Earth as a System, Part 2: cycles of matter and human impact: visual lesson, CBSE Class 9 Science

Lesson

Cycles of matter and our impact

Part 2: carbon, nitrogen and water cycles, and what people do to them.

In this lesson you will

Explain the carbon, nitrogen and water cycles
Describe nitrogen fixation, nitrification and denitrification
Describe how human activities affect the cycles and the climate, and suggest actions

Concept

Energy flows, matter cycles

Sunlight arrives, does its work and leaves as heat. Matter has nowhere else to go, so it cycles between air, water, rock and living things.

Table comparing the flow of energy with the cycling of matter on Earth
	Energy	Matter
Source	Comes from the Sun	Already on Earth
What happens	Flows through and leaves as heat	Goes round and round in cycles
Examples	Sunlight, then heat to space	Carbon, nitrogen, water

Concept

The carbon cycle

Plants and algae take carbon dioxide from the air by photosynthesis. Animals eat plants. Respiration and decomposition return carbon dioxide to the air. Some remains become fossil fuels, and burning them releases carbon dioxide. The ocean takes in and gives out carbon dioxide.

The carbon cycle: schematic.

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