Earth As a System Energy Matter and Life — Class 9 Science NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 9 Science chapter "Earth As a System Energy Matter and Life" — 9 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 9 Science chapter "Earth As a System Energy Matter and Life" — 9 important questions with detailed answers…
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NCERT Solutions for Class 9 Science — Earth As a System Energy Matter and Life. Step-by-step answers to all 9 textbook questions from this chapter, written for CBSE board preparation and free to use.
Earth As a System Energy Matter and Life — All 9 Questions Solved
Q1. What are natural resources? Classify and explain air, water, and soil.
Natural resources = Materials/energy from nature used by organisms.
Classification: Renewable (replenished naturally) and Non-renewable (finite supply).
AIR: Mixture of gases (N₂ 78%, O₂ 21%, Ar 0.9%, CO₂ 0.04%, other gases)
• Renewable resource
• Provides oxygen for respiration
• Used in combustion, photosynthesis
WATER: Essential liquid covering 71% of Earth
• Renewable (through water cycle)
• Solvent, participant in biochemical reactions
• Habitats for aquatic organisms
SOIL: Weathered rock + organic matter + organisms
• Renewable (slowly) resource
• Medium for plant growth
• Supports biodiversity
• Nutrient cycling occurs in soil
Q2. Explain the water cycle (hydrological cycle) and its stages.
Water cycle = Continuous movement of water between atmosphere, hydrosphere, and lithosphere.
Stages:
(1) Evaporation: Water from surface (ocean, lake, river, soil) → Water vapor (due to solar heat)
(2) Transpiration: Water from plants → Water vapor (through leaves)
(3) Condensation: Water vapor → Liquid water droplets (in atmosphere, forms clouds)
(4) Precipitation: Water falls as rain, snow, hail, sleet
(5) Infiltration: Water soaks into soil (groundwater)
(6) Percolation: Water moves through soil layers (recharges aquifers)
(7) Collection: Water accumulates in oceans, lakes, rivers
(8) Runoff: Water flows from land to water bodies
Significance: (1) Distributes water globally
(2) Transports nutrients
(3) Regulates climate
(4) Sustains life
Q3. Explain the nitrogen cycle and its importance.
Nitrogen cycle = Movement of nitrogen between atmosphere, soil, organisms, and back.
Stages:
(1) Nitrogen fixation: Atmospheric N₂ → Nitrates/Ammonia (by nitrogen-fixing bacteria)
• Bacteria in soil, root nodules of legumes
• Lightning also fixes nitrogen
(2) Nitrification: Ammonia (NH₃) → Nitrites (NO₂⁻) → Nitrates (NO₃⁻)
• By nitrifying bacteria (in soil)
(3) Assimilation: Plants absorb nitrates → Plant proteins
• Animals eat plants → Animal proteins
(4) Ammonification: Dead organisms, waste → Ammonia (by decomposers)
(5) Denitrification: Nitrates → Atmospheric N₂ (by denitrifying bacteria)
Importance:
• Nitrogen is essential component of proteins and nucleic acids
• Cycle replenishes soil nitrogen
• Agricultural importance (legumes enrich soil)
Q4. Explain the carbon cycle and its stages.
Carbon cycle = Movement of carbon between atmosphere, organisms, and geosphere.
Stages:
(1) Carbon fixation: Atmospheric CO₂ + H₂O → Glucose (by photosynthesis in plants)
(2) Respiration: Organisms oxidize glucose → CO₂ + H₂O (returns to atmosphere)
(3) Consumption: Animals eat plants/other animals (carbon in food)
(4) Decomposition: Dead organisms → CO₂ (by decomposers)
(5) Fossil fuel combustion: Fossil fuels → CO₂ (coal, oil, natural gas burning)
(6) Sedimentation: Some carbon settles as sediment → Fossil fuels (over millions of years)
Key processes:
• Green plants: Producers (fix CO₂)
• Animals: Consumers (respire, release CO₂)
• Decomposers: Decompose organic matter (release CO₂)
Importance: (1) Maintains atmospheric CO₂ balance
(2) Sustains food chains
(3) Regulates climate
Q5. Explain the oxygen cycle and its significance.
Oxygen cycle = Movement of oxygen between atmosphere, organisms, and compounds.
