Earth as a System: Energy, Matter, and Life

Quick answer

Earth as a System: Energy, Matter, and Life is Chapter 13 of NCERT Class 9 Science, Exploration. It introduces interactions among Earth's matter, energy and living systems.

Key points

Earth can be studied as interacting subsystems. Changes in one subsystem can influence the others through exchanges of energy and matter.
The atmosphere is the envelope of gases around Earth, dominated near the surface by nitrogen and oxygen.
The hydrosphere includes Earth's water in oceans, rivers, lakes, groundwater and ice, though frozen water is sometimes treated as a separate cryosphere.
The geosphere includes rocks, minerals, soils and Earth's solid interior.
The biosphere comprises living organisms and the regions they inhabit.
A system boundary is chosen for analysis; a system may exchange matter, energy or both with its surroundings.
Sunlight powers photosynthesis and many atmospheric and water-cycle processes.
Geothermal heat contributes to plate tectonics, volcanism and some hot springs.
Earth receives solar radiation and emits infrared radiation; long-term energy imbalance changes temperature.
Greenhouse gases absorb and emit infrared radiation, warming the surface relative to an atmosphere without those gases.
Weather describes short-term atmospheric conditions; climate describes long-term patterns and statistics.
Evaporation changes liquid water to vapour; transpiration releases water vapour from plants.
Cooling or other changes can cause water vapour to condense onto tiny particles, forming cloud droplets.
Water falls from clouds as rain, snow, sleet or hail depending on conditions.
Some precipitation flows over land, some infiltrates and some percolates to groundwater.

Use these notes alongside your current textbook. Check important formulas, worked answers and syllabus coverage with your teacher or official learning material.

Class 9 NCERT Exploration (2026–27), Chapter 13. This expanded original supplementary study guide explains interconnected Earth systems, energy flow, matter cycles, ecosystems and human impacts. The exact NCERT numbered exercises, illustrations and classroom activities have not been verified page by page; original questions below must not be confused with official textbook exercises.

Learning outcomes

Describe interactions among atmosphere, hydrosphere, geosphere and biosphere.
Trace water, carbon and nutrients through different reservoirs.
Distinguish energy flow from matter cycling.
Explain ecosystem processes and evaluate human influences.
Solve basic water-budget calculations and interpret evidence responsibly.

Earth as an interacting system

Earth can be studied as interacting subsystems. Changes in one subsystem can influence the others through exchanges of energy and matter.

Example

A volcanic eruption transfers material from the geosphere into the atmosphere.

Atmosphere

The atmosphere is the envelope of gases around Earth, dominated near the surface by nitrogen and oxygen.

Example

Clouds form when atmospheric water vapour condenses into droplets or ice crystals.

Hydrosphere

The hydrosphere includes Earth's water in oceans, rivers, lakes, groundwater and ice, though frozen water is sometimes treated as a separate cryosphere.

Example

Rainwater infiltrates soil and may recharge groundwater.

Geosphere

The geosphere includes rocks, minerals, soils and Earth's solid interior.

Example

Weathering breaks rocks into smaller particles.

Biosphere

The biosphere comprises living organisms and the regions they inhabit.

Example

Plant roots interact with soil, water and air.

System boundaries

A system boundary is chosen for analysis; a system may exchange matter, energy or both with its surroundings.

Example

A pond receives sunlight, rain and dissolved nutrients.

Solar energy

Sunlight powers photosynthesis and many atmospheric and water-cycle processes.

Example

Solar heating promotes evaporation from lakes.

Earth's internal energy

Geothermal heat contributes to plate tectonics, volcanism and some hot springs.

Example

Hot springs can be warmed by geothermal energy.

Radiation and energy balance

Earth receives solar radiation and emits infrared radiation; long-term energy imbalance changes temperature.

Example

Clouds can reflect incoming sunlight and absorb outgoing infrared radiation.

Greenhouse effect

Greenhouse gases absorb and emit infrared radiation, warming the surface relative to an atmosphere without those gases.

