Science Exploration Notes Class 9 English Medium 2026-27

Science Exploration Chapter 13. Earth as a System: Energy, Matter, and Life

CBSE Notes New Syllabus: Class 9

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Chapter 13. Earth as a System: Energy, Matter, and Life

This section explains Biogeochemical Cycles, which recycle essential elements between the living and non-living components of the Earth. It covers the Water Cycle and Carbon Cycle, showing how these cycles maintain environmental balance and support life. 

Biogeochemical Cycles

Biogeochemical Cycle

A biogeochemical cycle is the continuous movement and recycling of matter and nutrients between the biotic (living) and abiotic (non-living) components of the Earth. These cycles maintain the balance of essential elements required for life. 

Importance of Biogeochemical Cycles

• Recycle essential nutrients.
• Maintain ecological balance.
• Support plant and animal life.
• Connect Earth's different spheres.
• Help ecosystems recover from disturbances.

Main Biogeochemical Cycles

• Water Cycle
• Carbon Cycle
• Nitrogen Cycle
• Oxygen Cycle

Water Cycle

Water Cycle

The water cycle is the continuous circulation of water between the atmosphere, land, rivers, oceans and groundwater through various natural processes. 

Main Processes of the Water Cycle

Importance of the Water Cycle

• Maintains freshwater supply.
• Recharges groundwater.
• Supports agriculture.
• Transports nutrients.
• Maintains aquatic ecosystems.

Effect of Climate Change on the Water Cycle

• Heavier rainfall in some regions.
• Frequent droughts in other regions.
• Rapid melting of glaciers.
• Rise in sea level.
• Reduced groundwater recharge.
• Increased soil erosion.

Carbon Cycle

Carbon Cycle

The carbon cycle is the continuous movement of carbon between the atmosphere, biosphere, hydrosphere and geosphere. Carbon is an essential element of proteins, carbohydrates, fats and DNA. 

Fast Carbon Cycle

• Plants absorb CO₂ during photosynthesis.
• Animals obtain carbon by feeding on plants.
• Respiration releases CO₂ into the atmosphere.
• Decomposition returns carbon to the environment.

Slow Carbon Cycle

• Dead organisms form fossil fuels over millions of years.
• Burning fossil fuels releases stored carbon as CO₂.
• Oceans absorb atmospheric CO₂.
• Marine organisms use carbon to form shells.
• Carbon remains stored in ocean sediments for long periods.

Human Impact on the Carbon Cycle

• Burning fossil fuels increases atmospheric CO₂.
• Deforestation reduces carbon absorption.
• Higher CO₂ strengthens the greenhouse effect.
• Results in global warming and climate change.

Key Terms at a Glance

Our Concept Builder

Biogeochemical cycles continuously recycle matter between the atmosphere, hydrosphere, geosphere and biosphere. The water cycle ensures the availability of freshwater, while the carbon cycle regulates atmospheric carbon dioxide and helps maintain the Earth's climate and life-support system. 

Our Exam Booster

• Define biogeochemical cycle.
• Remember the six stages of the water cycle.
• Know the difference between the fast and slow carbon cycles.
• Understand the role of photosynthesis and respiration.
• Learn how climate change affects the water cycle.
• Know how burning fossil fuels and deforestation disturb the carbon cycle.
• CBSE competency-based questions may ask students to explain how the water and carbon cycles connect different Earth spheres.