Natural Resources
The paper tests the composition of air, the water and soil cycles, forests and fossil fuels, biogeochemical cycles, the ozone layer and conservation practices.
Resources and cycles
Air is about 78% nitrogen, 21% oxygen and 0.03–0.04% carbon dioxide, with inert gases and water vapour. Water moves by evaporation, condensation, precipitation and run-off. The carbon cycle moves carbon through photosynthesis, respiration, decomposition and combustion. The nitrogen cycle uses nitrogen-fixing bacteria such as Rhizobium and Azotobacter plus lightning, nitrifying bacteria to nitrites and nitrates, assimilation by plants, ammonification by decomposers, and denitrification back to N2.
Soil, forests and fuels
Soil forms by weathering of rock plus humus from decomposed matter; erosion by wind and water is worsened by deforestation and overgrazing. Forests prevent erosion, recharge groundwater and maintain biodiversity. Fossil fuels such as coal, petroleum and natural gas are non-renewable and add carbon dioxide to the atmosphere.
Conservation
- Rainwater harvesting stores rain for reuse and raises the water table.
- Watershed management conserves soil and water in a catchment using check dams and contour bunds.
- Dams supply water and power but displace people and submerge forests, a real trade-off.
- Reduce, reuse and recycle; protect wildlife reserves.
Worked example
Trace a nitrogen atom from air to a plant protein. N2 in air is fixed as ammonia by Rhizobium in root nodules, nitrifying bacteria convert it to nitrite and then nitrate, roots absorb nitrate and build amino acids and proteins, consumers eat the plant, decomposers release ammonia, and denitrifying bacteria return N2 to the air.
Traps
Nitrogen-fixing bacteria live in root nodules, not in leaves; carbon dioxide is a greenhouse gas but not a toxic pollutant like sulphur dioxide; conservation means wise use, not total non-use.