Example

Carbon dioxide and water vapour contribute to the natural greenhouse effect.

Weather and climate

Weather describes short-term atmospheric conditions; climate describes long-term patterns and statistics.

Example

A rainy day is weather; typical monsoon-season rainfall is part of climate.

Evaporation and transpiration

Evaporation changes liquid water to vapour; transpiration releases water vapour from plants.

Example

Leaves release water vapour through stomata.

Condensation and clouds

Cooling or other changes can cause water vapour to condense onto tiny particles, forming cloud droplets.

Example

Moist air rising and cooling may form clouds.

Precipitation

Water falls from clouds as rain, snow, sleet or hail depending on conditions.

Example

Rainfall supplies water to rivers and soil.

Runoff, infiltration and groundwater

Some precipitation flows over land, some infiltrates and some percolates to groundwater.

Example

Paved surfaces often increase surface runoff.

Water-cycle conservation

Water moves between reservoirs and changes state; the total amount is approximately conserved over ordinary Earth-system timescales.

Example

Evaporated ocean water may later fall as rain over land.

Carbon reservoirs

Carbon is stored in atmosphere, oceans, soils, rocks and living organisms.

Example

Forests store carbon in wood and soils.

Photosynthesis

Photosynthetic organisms use light energy to build organic molecules from carbon dioxide and water, releasing oxygen in oxygenic photosynthesis.

Example

Plants convert carbon dioxide into carbohydrates.

Respiration

Cells release usable energy by breaking down organic molecules; aerobic respiration generally produces carbon dioxide and water.

Example

Animals release CO₂ during cellular respiration.

Decomposition

Decomposers break down dead organic matter, recycling nutrients and releasing carbon compounds.

Example

Fungi decompose fallen leaves.

Combustion and fossil fuels

Burning carbon-based fuels transfers carbon from fuel to atmosphere, commonly as CO₂.

Example

Burning coal emits carbon dioxide.

Nitrogen cycle

Nitrogen fixation, nitrification, assimilation, ammonification and denitrification move nitrogen among forms and reservoirs.

Example

Certain bacteria convert atmospheric nitrogen into biologically available compounds.

Food chains and webs

Producers capture energy; consumers obtain energy by feeding; decomposers recycle matter.

Example

Grass → grasshopper → frog is a simplified food chain.

Energy transfer in ecosystems

Energy enters many ecosystems as sunlight and is dissipated as heat across transfers; nutrients and matter are recycled.

Example

Only a portion of energy consumed by a herbivore becomes new biomass.

Trophic levels

Organisms can be grouped by feeding role; food webs are more realistic than a single chain.

Example

A hawk may feed on several species at different trophic positions.

Soil formation

Weathering, organic matter, organisms, water and time contribute to soil development.

Example

Earthworms help mix soil and organic matter.

Erosion and deposition

Water, wind and ice transport and deposit sediments, reshaping landscapes.

Example

A river deposits silt on its floodplain.

Human land-use change

Deforestation, urbanisation and agriculture alter water, carbon and nutrient cycling.

Example

Removing vegetation can increase erosion and runoff.

Pollution and eutrophication

Excess nutrients entering water can stimulate algal blooms and reduce dissolved oxygen when biomass decomposes.

Example

Fertiliser runoff may contribute to lake eutrophication.

Climate change and feedbacks

Rising greenhouse-gas concentrations alter Earth's energy balance; feedbacks can amplify or dampen changes.

Example

Melting ice reduces reflectivity and can increase absorbed solar energy.

Biodiversity and resilience

Biodiversity can support ecosystem functioning, but resilience depends on context and disturbances.

Example

Different plant species may respond differently to drought.

Sustainable resource use

Conservation, efficient use, pollution control and ecosystem restoration can reduce human pressures.

Example

Rainwater harvesting can supplement local water supplies where appropriate.

Observing Earth systems

Measurements, maps, satellite data and long-term records help test explanations about Earth.

Example

Record rainfall and temperature over time using consistent units.

