Class 9 Science Notes Chapter 14 (Natural Resources) – Science Book
Alright class, let's focus on Chapter 14: Natural Resources. This is a crucial chapter, not just for your exams but also for understanding the world around us and its challenges. Many government exams draw questions from fundamental concepts like these.
Chapter 14: Natural Resources - Detailed Notes for Exam Preparation
1. What are Natural Resources?
- Resources available from nature that support life and fulfill human needs.
- Examples: Air, water, soil, minerals, forests, wildlife, fossil fuels (coal, petroleum).
- Earth's resources are found in its major spheres:
- Lithosphere: The solid outer part of the Earth (land, soil, rocks).
- Hydrosphere: All the water on Earth (oceans, rivers, lakes, groundwater, ice caps, water vapour).
- Atmosphere: The envelope of gases surrounding the Earth.
- Biosphere: The zone where life exists, encompassing parts of the lithosphere, hydrosphere, and atmosphere. It's the interaction zone of living (biotic) and non-living (abiotic) components.
2. The Breath of Life: Air (Atmosphere)
- Composition: Primarily Nitrogen (approx. 78%), Oxygen (approx. 21%), Argon (approx. 0.9%), Carbon Dioxide (approx. 0.03-0.04%), trace gases, water vapour, and dust particles.
- Role of the Atmosphere:
- Provides essential gases (O2 for respiration, CO2 for photosynthesis, N2 for protein synthesis via fixation).
- Acts as a blanket, moderating Earth's temperature (prevents extreme heat during the day and extreme cold at night).
- Plays a key role in climate control.
- Movement of Air (Winds):
- Caused by uneven heating of the Earth's surface (land heats/cools faster than water).
- Creates regions of high and low pressure. Air moves from high-pressure areas to low-pressure areas, resulting in wind.
- Factors influencing wind patterns: Uneven heating between equator and poles, rotation of the Earth (Coriolis effect - though not detailed in NCERT 9th, good to be aware), local geographical features (mountains, valleys).
- Sea breeze (daytime: sea to land) and Land breeze (night-time: land to sea).
- Rain:
- Formation: Solar heat evaporates water from water bodies -> water vapour rises -> cools at higher altitudes -> condenses around dust particles (condensation nuclei) forming tiny droplets -> droplets coalesce to form larger drops -> fall as rain (precipitation). Snow or hail forms if temperatures are very low.
- Air Pollution:
- Contamination of air by harmful substances.
- Sources: Combustion of fossil fuels (vehicles, industries, power plants), industrial emissions, agricultural activities (burning stubble), mining, waste burning.
- Pollutants: Suspended Particulate Matter (SPM), Oxides of Sulphur (SOx), Oxides of Nitrogen (NOx), Carbon Monoxide (CO), Carbon Dioxide (CO2 - contributes to global warming), Chlorofluorocarbons (CFCs), smoke, dust.
- Effects: Respiratory diseases (asthma, bronchitis), acid rain (damage to buildings, soil, water bodies, crops), smog (reduced visibility, health issues), global warming (due to increased greenhouse gases like CO2), ozone layer depletion (due to CFCs).
- Lichens: Often act as bio-indicators of air pollution, especially SO2 levels, as they are sensitive and don't grow well in polluted areas.
3. Water: A Wonder Liquid (Hydrosphere)
- Importance: Essential for all life forms (cellular processes, transport, temperature regulation), habitat for aquatic organisms, used in agriculture, industry, domestic purposes.
- Distribution: Most water is saline (oceans, seas). Freshwater is limited (found in ice caps/glaciers, groundwater, rivers, lakes, atmosphere). Availability of usable freshwater varies greatly.
- Water Pollution:
- Contamination of water bodies.
- Sources:
- Sewage (untreated domestic waste containing pathogens).
- Industrial effluents (toxic chemicals, heavy metals).
- Agricultural runoff (excess fertilizers causing eutrophication, pesticides harming aquatic life).
- Thermal pollution (release of hot water from power plants/industries, reducing dissolved oxygen).
- Oil spills.
