CBSE Class 9 Science Natural Resources Sure Shot Questions Set 03

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ASSIGNMENT QUESTIONS SET - 3
CHAPTER - 14
NATURAL RESOURCES

 

1. What is soil erosion ? List two activities which cause soil erosion. [2 Marks]

Answer:
1. The removal of top fertile layer of soil by wind or water is known as soil erosion.
2. Deforestation and overgrazing by cattle are two major human activities that cause soil erosion.

Teacher's Note:
a) Soil erosion reduces soil fertility by stripping away nutrient-rich topsoil.
b) Roots of plants bind soil particles together, preventing this displacement.
c) Human intervention heavily accelerates natural erosion rates.

 

2. What is green house effect ? How is it caused ? [2 Marks]

Answer:
1. The greenhouse effect is the trapping of the sun's warmth in a planet's lower atmosphere due to the greater transparency of the atmosphere to visible radiation from the sun than to infrared radiation emitted from the planet's surface.
2. It is caused by the accumulation of greenhouse gases such as carbon dioxide, methane, and water vapour in the atmosphere.

Teacher's Note:
a) This natural phenomenon keeps Earth warm enough to sustain life.
b) Excessive greenhouse gases from human activities cause global warming.

 

3. Many municipal Corporations are trying water harvesting to improve the availability of water. Give reason. [2 Marks]

Answer:
1. Rapid urbanisation has covered soil with concrete, reducing the seepage of rainwater into the ground.
2. Water harvesting helps recharge groundwater levels, ensuring sustainable water availability during dry periods.

Teacher's Note:
a) Groundwater depletion is a severe crisis in urban areas.
b) Water harvesting captures rainwater effectively for future utility.

 

4. Rain water sometimes contains traces of acid. Why ? Explain in brief. [2 Marks]

Answer:
1. Pollutants like sulphur dioxide and nitrogen dioxide are released into the atmosphere from burning fossil fuels.
2. These gases dissolve in rainwater to form weak sulphuric acid and nitric acid, leading to acid rain.

Teacher's Note:
a) Fossil fuel combustion is the primary culprit behind acidic emissions.
b) Acid rain harms aquatic ecosystems and damages monuments.

 

5. Define the term 'Smog'. Name two types of diseases caused by regularly breathing the polluted air. [2 Marks]

Answer:
1. Smog is a type of air pollution traditionally formed by a mixture of smoke and fog in the atmosphere.
2. Asthma and bronchitis are two common respiratory diseases caused by breathing polluted air.

Teacher's Note:
a) Smog severely reduces atmospheric visibility.
b) Particulate matter and toxic gases lodge deep inside human lungs.

 

6. Give reasons of the following : (i) We are lucky that ozone is not stable near the earth's surface. (ii) The combustion of fossil fuels increases the amount of suspended particles in air. [2 Marks]

Answer:
1. (i) Ozone is a deadly poisonous gas if inhaled directly at ground level.
2. (ii) Fossil fuels are carbon-based and their incomplete combustion releases unburnt carbon particles and soot into the air.

Teacher's Note:
a) Stratospheric ozone protects us, but tropospheric ozone is a pollutant.
b) Suspended particles lower air quality and cause visibility issues.

 

7. Why is water so necessary for all living organisms ? Mention any two points in support of your answer. 'Water is known as A Wonder Liquid'. Justify this statement by giving any two reasons. [4 Marks]

Answer:
1. Cellular processes take place in water medium as all cellular reactions occur between substances dissolved in water.
2. Transportation of substances inside the body happens in a dissolved form, requiring a steady water medium.
3. Water has a high specific heat capacity, helping organisms maintain internal body temperature.
4. Terrestrial life requires freshwater to get rid of waste products and maintain osmotic balance.

Teacher's Note:
a) Protoplasm consists largely of water, making it the physical basis of life.
b) It acts as a universal solvent for biochemical reactions.
c) Water covers three-fourths of the Earth's surface.
d) Mentioning both physiological necessity and chemical uniqueness ensures full marks.

 

8. What is atmospheric fixation of Nitrogen ? [1 Mark]

Answer:
1. The high temperatures created during lightning flashes convert atmospheric nitrogen and oxygen into nitrogen oxides, which dissolve in rain to form nitrates and nitrites.