Model limitations

Simplified diagrams omit some pathways and timescales; avoid treating arrows as exhaustive.

Example

A water-cycle diagram may omit groundwater storage and human water use.

Reference table

Topic	Essential concept	Example
Earth as an interacting system	Earth can be studied as interacting subsystems. Changes in one subsystem can influence the others through exchanges of energy and matter.	A volcanic eruption transfers material from the geosphere into the atmosphere.
Atmosphere	The atmosphere is the envelope of gases around Earth, dominated near the surface by nitrogen and oxygen.	Clouds form when atmospheric water vapour condenses into droplets or ice crystals.
Hydrosphere	The hydrosphere includes Earth's water in oceans, rivers, lakes, groundwater and ice, though frozen water is sometimes treated as a separate cryosphere.	Rainwater infiltrates soil and may recharge groundwater.
Geosphere	The geosphere includes rocks, minerals, soils and Earth's solid interior.	Weathering breaks rocks into smaller particles.
Biosphere	The biosphere comprises living organisms and the regions they inhabit.	Plant roots interact with soil, water and air.
System boundaries	A system boundary is chosen for analysis; a system may exchange matter, energy or both with its surroundings.	A pond receives sunlight, rain and dissolved nutrients.
Solar energy	Sunlight powers photosynthesis and many atmospheric and water-cycle processes.	Solar heating promotes evaporation from lakes.
Earth's internal energy	Geothermal heat contributes to plate tectonics, volcanism and some hot springs.	Hot springs can be warmed by geothermal energy.
Radiation and energy balance	Earth receives solar radiation and emits infrared radiation; long-term energy imbalance changes temperature.	Clouds can reflect incoming sunlight and absorb outgoing infrared radiation.
Greenhouse effect	Greenhouse gases absorb and emit infrared radiation, warming the surface relative to an atmosphere without those gases.	Carbon dioxide and water vapour contribute to the natural greenhouse effect.
Weather and climate	Weather describes short-term atmospheric conditions; climate describes long-term patterns and statistics.	A rainy day is weather; typical monsoon-season rainfall is part of climate.
Evaporation and transpiration	Evaporation changes liquid water to vapour; transpiration releases water vapour from plants.	Leaves release water vapour through stomata.
Condensation and clouds	Cooling or other changes can cause water vapour to condense onto tiny particles, forming cloud droplets.	Moist air rising and cooling may form clouds.
Precipitation	Water falls from clouds as rain, snow, sleet or hail depending on conditions.	Rainfall supplies water to rivers and soil.
Runoff, infiltration and groundwater	Some precipitation flows over land, some infiltrates and some percolates to groundwater.	Paved surfaces often increase surface runoff.
Water-cycle conservation	Water moves between reservoirs and changes state; the total amount is approximately conserved over ordinary Earth-system timescales.	Evaporated ocean water may later fall as rain over land.
Carbon reservoirs	Carbon is stored in atmosphere, oceans, soils, rocks and living organisms.	Forests store carbon in wood and soils.
Photosynthesis	Photosynthetic organisms use light energy to build organic molecules from carbon dioxide and water, releasing oxygen in oxygenic photosynthesis.	Plants convert carbon dioxide into carbohydrates.
Respiration	Cells release usable energy by breaking down organic molecules; aerobic respiration generally produces carbon dioxide and water.	Animals release CO₂ during cellular respiration.
Decomposition	Decomposers break down dead organic matter, recycling nutrients and releasing carbon compounds.	Fungi decompose fallen leaves.
Combustion and fossil fuels	Burning carbon-based fuels transfers carbon from fuel to atmosphere, commonly as CO₂.	Burning coal emits carbon dioxide.
Nitrogen cycle	Nitrogen fixation, nitrification, assimilation, ammonification and denitrification move nitrogen among forms and reservoirs.	Certain bacteria convert atmospheric nitrogen into biologically available compounds.
Food chains and webs	Producers capture energy; consumers obtain energy by feeding; decomposers recycle matter.	Grass → grasshopper → frog is a simplified food chain.
Energy transfer in ecosystems	Energy enters many ecosystems as sunlight and is dissipated as heat across transfers; nutrients and matter are recycled.	Only a portion of energy consumed by a herbivore becomes new biomass.
Trophic levels	Organisms can be grouped by feeding role; food webs are more realistic than a single chain.	A hawk may feed on several species at different trophic positions.
Soil formation	Weathering, organic matter, organisms, water and time contribute to soil development.	Earthworms help mix soil and organic matter.
Erosion and deposition	Water, wind and ice transport and deposit sediments, reshaping landscapes.	A river deposits silt on its floodplain.
Human land-use change	Deforestation, urbanisation and agriculture alter water, carbon and nutrient cycling.	Removing vegetation can increase erosion and runoff.
Pollution and eutrophication	Excess nutrients entering water can stimulate algal blooms and reduce dissolved oxygen when biomass decomposes.	Fertiliser runoff may contribute to lake eutrophication.
Climate change and feedbacks	Rising greenhouse-gas concentrations alter Earth's energy balance; feedbacks can amplify or dampen changes.	Melting ice reduces reflectivity and can increase absorbed solar energy.
Biodiversity and resilience	Biodiversity can support ecosystem functioning, but resilience depends on context and disturbances.	Different plant species may respond differently to drought.
Sustainable resource use	Conservation, efficient use, pollution control and ecosystem restoration can reduce human pressures.	Rainwater harvesting can supplement local water supplies where appropriate.
Observing Earth systems	Measurements, maps, satellite data and long-term records help test explanations about Earth.	Record rainfall and temperature over time using consistent units.
Model limitations	Simplified diagrams omit some pathways and timescales; avoid treating arrows as exhaustive.	A water-cycle diagram may omit groundwater storage and human water use.