- Effects: Water-borne diseases (cholera, typhoid, dysentery), Eutrophication (excess nutrients lead to algal bloom, oxygen depletion, death of aquatic animals), Biomagnification (accumulation of toxins in food chains), loss of aquatic biodiversity, reduced dissolved oxygen.
4. Soil: The Resource from Land (Lithosphere)
- Definition: The uppermost layer of the Earth's crust, consisting of a mixture of weathered rock particles, minerals, organic matter (humus), water, air, and living organisms.
- Formation of Soil (Pedogenesis):
- A slow process involving weathering of parent rock.
- Weathering: Breakdown of rocks by:
- Physical Weathering: Temperature changes (expansion/contraction), water (freezing/thawing, abrasion), wind (abrasion).
- Chemical Weathering: Hydrolysis, oxidation, carbonation, acid rain.
- Biological Weathering: Plant roots growing into cracks, lichens producing acids, burrowing animals.
- Factors Influencing Soil Formation: Parent rock (determines mineral content), Climate (temperature, rainfall affect weathering rate), Topography (slope affects erosion and water retention), Biological activity (organisms contribute humus, mix soil), Time.
- Composition: Minerals (from parent rock), Organic Matter/Humus (decomposed plant/animal remains, improves fertility and structure), Water, Air (in pore spaces), Soil organisms (bacteria, fungi, earthworms, insects).
- Soil Pollution:
- Contamination by harmful substances.
- Sources: Excessive use of pesticides and fertilizers, industrial waste dumping, plastic waste, acid rain.
- Effects: Reduced soil fertility, harm to soil microorganisms, contamination of groundwater, entry of toxins into the food chain.
- Soil Erosion:
- Removal of the fertile topsoil by agents like wind and water.
- Causes: Deforestation, overgrazing, improper farming techniques (e.g., tilling on slopes), leaving land bare, strong winds, heavy rainfall.
- Effects: Loss of fertility, reduced agricultural productivity, silting of rivers and reservoirs, desertification.
- Prevention: Afforestation/Reforestation, cover crops, contour ploughing, terracing (on slopes), check dams, mulching, reducing overgrazing.
5. Biogeochemical Cycles
- The cyclic movement of essential nutrients (like water, carbon, nitrogen, oxygen) between the biotic (living) and abiotic (non-living) components of the biosphere. These cycles ensure the continuous availability of these elements.
- Water Cycle: (Covered partly under 'Rain') Evaporation/Transpiration -> Condensation -> Precipitation -> Runoff/Infiltration (Groundwater).
- Nitrogen Cycle:
- Nitrogen (N2) gas (78% of air) is unusable directly by most organisms.
- Nitrogen Fixation: Conversion of atmospheric N2 into usable compounds (ammonia, nitrates).
- Biological: By nitrogen-fixing bacteria (e.g., Rhizobium in root nodules of legumes, free-living bacteria like Azotobacter).
- Atmospheric: By lightning (high energy converts N2 to oxides of nitrogen).
- Industrial: Haber process for making fertilizers.
- Nitrification: Conversion of ammonia (NH3) to nitrites (NO2-) and then nitrates (NO3-) by nitrifying bacteria.
- Assimilation: Uptake of nitrates or ammonium ions by plants to make proteins, nucleic acids. Nitrogen then passes to animals when they eat plants.
- Ammonification: Decomposition of dead organic matter (plants, animals, waste) by bacteria and fungi, releasing ammonia (NH3).
- Denitrification: Conversion of nitrates (NO3-) back to nitrogen gas (N2) by denitrifying bacteria, returning it to the atmosphere.
- Carbon Cycle:
- Carbon is the basis of all organic molecules.
- Processes:
- Photosynthesis: Plants take CO2 from the atmosphere to make glucose.
- Respiration: Organisms (plants, animals, microbes) release CO2 during energy production.
- Combustion: Burning of fossil fuels and organic matter releases CO2.
- Decomposition: Microbes break down dead organic matter, releasing CO2.
- Oceanic exchange: CO2 dissolves in water; marine organisms use carbonates for shells/skeletons.
