Class 9 Science Notes Chapter 14 (Chapter 14) – Examplar Problem (English) Book
Alright class, let's focus on Chapter 14: Natural Resources from your NCERT Science Exemplar book. This chapter is crucial not just for your school exams but also forms a fundamental part of the General Science section in many government exams. Pay close attention as we break down the key concepts.
Chapter 14: Natural Resources - Detailed Notes for Government Exam Preparation
1. Introduction: The Spheres of Earth
- Our planet Earth is the only one known to support life, primarily due to its resources and energy from the Sun.
- Resources on Earth are found in three major realms:
- Lithosphere: The solid, outer part of the Earth, consisting of the crust and upper mantle (land).
- Hydrosphere: All the water on Earth's surface (oceans, seas, lakes, rivers, groundwater, ice caps, glaciers). Covers about 75% of the Earth's surface.
- Atmosphere: The envelope of gases surrounding the Earth.
- Biosphere: The narrow zone where the Lithosphere, Hydrosphere, and Atmosphere interact and support life. It consists of:
- Biotic Components: Living organisms (plants, animals, microorganisms).
- Abiotic Components: Non-living factors (air, water, soil, sunlight, temperature).
2. The Breath of Life: Air
- Composition: Air is a mixture of gases:
- Nitrogen (N₂): ~78% (Essential for proteins, nucleic acids)
- Oxygen (O₂): ~21% (Essential for respiration, combustion)
- Carbon Dioxide (CO₂): ~0.03-0.04% (Used by plants for photosynthesis, greenhouse gas)
- Argon (Ar): ~0.9% (Inert gas)
- Other gases (Neon, Helium, Krypton, Xenon), Water Vapour, Dust Particles: Trace amounts.
- Role of the Atmosphere:
- Provides essential gases for life (O₂, CO₂, N₂).
- Regulates Earth's temperature, preventing extreme variations between day and night (due to air being a poor conductor of heat).
- Plays a key role in the water cycle.
- Protects life from harmful solar radiation (Ozone layer).
- Facilitates weather phenomena (wind, rain).
- Movement of Air (Wind): Caused by uneven heating of the Earth's surface.
- Land Breeze: Air moves from land to sea at night (land cools faster).
- Sea Breeze: Air moves from sea to land during the day (land heats faster).
- Global wind patterns are influenced by uneven heating between the equator and poles, and the Earth's rotation (Coriolis effect).
- Rain: Formed by the heating of water bodies, evaporation, formation of water vapour, rising of warm moist air, cooling at higher altitudes, condensation around nuclei (dust), formation of water droplets, coalescence, and precipitation.
- Air Pollution: Contamination of air by harmful substances (pollutants) that affect living organisms and the environment.
- Sources: Burning of fossil fuels (vehicles, industries, power plants), industrial emissions, agricultural activities (pesticides, fertilizers), mining, construction, waste decomposition, volcanic eruptions, forest fires.
- Major Pollutants: Oxides of Nitrogen (NOx), Oxides of Sulphur (SOx), Carbon Monoxide (CO), Carbon Dioxide (CO₂ - contributes to global warming), Particulate Matter (PM - soot, dust, smoke), Chlorofluorocarbons (CFCs).
- Effects: Respiratory diseases (asthma, bronchitis), cardiovascular problems, acid rain, smog formation, ozone layer depletion, global warming, reduced visibility, damage to vegetation and buildings.
- Lichens: Often used as bio-indicators of air pollution, particularly SO₂ pollution, as they are very sensitive and do not grow well in polluted areas.
- Acid Rain: Rainwater that becomes acidic (pH < 5.6) due to the dissolution of atmospheric pollutants like Sulphur Dioxide (SO₂) and Nitrogen Oxides (NOx), forming Sulphuric Acid (H₂SO₄) and Nitric Acid (HNO₃). Damages forests, aquatic life, buildings (especially marble - e.g., Taj Mahal), and soil fertility.
- Ozone Layer (O₃): Found in the Stratosphere. Protects Earth from harmful Ultraviolet (UV-B and UV-C) radiation from the sun.
- Formation: O₂ + UV → O + O ; O + O₂ → O₃
- Depletion: Caused mainly by Chlorofluorocarbons (CFCs) released from refrigerants, aerosols, solvents. Chlorine atoms from CFCs catalytically destroy ozone molecules.