Stages:
(1) Photosynthesis: Plants release O₂ (H₂O → O₂ + H⁺)
(2) Respiration: Organisms use O₂ (Glucose + O₂ → CO₂ + H₂O)
(3) Combustion: Fossil fuels burn (consume O₂, release CO₂)
(4) Decomposition: Decomposers use O₂
(5) Oxidation-reduction reactions: In soil and water
Key processes:
• Photosynthesis: Main source of atmospheric O₂
• Respiration: Major consumer of O₂
• Combustion: Increases O₂ consumption
Significance:
(1) Essential for aerobic respiration (energy production)
(2) Forms protective ozone layer (O₃)
(3) Maintains atmospheric O₂ (~21%)
(4) Sustains all aerobic life
(5) Involved in weathering of rocks
Q6. What is the greenhouse effect? How do greenhouse gases cause global warming?
Greenhouse effect = Phenomenon where atmospheric gases trap heat, warming Earth's surface.
Greenhouse gases: CO₂, CH₄ (methane), N₂O (nitrous oxide), water vapor, CFCs
Mechanism:
(1) Sunlight enters atmosphere and reaches Earth's surface
(2) Surface absorbs heat and radiates infrared radiation (heat)
(3) Greenhouse gases absorb infrared radiation
(4) Heat radiates back to surface and space
(5) More gases → More heat trapped → Surface temperature increases
Causes of increased greenhouse effect (Global warming):
• Increased CO₂: Fossil fuel combustion, deforestation
• Methane: Cattle farming, landfills
• CFCs: Refrigerants, aerosols
Consequences:
(1) Rising average global temperature
(2) Melting ice caps and glaciers
(3) Rising sea levels
(4) Climate change, extreme weather events
Q7. What is the ozone layer? How do CFCs deplete ozone? What are consequences?
Ozone layer = Layer of O₃ in stratosphere (15-35 km altitude) protecting from UV radiation.
Formation: O₂ + UV light → Oxygen atoms; O + O₂ → O₃
Ozone depletion mechanism:
(1) CFCs (Chlorofluorocarbons) released from refrigerators, air conditioners, aerosols
(2) CFCs rise to stratosphere
(3) UV light breaks CFC: CFC → Cl atoms
(4) Chlorine reacts with ozone: Cl + O₃ → ClO + O₂
(5) One Cl can destroy 100,000 O₃ molecules
Consequences of ozone depletion:
(1) Increased UV radiation reaches Earth
(2) Skin cancer and cataracts in humans
(3) Immune system suppression
(4) Damage to phytoplankton and crops
(5) Ecological disruption
Solutions: Ban CFCs, use ozone-friendly alternatives (HFCs)
Q8. What is the difference between renewable and non-renewable resources? Give five examples of each.
Renewable resources = Resources replenished by nature within human timescale; can be used sustainably.
Non-renewable resources = Resources that cannot be replenished; finite supply; once used, cannot be replaced in human timescale.
Renewable resources (5 examples):
(1) Water: Replenished by water cycle
(2) Solar energy: Continuous radiation from sun
(3) Wind energy: Continuous wind patterns
(4) Forests: Trees can be replanted and regrow
(5) Agricultural crops: Harvested and replanted annually
Non-renewable resources (5 examples):
(1) Coal: Fossil fuel, takes millions of years to form
(2) Oil/Petroleum: Fossil fuel, finite supply
(3) Natural gas: Fossil fuel, limited reserves
(4) Minerals: Ore deposits, finite and non-replenishable
(5) Uranium: Radioactive, limited reserves for nuclear energy
Sustainability: Use renewable resources; conserve non-renewable resources
Q9. Explain biodiversity and its importance. What factors affect biodiversity?
Biodiversity = Variety of all living organisms on Earth; includes genetic, species, and ecosystem diversity.