Original exercise 1: Solved questions and answers

Question: Name four interacting Earth subsystems.
Answer: Atmosphere (air), hydrosphere (water), geosphere (solid Earth) and biosphere (life).
Question: Explain one way the biosphere influences the atmosphere.
Answer: Photosynthesis removes carbon dioxide from air and releases oxygen; respiration returns carbon dioxide.
Question: What is the difference between weather and climate?
Answer: Weather concerns short-term conditions; climate concerns long-term statistics and patterns.
Question: Why does evaporation require energy?
Answer: Liquid water molecules need energy to overcome intermolecular attractions and enter the vapour phase.
Question: How can deforestation affect runoff?
Answer: Reduced vegetation and soil structure changes can lower interception and infiltration, increasing surface runoff in many settings.
Question: What happens to water vapour during condensation?
Answer: It changes into liquid droplets, releasing latent heat to surroundings.
Question: Give three stores of carbon.
Answer: Atmosphere, oceans and living biomass; soils and sedimentary rocks are other major stores.
Question: How do respiration and photosynthesis differ in their carbon flow?
Answer: Photosynthesis generally fixes CO₂ into organic matter; aerobic respiration oxidises organic matter and releases CO₂.
Question: Why is energy flow not called an energy cycle in ecosystems?
Answer: Energy enters, transfers and eventually dissipates as heat; matter such as carbon and nitrogen cycles through reservoirs.
Question: A pond receives 120 mm rain and loses 80 mm to evaporation during a period, with no other flows. What is net water-depth change?
Answer: 120−80=40 mm increase, assuming uniform area and no inflow, runoff, infiltration or withdrawal.
Question: A rooftop receives 0.05 m of rain over 100 m². Estimate water volume before losses.
Answer: V=depth×area=0.05×100=5 m³=5000 litres.
Question: If a reservoir receives 600 m³ and loses 450 m³ during a day, what is net change?
Answer: 600−450=150 m³ gain, assuming those are the only transfers.
Question: Why can fertiliser runoff harm aquatic life?
Answer: Added nutrients may cause algal blooms; decomposition can consume dissolved oxygen, harming aquatic organisms.
Question: What is the natural greenhouse effect?
Answer: Greenhouse gases absorb and emit infrared radiation, making Earth's surface warmer than it would be without them.
Question: Why does melting reflective ice sometimes accelerate warming?
Answer: Less reflective ice exposes darker surfaces that absorb more sunlight, a positive ice-albedo feedback.
Question: How can soil act as a carbon store?
Answer: Organic matter from plants and organisms can accumulate in soil and hold carbon for varying periods.
Question: What is the role of decomposers in nutrient cycles?
Answer: They break down organic matter, returning nutrients to soil, water and air in usable forms.
Question: Why are food webs more realistic than food chains?
Answer: Most organisms have multiple food sources and predators, creating interconnected feeding relationships.
Question: Give two examples of Earth-system observations students can make safely.
Answer: Measure rainfall with a rain gauge and record local temperature at a consistent time using a suitable thermometer.
Question: What is a limitation of a simple water-cycle diagram?
Answer: It may omit groundwater, human withdrawals, seasonal storage, oceans and different timescales.