- Ozone Hole: Significant thinning of the ozone layer, particularly over Antarctica.
- Effects of Depletion: Increased UV radiation reaching Earth, leading to skin cancer, cataracts, immune system suppression, damage to plants and aquatic ecosystems.
3. Water: A Wonder Liquid
- Importance: Essential for all life forms; universal solvent; regulates climate; habitat for aquatic organisms; used in agriculture, industry, domestic purposes.
- Distribution: Most water on Earth is saline (oceans, seas). Freshwater is limited (~2.5%), mostly locked in glaciers and ice caps. A small fraction is available as groundwater, lakes, and rivers.
- Water Pollution: Contamination of water bodies by harmful substances.
- Sources: Sewage (domestic waste), industrial effluents (chemicals, heavy metals), agricultural runoff (fertilizers, pesticides), thermal pollution (hot water from power plants), oil spills, solid waste dumping.
- Effects: Waterborne diseases (cholera, typhoid, dysentery), eutrophication (excess nutrients leading to algal blooms, oxygen depletion), bioaccumulation and biomagnification of toxins, harm to aquatic life, disruption of ecosystems, reduced dissolved oxygen (DO).
- Temperature Effect: Dissolved oxygen decreases as water temperature increases. Thermal pollution reduces DO, harming aquatic organisms.
- Water Scarcity: Increasing demand, pollution, and uneven distribution lead to water scarcity in many regions. Conservation and rainwater harvesting are crucial.
4. Soil: The Foundation of Life
- Formation (Pedogenesis): Slow process involving the breakdown of rocks (weathering) over thousands of years.
- Weathering: Physical (temperature changes, water freezing, wind, abrasion), Chemical (hydrolysis, oxidation, carbonation), and Biological (lichens, mosses, plant roots, burrowing animals).
- Parent Rock → Weathered Rock Material → Addition of Humus → Mature Soil.
- Composition: Mixture of rock particles (sand, silt, clay), humus (decomposed organic matter), water, air, and living organisms (bacteria, fungi, earthworms).
- Humus: Improves soil structure, water retention, aeration, and provides nutrients.
- Soil Texture: Determined by the relative proportion of sand, silt, and clay particles. Affects water holding capacity, drainage, and aeration.
- Soil Profile: Vertical section of soil showing different layers or horizons (O, A, B, C, R).
- Soil Erosion: Removal of the topsoil layer by agents like wind and water.
- Causes: Deforestation, overgrazing, improper farming techniques (tilling on slopes), construction activities, floods, strong winds.
- Effects: Loss of fertile topsoil, reduced agricultural productivity, sedimentation of water bodies, desertification, landslides.
- Prevention: Afforestation, contour ploughing, terrace farming, building check-dams, cover cropping, reducing overgrazing.
- Soil Pollution: Contamination of soil by harmful substances.
- Sources: Excessive use of pesticides and fertilizers, industrial waste, heavy metals, plastic waste, acid rain.
- Effects: Reduced soil fertility, harm to soil organisms, contamination of groundwater, entry of toxins into the food chain.
5. Biogeochemical Cycles
- The cyclical movement of essential elements (nutrients) between the biotic (living) and abiotic (non-living) components of the biosphere. Ensures the continuous availability of these elements.
- Water Cycle (Hydrological Cycle): Evaporation/Transpiration → Condensation → Precipitation → Runoff/Infiltration. Driven by solar energy.
- Nitrogen Cycle: Crucial for protein and nucleic acid synthesis.
- Atmospheric Nitrogen (N₂) is unusable by most organisms.
- Nitrogen Fixation: Conversion of N₂ into usable forms (ammonia, nitrates).
- Biological: By nitrogen-fixing bacteria (e.g., Rhizobium in root nodules of legumes, free-living bacteria like Azotobacter).
- Atmospheric: By lightning.
- Industrial: Haber process for fertilizers.
- Nitrification: Conversion of ammonia (NH₃) to nitrites (NO₂⁻) and then nitrates (NO₃⁻) by nitrifying bacteria (e.g., Nitrosomonas, Nitrobacter). Plants absorb nitrates.
- Assimilation: Incorporation of nitrates/ammonia into plant and animal tissues.
