Class 9 Science Chapter 13 Earth as a System: Energy, Matter and Life – Revision Notes

Quick revision notes for Class 9 Science Chapter 13 (Earth as a System: Energy, Matter and Life). These Class 9 Science Chapter 13 notes are ideal for quick revision just before exams.

Five Spheres

• Geosphere: solid Earth (rocks, minerals).
• Hydrosphere: all water (oceans, rivers, groundwater).
• Atmosphere: gases surrounding Earth.
• Cryosphere: frozen water (ice, glaciers, permafrost).
• Biosphere: all living organisms.

Solar Radiation

• Sun’s energy (electromagnetic spectrum) drives weather, climate, photosynthesis.

Differential Heating & Wind

• Uneven surface heating → pressure differences → wind (high → low pressure).

Biogeochemical Cycles

• Water cycle: evaporation → condensation → precipitation → collection.
• Carbon cycle: atmosphere ↔ organisms (photosynthesis/respiration) ↔ oceans/fossil fuels.
• Nitrogen cycle: atmosphere (N2) ↔ soil (fixation) ↔ organisms ↔ atmosphere (denitrification).
• Oxygen cycle: released by photosynthesis, consumed by respiration/combustion.

Human Impact

• Fossil fuels → excess CO2 (carbon cycle disruption).
• Fertiliser overuse → nitrogen cycle disruption.

One-Line Summary

Earth functions as one interconnected system of five spheres, powered by solar radiation, with differential heating driving winds and matter continuously recycled through the water, carbon, nitrogen, and oxygen cycles — cycles that human activity increasingly disrupts.

Written by Satish

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