Original exercise 2: Topic-based short answers

Question: Explain earth as an interacting system.
Answer: Earth can be studied as interacting subsystems. Changes in one subsystem can influence the others through exchanges of energy and matter.
Question: Explain atmosphere.
Answer: The atmosphere is the envelope of gases around Earth, dominated near the surface by nitrogen and oxygen.
Question: Explain hydrosphere.
Answer: The hydrosphere includes Earth's water in oceans, rivers, lakes, groundwater and ice, though frozen water is sometimes treated as a separate cryosphere.
Question: Explain geosphere.
Answer: The geosphere includes rocks, minerals, soils and Earth's solid interior.
Question: Explain biosphere.
Answer: The biosphere comprises living organisms and the regions they inhabit.
Question: Explain system boundaries.
Answer: A system boundary is chosen for analysis; a system may exchange matter, energy or both with its surroundings.
Question: Explain solar energy.
Answer: Sunlight powers photosynthesis and many atmospheric and water-cycle processes.
Question: Explain earth's internal energy.
Answer: Geothermal heat contributes to plate tectonics, volcanism and some hot springs.
Question: Explain radiation and energy balance.
Answer: Earth receives solar radiation and emits infrared radiation; long-term energy imbalance changes temperature.
Question: Explain greenhouse effect.
Answer: Greenhouse gases absorb and emit infrared radiation, warming the surface relative to an atmosphere without those gases.
Question: Explain weather and climate.
Answer: Weather describes short-term atmospheric conditions; climate describes long-term patterns and statistics.
Question: Explain evaporation and transpiration.
Answer: Evaporation changes liquid water to vapour; transpiration releases water vapour from plants.
Question: Explain condensation and clouds.
Answer: Cooling or other changes can cause water vapour to condense onto tiny particles, forming cloud droplets.
Question: Explain precipitation.
Answer: Water falls from clouds as rain, snow, sleet or hail depending on conditions.
Question: Explain runoff, infiltration and groundwater.
Answer: Some precipitation flows over land, some infiltrates and some percolates to groundwater.
Question: Explain water-cycle conservation.
Answer: Water moves between reservoirs and changes state; the total amount is approximately conserved over ordinary Earth-system timescales.
Question: Explain carbon reservoirs.
Answer: Carbon is stored in atmosphere, oceans, soils, rocks and living organisms.
Question: Explain photosynthesis.
Answer: Photosynthetic organisms use light energy to build organic molecules from carbon dioxide and water, releasing oxygen in oxygenic photosynthesis.

Original exercise 3: Application and reasoning

Draw a four-sphere interaction diagram and explain five matter or energy transfers.
Draw a water-cycle flow diagram including evaporation, transpiration, condensation, precipitation, infiltration, groundwater and runoff.
Trace a carbon atom from the atmosphere to a plant, then to an animal and back to the atmosphere.
Compare an energy-flow diagram with a nutrient-cycle diagram, explaining why one is not a closed cycle.
Explain how urban paving may alter runoff and groundwater recharge, including exceptions.
Propose a safe rainfall-monitoring investigation, stating measurements, units and uncertainties.
Construct a water budget for a pond, explicitly listing inflows and outflows.
Evaluate one local environmental problem by identifying affected Earth subsystems and evidence needed.