- Ammonification: Decomposition of dead organic matter and waste products back into ammonia by decomposers (bacteria, fungi).
- Denitrification: Conversion of nitrates back into gaseous Nitrogen (N₂) by denitrifying bacteria (e.g., Pseudomonas), returning it to the atmosphere.
- Carbon Cycle: Carbon is the backbone of organic molecules.
- Atmospheric CO₂: Reservoir of carbon.
- Photosynthesis: Plants take CO₂ from the atmosphere to make organic compounds.
- Respiration: Organisms release CO₂ back into the atmosphere.
- Decomposition: Decomposers release CO₂ from dead organic matter.
- Combustion: Burning of fossil fuels and wood releases large amounts of CO₂.
- Ocean Absorption: Oceans absorb and release CO₂. Carbon is also stored in carbonate rocks (limestone) and fossil fuels.
- Oxygen Cycle: Interlinked with the Carbon Cycle.
- Atmospheric O₂: Major reservoir.
- Photosynthesis: Releases O₂ as a byproduct.
- Respiration: Consumes O₂.
- Combustion: Consumes O₂.
- Oxide Formation: Oxygen combines with elements (e.g., iron rusting).
- Ozone Formation: O₂ is converted to O₃ in the stratosphere.
6. Greenhouse Effect
- Natural process where certain gases in the atmosphere (Greenhouse Gases - GHGs) trap heat, keeping the Earth warm enough for life.
- Major GHGs: Water Vapour (H₂O), Carbon Dioxide (CO₂), Methane (CH₄), Nitrous Oxide (N₂O), Ozone (O₃), CFCs.
- Enhanced Greenhouse Effect (Global Warming): Increase in the concentration of GHGs (especially CO₂ from burning fossil fuels, deforestation) traps more heat, leading to a rise in global average temperatures.
- Consequences: Climate change, melting glaciers and ice caps, sea-level rise, changes in precipitation patterns, more extreme weather events, impact on ecosystems and agriculture.
Multiple Choice Questions (MCQs)
-
Which of the following components constitute the biosphere?
a) Lithosphere and Atmosphere only
b) Hydrosphere and Atmosphere only
c) Lithosphere and Hydrosphere only
d) Lithosphere, Hydrosphere, and Atmosphere where life exists -
The primary reason for the movement of air (wind) is:
a) Rotation of the Earth
b) Uneven heating of the Earth's surface
c) Gravitational pull of the Moon
d) Differences in atmospheric pressure only -
Lichens are often used as bio-indicators because they are very sensitive to:
a) Carbon Monoxide pollution
b) Water pollution
c) Sulphur Dioxide pollution
d) Noise pollution -
The process of converting atmospheric nitrogen gas (N₂) into ammonia (NH₃) by bacteria like Rhizobium is called:
a) Nitrification
b) Denitrification
c) Nitrogen Fixation
d) Ammonification -
Acid rain is primarily caused by the atmospheric dissolution of:
a) Carbon Dioxide and Carbon Monoxide
b) Methane and Ozone
c) Oxides of Sulphur and Nitrogen
d) Chlorofluorocarbons (CFCs) -
Which of the following is NOT a major greenhouse gas?
a) Carbon Dioxide (CO₂)
b) Methane (CH₄)
c) Oxygen (O₂)
d) Nitrous Oxide (N₂O) -
The slow process of breakdown of rocks by physical, chemical, and biological agents leading to soil formation is known as:
a) Erosion
b) Sedimentation
c) Weathering
d) Decomposition -
Eutrophication in water bodies is often caused by:
a) High levels of dissolved oxygen
b) Introduction of heavy metals
c) Excessive input of nutrients like nitrates and phosphates
d) Thermal pollution -
The ozone layer, which protects us from harmful UV radiation, is mainly found in which layer of the atmosphere?
a) Troposphere
b) Stratosphere
c) Mesosphere
d) Thermosphere -
Which step in the carbon cycle involves the conversion of atmospheric CO₂ into organic compounds by plants?
a) Respiration
b) Combustion
c) Decomposition
d) Photosynthesis
Answer Key:
- d
- b
- c
- c
- c
- c
- c
- c
- b
- d
Study these notes thoroughly. Understand the processes, cycles, causes, and effects discussed. The Exemplar often tests the 'why' and 'how' behind these concepts. Good luck with your preparation!