Importance of biodiversity:
(1) Ecosystem stability: More diverse ecosystems are more stable and resilient
(2) Food webs: Maintains food chains and nutrients cycling
(3) Medicines: Many drugs derived from plants and animals
(4) Agriculture: Genetic diversity ensures crop productivity
(5) Climate regulation: Forests, wetlands regulate temperature and rainfall
(6) Pollination: Insects pollinate crops and wild plants
(7) Economic: Tourism, fisheries, forestry depend on biodiversity
Factors affecting biodiversity:
(1) Habitat destruction: Deforestation, urbanization reduce habitats
(2) Climate change: Alters temperature, rainfall patterns
(3) Pollution: Contaminants harm organisms
(4) Overexploitation: Overhunting, overfishing reduces populations
(5) Invasive species: Non-native species disrupt ecosystems
(6) Diseases: Pathogen outbreaks affect populations
Conservation: Protected areas, species preservation, sustainable practices
Earth As a System Energy Matter and Life — Practice MCQs with Answers
Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.
MCQ 1. Which of Earth's spheres includes all living organisms?
- A. Lithosphere
- B. Hydrosphere
- C. Atmosphere
- D. Biosphere
Answer: D. Biosphere — The Biosphere is the part of Earth where life exists, encompassing parts of the lithosphere, hydrosphere, and atmosphere.
MCQ 2. What is the primary source of energy for most ecosystems on Earth?
- A. Geothermal energy
- B. Solar energy
- C. Chemical energy
- D. Wind energy
Answer: B. Solar energy — Solar energy is the ultimate source of energy for nearly all life on Earth, primarily through photosynthesis carried out by producers.
MCQ 3. Which process converts atmospheric carbon dioxide into organic compounds by plants?
- A. Respiration
- B. Decomposition
- C. Photosynthesis
- D. Combustion
Answer: C. Photosynthesis — Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water.
MCQ 4. The continuous movement of water on, above, and below the surface of the Earth is known as the:
- A. Carbon cycle
- B. Nitrogen cycle
- C. Water cycle
- D. Oxygen cycle
Answer: C. Water cycle — The water cycle (or hydrological cycle) describes the continuous movement of water within the Earth's system.
MCQ 5. Which layer of the atmosphere protects Earth from harmful ultraviolet (UV) radiation?
- A. Troposphere
- B. Stratosphere
- C. Mesosphere
- D. Thermosphere
Answer: B. Stratosphere — The ozone layer, located in the stratosphere, absorbs most of the Sun's harmful ultraviolet radiation, preventing it from reaching the Earth's surface.
MCQ 6. What is the role of decomposers in an ecosystem?
- A. To produce food through photosynthesis
- B. To consume producers directly
- C. To break down dead organic matter and return nutrients to the soil
- D. To regulate atmospheric temperature
Answer: C. To break down dead organic matter and return nutrients to the soil — Decomposers, like bacteria and fungi, play a crucial role by breaking down dead organisms and waste products, recycling essential nutrients back into the ecosystem.
MCQ 7. Which of the following human activities significantly contributes to the increase of carbon dioxide in the atmosphere?
- A. Afforestation
- B. Using public transport
- C. Burning of fossil fuels
- D. Composting organic waste
Answer: C. Burning of fossil fuels — The combustion of fossil fuels (coal, oil, natural gas) for energy releases large amounts of stored carbon into the atmosphere as carbon dioxide.
MCQ 8. Nitrogen gas from the atmosphere is converted into usable forms by certain bacteria in a process called:
- A. Denitrification
- B. Nitrification
- C. Ammonification
- D. Nitrogen fixation
Answer: D. Nitrogen fixation — Nitrogen fixation is the process where atmospheric nitrogen (N2) is converted into ammonia or other nitrogenous compounds by microorganisms, making it available for plants.
MCQ 9. What happens to most of the solar energy that reaches Earth's atmosphere?
- A. It is entirely absorbed by the land and oceans.
- B. It is reflected back into space.
- C. It is completely used by plants for photosynthesis.
- D. It warms only the upper atmosphere.
Answer: B. It is reflected back into space. — About 70% of the incoming solar radiation is absorbed by the Earth's surface and atmosphere, while the rest is reflected back to space.
MCQ 10. The interaction between the lithosphere and the hydrosphere can be observed in which of the following phenomena?
- A. Cloud formation
- B. Ocean tides
- C. Weathering and erosion by rivers
- D. Volcanic eruptions
Answer: C. Weathering and erosion by rivers — Weathering of rocks and erosion of soil by flowing water (rivers, glaciers, waves) are prime examples of the interaction between the solid Earth (lithosphere) and water (hydrosphere).
