Natural Resources and Nature's Cycles: Class 9 Study Guide
Nature recycles materials such as water, carbon and nitrogen. Human activities can disturb these cycles.
The atmosphere is the layer of air around the Earth. It is about 78% nitrogen and 21% oxygen, with small amounts of argon, carbon dioxide and water vapour. Air moves because land warms faster than water, giving winds and, in India, the monsoon. Water covers most of the Earth, but only a small part is fresh and available.
Soil forms slowly from rocks by weathering and the action of living things.
The cycles
| Cycle | Key idea |
|---|---|
| Water | Evaporation, condensation, precipitation and run-off |
| Carbon | Photosynthesis takes in CO₂; respiration, burning and decay return it |
| Nitrogen | Bacteria in roots of pulses fix nitrogen; plants make proteins; decay returns it |
| Oxygen | Photosynthesis releases it; respiration and burning use it |
Human impact
Burning fuel adds carbon dioxide, which traps heat in the greenhouse effect, and too much of it causes global warming. Chemicals called CFCs damaged the ozone layer, which shields us from harmful ultraviolet light, and they have been phased out. Sulphur and nitrogen oxides from smoke cause acid rain. Smoke and dust are air pollutants, and dumping waste pollutes water and soil.
Adds gases and smoke.
Greenhouse effect.
Weather changes.
Save energy and plant trees.
What can we do?
Plant trees, use public transport, save water and electricity, avoid burning waste and reduce, reuse and recycle. Farmers can use crop rotation with pulses to add nitrogen to the soil naturally.
Worked examples and common mistakes
Example: Why do farmers grow pulses in rotation? Bacteria in their roots fix nitrogen and enrich the soil. Example: Which gas is most of the air? Nitrogen. Common mistakes: thinking that the ozone hole and the greenhouse effect are the same problem, and thinking that oxygen is the main gas in air. They are different problems with different causes.
Check your understanding: model answers
1. Nitrogen. 2. Bacteria in their root nodules fix nitrogen into a form plants can use. 3. Harmful ultraviolet radiation from the Sun.
✨ Key Takeaways
- Air is about 78% nitrogen and 21% oxygen.
- Water, carbon and nitrogen are recycled in nature.
- Burning fuels adds to global warming.
- We can reduce pollution with small daily actions.
💬 Questions for Discussion & Reflection
- Name the gas that makes up most of the air.
- How do pulses help the soil?
- What does the ozone layer protect us from?
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