- Human Impact: Burning fossil fuels has significantly increased atmospheric CO2, leading to the enhanced Greenhouse Effect and Global Warming.
- Oxygen Cycle:
- Closely linked to the Carbon Cycle.
- Release: Primarily through photosynthesis by plants and phytoplankton.
- Consumption: Respiration by organisms, combustion (burning), decomposition, formation of oxides (e.g., rust, oxides of nitrogen).
6. The Ozone Layer
- Ozone (O3): A molecule made of three oxygen atoms. It's poisonous at ground level but vital in the stratosphere.
- Location: Concentrated in the Stratosphere (upper atmosphere).
- Function: Absorbs most of the harmful Ultraviolet (UV-B and UV-C) radiation from the sun, protecting life on Earth.
- Ozone Depletion: Thinning of the ozone layer, particularly over Antarctica (the "ozone hole").
- Cause: Release of human-made chemicals, primarily Chlorofluorocarbons (CFCs), previously used in refrigerators, air conditioners, aerosols. CFCs release chlorine atoms in the stratosphere, which catalytically destroy ozone molecules.
- Effects of increased UV radiation: Increased risk of skin cancer, cataracts, immune system suppression, damage to plants and phytoplankton (base of aquatic food webs).
- Mitigation: International agreements like the Montreal Protocol have phased out CFC production and use, leading to signs of ozone layer recovery.
Key Takeaway: Natural resources are finite and interconnected. Human activities significantly impact these resources and cycles. Sustainable management and conservation are essential for the well-being of the planet and future generations.
Multiple Choice Questions (MCQs)
-
Which of the following components constitutes the largest percentage of the Earth's atmosphere by volume?
a) Oxygen
b) Carbon Dioxide
c) Nitrogen
d) Argon -
The process by which water vapour changes into liquid water droplets, forming clouds, is called:
a) Evaporation
b) Precipitation
c) Transpiration
d) Condensation -
Acid rain is primarily caused by the atmospheric pollution of:
a) Carbon Monoxide and Carbon Dioxide
b) Oxides of Sulphur and Nitrogen
c) Methane and CFCs
d) Suspended Particulate Matter -
Rhizobium bacteria, found in the root nodules of leguminous plants, play a crucial role in which biogeochemical cycle?
a) Carbon Cycle
b) Water Cycle
c) Nitrogen Cycle
d) Oxygen Cycle -
The breakdown of rocks by changes in temperature, wind, water, and ice is known as:
a) Soil erosion
b) Decomposition
c) Physical weathering
d) Eutrophication -
The phenomenon where excessive nutrients in a water body lead to dense growth of plant life (like algal blooms) and death of animal life from lack of oxygen is called:
a) Biomagnification
b) Eutrophication
c) Denitrification
d) Ammonification -
Which of the following is the main human activity contributing to the enhanced greenhouse effect and global warming?
a) Deforestation
b) Use of CFCs
c) Burning of fossil fuels
d) Use of nitrogenous fertilizers -
The vital layer in the stratosphere that protects life on Earth from harmful ultraviolet radiation is the:
a) Troposphere layer
b) Mesosphere layer
c) Ozone layer
d) Ionosphere layer -
Which of the following methods helps prevent soil erosion on sloped land?
a) Overgrazing
b) Deforestation
c) Terracing
d) Monoculture farming -
The term 'Biosphere' refers to:
a) The gaseous envelope surrounding the Earth.
b) All the water bodies on Earth's surface.
c) The solid, rocky outer part of the Earth.
d) The zone of Earth where life exists, integrating parts of air, water, and land.
Answer Key for MCQs:
- c) Nitrogen
- d) Condensation
- b) Oxides of Sulphur and Nitrogen
- c) Nitrogen Cycle
- c) Physical weathering
- b) Eutrophication
- c) Burning of fossil fuels
- c) Ozone layer
- c) Terracing
- d) The zone of Earth where life exists, integrating parts of air, water, and land.
Study these notes thoroughly. Remember to connect the concepts – how air pollution affects water (acid rain), how deforestation affects soil erosion and the water cycle, and how human activities impact all these natural cycles. Good luck with your preparation!