MCQ 11. Which gas is primarily responsible for the greenhouse effect on Earth?
- A. Oxygen
- B. Nitrogen
- C. Argon
- D. Carbon dioxide
Answer: D. Carbon dioxide — Carbon dioxide is the most significant greenhouse gas in the atmosphere, trapping heat and contributing to the greenhouse effect.
MCQ 12. If deforestation occurs in a large area, how would it primarily impact the local water cycle?
- A. Increased precipitation
- B. Decreased evaporation from the ground
- C. Increased runoff and reduced transpiration
- D. No significant impact
Answer: C. Increased runoff and reduced transpiration — Deforestation reduces transpiration by plants, leading to less moisture released into the atmosphere, and increases surface runoff as less water is absorbed by vegetation.
MCQ 13. Which of the following is an example of an ecosystem?
- A. A single oak tree
- B. All the deer in a forest
- C. A pond with all its living organisms and non-living factors
- D. The global population of humans
Answer: C. A pond with all its living organisms and non-living factors — An ecosystem comprises all the living organisms (biotic components) in a particular area, as well as the non-living physical components (abiotic components) of the environment, such as water, soil, and sunlight, interacting as a system.
MCQ 14. The process by which water vapor in the atmosphere cools and changes into liquid water droplets, forming clouds, is called:
- A. Evaporation
- B. Condensation
- C. Precipitation
- D. Transpiration
Answer: B. Condensation — Condensation is the process where water vapor loses heat and changes into liquid water, forming clouds and fog.
MCQ 15. How do ocean currents play a role in Earth's energy balance?
- A. They absorb all incoming solar radiation.
- B. They only affect local weather patterns.
- C. They redistribute heat from the equator towards the poles and vice-versa.
- D. They are solely responsible for global warming.
Answer: C. They redistribute heat from the equator towards the poles and vice-versa. — Ocean currents are crucial in distributing heat energy around the globe, moving warm water from the tropics to higher latitudes and cold water back towards the equator, moderating regional climates.
MCQ 16. Which of these is NOT a component of the Earth's 'life support system' as understood in the 'Earth as a System' concept?
- A. Atmosphere
- B. Biosphere
- C. Solar system
- D. Hydrosphere
Answer: C. Solar system — The 'Earth as a System' concept typically refers to the interacting spheres of Earth (atmosphere, biosphere, hydrosphere, lithosphere). The solar system is a much larger astronomical system.
MCQ 17. The cycling of matter, such as carbon, nitrogen, and water, through the Earth's spheres is primarily driven by:
- A. Tectonic plate movements
- B. Internal heat of the Earth
- C. Solar energy and gravity
- D. Magnetic field variations
Answer: C. Solar energy and gravity — Solar energy provides the power for processes like evaporation in the water cycle and photosynthesis in the carbon cycle, while gravity influences precipitation and water flow. Together, they drive biogeochemical cycles.
MCQ 18. What is the long-term consequence of excessive use of fertilizers containing nitrogen and phosphorus in agricultural fields?
- A. Increased soil fertility indefinitely
- B. Decreased crop yields due to toxicity
- C. Eutrophication of nearby water bodies
- D. Enhanced ozone layer formation
Answer: C. Eutrophication of nearby water bodies — Excessive fertilizers can run off into rivers and lakes, leading to eutrophication, a process where nutrient overload causes algal blooms and subsequent oxygen depletion, harming aquatic life.
MCQ 19. Which statement best describes the 'system' aspect of Earth?
- A. Earth is a collection of independent components.
- B. Earth's components interact and influence each other in complex ways.
- C. Earth's system is entirely closed to energy and matter exchange.
- D. Earth's atmosphere is the only active component of the system.
Answer: B. Earth's components interact and influence each other in complex ways. — The 'Earth as a System' concept emphasizes that Earth's various spheres (atmosphere, hydrosphere, lithosphere, biosphere) are interconnected and constantly interact, forming a dynamic and complex system.
MCQ 20. When an organism dies, its carbon is returned to the environment primarily through which process?
- A. Photosynthesis
- B. Respiration
- C. Combustion
- D. Decomposition
Answer: D. Decomposition — Decomposition by bacteria and fungi breaks down dead organic matter, releasing carbon back into the soil, water, and atmosphere.
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.