycles (water, carbon, oxygen, nitrogen). Resources are renewable or non-renewable, and conservation, through the three Rs and sustainable use, is essential because the non-renewable ones are finite.

Air

• The atmosphere is the blanket of air around the Earth. By volume, dry air is about 78 percent nitrogen and 21 percent oxygen, with the rest argon, carbon dioxide (a small but climatically crucial fraction) and traces of other gases, plus water vapour.
• The atmosphere moderates temperature (preventing extreme day-night swings), shields life from harmful radiation, and drives winds (caused by uneven heating of land and sea) and the weather.

Water

• Water covers most of the Earth's surface but only a small fraction is fresh and accessible. It is essential for all life, dissolving and transporting substances and regulating temperature.
• The water cycle (hydrological cycle): solar heating evaporates water from oceans and surfaces; plants add water by transpiration; the vapour rises, cools and condenses into clouds; it falls as precipitation (rain, snow); it flows over and under the land back to the seas. The cycle distributes fresh water and shapes climate.

Soil

• Soil is the thin top layer that supports plant life; it forms very slowly over thousands of years by the weathering of rock (by sun, water, wind and biological action) mixed with humus (decayed organic matter).
• Soil erosion (the removal of fertile topsoil by wind and water, worsened by deforestation and over-grazing) is a serious threat; it is controlled by afforestation, contour ploughing, terracing and check dams.

The biogeochemical cycles

• Carbon cycle: carbon moves between the atmosphere (as carbon dioxide), living things and the Earth. Plants take in carbon dioxide in photosynthesis; respiration, decay and the burning of fuels return it. Burning fossil fuels adds carbon dioxide faster than it is removed, intensifying the greenhouse effect.
• Oxygen cycle: oxygen is released by photosynthesis and consumed in respiration, combustion and decay; it also forms the protective ozone layer high in the atmosphere.
• Nitrogen cycle: nitrogen gas is abundant in air but unusable directly by most life. Nitrogen fixation (by lightning and by bacteria in the root nodules of leguminous plants, such as Rhizobium) converts it into usable compounds; plants and animals use it; decomposition and denitrification return nitrogen to the air. The cycle keeps soil fertile.

Energy resources

• Renewable resources can be replenished naturally within a human timescale: solar, wind, hydro (flowing water), tidal, geothermal and biomass energy, and living resources such as forests and fisheries (if not over-used).
• Non-renewable resources are finite and take millions of years to form: the fossil fuels (coal, petroleum, natural gas) and minerals. Burning fossil fuels powers most of the economy but causes air pollution and climate change and will eventually run out.
• Nuclear energy uses the fission of heavy atoms (uranium); it gives large energy from little fuel but raises issues of radioactive waste and safety.

Conservation

• Because resources are finite and the environment has a limited carrying capacity, conservation is essential. The guiding principle is the three Rs: reduce, reuse, recycle (some add refuse and repair).
• Specific measures: afforestation and protection of forests, rainwater harvesting and watershed management, soil conservation, energy efficiency, a shift to renewables, and laws to protect resources. India's forest and wildlife laws and the campaign for sustainable use feed into our environment.

Key terms to fix

• Air composition: about 78 percent nitrogen, 21 percent oxygen.
• Water cycle: evaporation and transpiration, condensation, precipitation, runoff.
• Nitrogen fixation: lightning and Rhizobium bacteria convert air nitrogen into usable form.
• Renewable versus non-renewable resources: solar, wind, hydro versus coal, oil, gas, minerals.
• The three Rs: reduce, reuse, recycle.

CAPF angle

Natural resources are increasingly a matter of national and human security. Water security (shared rivers, dwindling groundwater) is a source of inter-State and international tension; energy security drives strategy on oil, gas and the shift to renewables; and control of forests and minerals is entangled with the conflict over land rights and left-wing extremism in resource-rich tribal belts. Soil and water conservation are also central to the disaster-mitigation role the forces share.

Authored practice

1. The two most abundant gases in the Earth's atmosphere by volume are: (a) oxygen and carbon dioxide (b) nitrogen and oxygen (c) carbon dioxide and argon (d) hydrogen and helium. (Answer: b, about 78 percent nitrogen and 21 percent oxygen.) Authored practice, not a verbatim PYQ.
2. Biological nitrogen fixation in the root nodules of leguminous plants is carried out chiefly by which bacterium? (Answer: Rhizobium.) Authored practice, not a verbatim PYQ.