FAQs

Name four interacting Earth subsystems.

Atmosphere (air), hydrosphere (water), geosphere (solid Earth) and biosphere (life).

Explain one way the biosphere influences the atmosphere.

Photosynthesis removes carbon dioxide from air and releases oxygen; respiration returns carbon dioxide.

What is the difference between weather and climate?

Weather concerns short-term conditions; climate concerns long-term statistics and patterns.

Why does evaporation require energy?

Liquid water molecules need energy to overcome intermolecular attractions and enter the vapour phase.

How can deforestation affect runoff?

Reduced vegetation and soil structure changes can lower interception and infiltration, increasing surface runoff in many settings.

What happens to water vapour during condensation?

It changes into liquid droplets, releasing latent heat to surroundings.

Give three stores of carbon.

Atmosphere, oceans and living biomass; soils and sedimentary rocks are other major stores.

How do respiration and photosynthesis differ in their carbon flow?

Photosynthesis generally fixes CO₂ into organic matter; aerobic respiration oxidises organic matter and releases CO₂.

Why is energy flow not called an energy cycle in ecosystems?

Energy enters, transfers and eventually dissipates as heat; matter such as carbon and nitrogen cycles through reservoirs.

A pond receives 120 mm rain and loses 80 mm to evaporation during a period, with no other flows. What is net water-depth change?

120−80=40 mm increase, assuming uniform area and no inflow, runoff, infiltration or withdrawal.

A rooftop receives 0.05 m of rain over 100 m². Estimate water volume before losses.

V=depth×area=0.05×100=5 m³=5000 litres.

If a reservoir receives 600 m³ and loses 450 m³ during a day, what is net change?

600−450=150 m³ gain, assuming those are the only transfers.

Why can fertiliser runoff harm aquatic life?

Added nutrients may cause algal blooms; decomposition can consume dissolved oxygen, harming aquatic organisms.

What is the natural greenhouse effect?

Greenhouse gases absorb and emit infrared radiation, making Earth's surface warmer than it would be without them.

Why does melting reflective ice sometimes accelerate warming?

Less reflective ice exposes darker surfaces that absorb more sunlight, a positive ice-albedo feedback.

Revision checklist

I can explain earth as an interacting system and give an example.
I can explain atmosphere and give an example.
I can explain hydrosphere and give an example.
I can explain geosphere and give an example.
I can explain biosphere and give an example.
I can explain system boundaries and give an example.
I can explain solar energy and give an example.
I can explain earth's internal energy and give an example.
I can explain radiation and energy balance and give an example.
I can explain greenhouse effect and give an example.
I can explain weather and climate and give an example.
I can explain evaporation and transpiration and give an example.
I can explain condensation and clouds and give an example.
I can explain precipitation and give an example.
I can explain runoff, infiltration and groundwater and give an example.
I can explain water-cycle conservation and give an example.
I can explain carbon reservoirs and give an example.
I can explain photosynthesis and give an example.
I can explain respiration and give an example.
I can explain decomposition and give an example.
I can explain combustion and fossil fuels and give an example.
I can explain nitrogen cycle and give an example.
I can explain food chains and webs and give an example.
I can explain energy transfer in ecosystems and give an example.
I can explain trophic levels and give an example.
I can explain soil formation and give an example.
I can explain erosion and deposition and give an example.
I can explain human land-use change and give an example.
I can explain pollution and eutrophication and give an example.
I can explain climate change and feedbacks and give an example.
I can explain biodiversity and resilience and give an example.
I can explain sustainable resource use and give an example.
I can explain observing earth systems and give an example.
I can explain model limitations and give an example.

Official textbook reference

NCERT ePathshala — Exploration. Consult the prescribed textbook for exact official activities, diagrams and numbered exercises; this original guide is not a complete official answer key.