NCERT Class 9 Science Earth as a System Energy Matter and Life Solutions
Short Intro
This chapter explains how Earth functions as an interconnected system involving energy flow, matter cycling, atmosphere, hydrosphere, lithosphere, and biosphere. Students learn about biogeochemical cycles, climate regulation, greenhouse gases, weather systems, and human impact on the environment through detailed explanations and solved questions.
Quick Information Box
| Topic | Details |
|---|---|
| Chapter Name | Earth as a System: Energy, Matter, and Life |
| Class | Grade 9 |
| Subject | Science |
| Main Topics | Earth Spheres, Climate, Biogeochemical Cycles |
| Energy Source | Sun |
| Important Cycles | Water, Carbon, Nitrogen, Oxygen |
Concepts Used (Topics Covered)
- Earth as an Interconnected System
- Atmosphere, Hydrosphere, Lithosphere and Biosphere
- Solar Radiation and Insolation
- Weather and Climate
- Wind Formation
- Ocean Currents
- Water Cycle
- Carbon Cycle
- Nitrogen Cycle
- Oxygen Cycle
- Greenhouse Effect
- Global Warming and Climate Change
- Eutrophication
- Deforestation
- Sustainable Development
Important Formulas
- Heat Transfer
Heat flows from hotter region to colder region. - Greenhouse Effect
Earth absorbs solar radiation and re-radiates infrared radiation trapped by greenhouse gases. - Water Cycle
Evaporation → Condensation → Precipitation → Runoff - Photosynthesis Equation
CO₂ + H₂O + Sunlight → Glucose + O₂ - Respiration Equation
Glucose + O₂ → CO₂ + H₂O + Energy
Questions & Step-by-step Solutions with Explanation
Q1. Role of Biogeochemical Cycles
Question:
Choose the correct role of biogeochemical cycles.
Options:
(i) Provide food directly
(ii) Recycle nutrients between biotic and abiotic components
(iii) Create new elements
(iv) Remove pollutants
Solution:
Biogeochemical cycles continuously recycle nutrients through living and non-living systems.
Answer:
(ii) Recycle essential nutrients between biotic and abiotic components
Q2. Cause of Earth’s Warming
Question:
Which process mainly warms Earth?
Solution:
Earth absorbs solar radiation and re-radiates heat energy which gets trapped by greenhouse gases.
Answer:
(iii) Earth’s surface absorbs solar radiation which is trapped by greenhouse gases.
Q3. Climate Change and Water Cycle
Solution:
Climate change affects evaporation, rainfall, and storms.
Examples:
- Higher temperatures increase evaporation.
- Some regions experience floods.
- Other regions face droughts.
- Glaciers melt rapidly.
Answer:
Climate change disturbs the balance of the water cycle.
Q4. Effect of Albedo on Climate
Solution:
Albedo is the reflecting power of a surface.
- Ice and snow have high albedo and reflect sunlight.
- Dark surfaces absorb more heat.
Higher albedo lowers temperature while lower albedo increases warming.
Q5. Mountain and Valley Breezes
Solution:
Valley Breeze:
During day, mountain slopes heat quickly and warm air rises upward.
Mountain Breeze:
At night, mountain slopes cool rapidly and cool air flows downward.
Grass vs Rocky Mountain:
Grass-covered mountain remains cooler due to vegetation and moisture.
Rocky mountain heats faster and produces warmer breeze.
Q6. Atmospheric Layer Responsible for Weather
Solution:
Most weather phenomena occur in the troposphere.
Reason:
- Contains most water vapour
- Uneven heating causes winds, rainfall and storms
Answer:
Troposphere
Q7. Nitrogen Cycle
Solution:
Main Steps:
- Nitrogen fixation by bacteria
- Conversion into nitrates
- Absorption by plants
- Transfer to animals
- Decomposition
- Return to atmosphere
If Nitrogen Was Not Cycled:
- Plants could not make proteins.
- Food chains would collapse.
- Life would become impossible.
Q8. Effects of Deforestation
Solution:
Deforestation reduces:
- Photosynthesis
- Oxygen production
It increases:
- Carbon dioxide concentration
- Global warming
- Soil erosion
- Biodiversity loss
Answer:
Deforestation disturbs oxygen and carbon cycles severely.
Q9. Carbon Cycle Diagram Explanation
Solution:
- Plants absorb CO₂ during photosynthesis.
- Animals eat plants.
- Respiration releases CO₂.
- Dead organisms decompose.
- Combustion of fuels releases CO₂ back into atmosphere.
Q10. Why Excess CO₂ is Harmful
Solution:
Although plants need CO₂ for photosynthesis, excess CO₂ traps more heat in atmosphere.
This causes:
- Global warming
- Climate change
- Rising sea levels
Answer:
Excess CO₂ intensifies greenhouse effect.
Q11. Heat Loss from Earth
Solution:
Earth loses heat by infrared radiation into space.
Significance:
This prevents Earth from becoming excessively hot and maintains thermal balance.
Q12. If Earth Were Flat
Solution:
Solar radiation distribution would change greatly.
- Equal day length would occur everywhere.
- Temperature variation between equator and poles would reduce.
- Climate patterns would differ significantly.
Q13. Effect of Rising Atmospheric Temperature
Cryosphere:
- Melting glaciers and polar ice
Hydrosphere:
- Rising sea level
- Increased evaporation
Biosphere:
- Habitat destruction
- Species extinction
Q14. Importance of Atmosphere
Solution:
Atmosphere:
- Traps suitable heat
- Blocks harmful radiation
- Maintains temperature balance
- Supports life processes
Answer:
Atmosphere makes Earth suitable for life.
Q15. Interrelationship Between Earth’s Spheres
Solution:
The four spheres interact continuously.
Example:
- Water evaporates from oceans (hydrosphere)
- Forms clouds in atmosphere
- Falls on land (lithosphere)
- Supports plants and animals (biosphere)
This balance sustains life on Earth.
Common Mistakes
- Confusing weather with climate
- Forgetting steps of biogeochemical cycles
- Mixing greenhouse effect with ozone depletion
- Ignoring role of atmosphere in heat balance
- Writing incomplete carbon cycle steps
Exam Tips
- Learn all cycles using flow diagrams.
- Revise greenhouse effect carefully.
- Practice definitions of atmosphere layers.
- Draw labelled diagrams neatly.
- Remember causes and effects of climate change.
Practice MCQs
1. Main source of Earth’s energy:
A. Moon
B. Volcanoes
C. Sun
D. Oceans
Answer:
C. Sun
2. Weather phenomena mainly occur in:
A. Stratosphere
B. Mesosphere
C. Troposphere
D. Thermosphere
Answer:
C. Troposphere
3. Which gas mainly causes greenhouse effect?
A. Oxygen
B. Nitrogen
C. Carbon dioxide
D. Helium
Answer:
C. Carbon dioxide
4. Excess nutrients in water bodies cause:
A. Condensation
B. Eutrophication
C. Respiration
D. Weathering
Answer:
B. Eutrophication
5. Plants release oxygen during:
A. Respiration
B. Combustion
C. Photosynthesis
D. Decomposition
Answer:
C. Photosynthesis
FAQ Section
Q1. What are biogeochemical cycles?
They are natural cycles that recycle matter between living and non-living components.
Q2. What is the greenhouse effect?
Trapping of heat by greenhouse gases in atmosphere.
Q3. What is eutrophication?
Excessive algal growth in water bodies due to nutrient pollution.
Q4. Why is the atmosphere important?
It regulates temperature and supports life.
Q5. What causes climate change?
Mainly increased greenhouse gases from human activities.
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