Teacher's Note:
a) Lightning provides the high energy needed to break strong nitrogen triple bonds.

 

9. What is soil erosion ? State any one way by which it can be prevented. [2 Marks]

Answer:
1. Soil erosion is the displacement of the upper layer of soil by wind or water action.
2. It can be prevented by extensive tree plantation or afforestation.

Teacher's Note:
a) Plant roots anchor soil particles securely.
b) Reducing overgrazing is another effective prevention strategy.

 

10. What is humus ? What is the role of earth worms in increasing the quantity of humus ? [2 Marks]

Answer:
1. Humus is the dark, organic material in soil made up of decaying plant and animal matter.
2. Earthworms consume organic debris and excrete nutrient-rich castings, thereby increasing humus content and aerating the soil.

Teacher's Note:
a) Humus gives soil its dark texture and water-retention capacity.
b) Earthworms are termed farmer's friends due to this contribution.

 

11. List two ways by which carbon dioxide is 'fixed' in the environment. [2 Marks]

Answer:
1. Green plants convert carbon dioxide into glucose during photosynthesis in the presence of sunlight.
2. Many marine animals use carbonates dissolved in sea water to make their shells.

Teacher's Note:
a) Photosynthesis is the primary carbon fixation mechanism on land.
b) Marine sedimentation locks carbon in geological formations over long periods.

 

12. Name two diseases caused due to an increased content of pollutants in the air produced due to the burning of fossil fuels. [2011 (T-II)] [1 Mark]

Answer:
1. Asthma and allergies (or lung cancer and bronchitis).

Teacher's Note:
a) Air pollutants irritate delicate respiratory tissues.

 

13. The heaps of solid waste are a menace. Give two reasons. [2 Marks]

Answer:
1. They act as breeding grounds for disease-causing vectors like mosquitoes, rats, and flies.
2. Toxic substances from waste can leach into the soil and contaminate groundwater resources.

Teacher's Note:
a) Improper solid waste management leads to foul odours and air pollution.
b) Non-biodegradable plastics persist in landfills for centuries.

 

14. How addition of undesirable substances and change in temperature affect the water life. [3 Marks]

Answer:
1. Toxic substances like heavy metals or pesticidespoison aquatic flora and fauna.
2. Addition of fertilisers causes eutrophication, reducing dissolved oxygen levels.
3. Sudden temperature changes disrupt breeding habits and kill sensitive aquatic organisms due to thermal shock.

Teacher's Note:
a) Aquatic organisms are sensitive to chemical composition changes.
b) Higher water temperatures decrease dissolved oxygen solubility.
c) Industrial waste is a major contributor to thermal pollution.

 

15. State any two harmful effects each of : (a) Air pollution and (b) Water pollution [2 Marks]

Answer:
1. (a) Air pollution causes respiratory diseases and global warming.
2. (b) Water pollution spreads water-borne diseases like cholera and harms aquatic life.

Teacher's Note:
a) Both forms of pollution degrade environmental quality globally.
b) Preventive measures are crucial for sustainable ecosystems.

 

16. What is the role of atmosphere in climate control ? [3 Marks]

Answer:
1. The atmosphere acts as a protective blanket covering the Earth.
2. It prevents sudden increases in temperature during daylight hours.
3. It slows down the escape of heat into outer space during night, maintaining a steady average global temperature.

Teacher's Note:
a) Air is a poor conductor of heat.
b) Atmospheric circulation redistributes heat across the globe.
c) Without an atmosphere, Earth's temperature would fluctuate wildly.

 

17. What percentage of nitrogen and oxygen is present in air ? [1 Mark]

Answer:
1. Nitrogen is 78 percent and oxygen is 21 percent by volume in air.

Teacher's Note:
a) These two gases constitute nearly 99 percent of the atmosphere.

 

18. Mention any two human activities which are responsible for water pollution. [2 Marks]

Answer:
1. Dumping untreated industrial effluents directly into rivers and lakes.
2. Discharging domestic sewage and washing activities in water bodies.

Teacher's Note:
a) Industrial waste contains toxic chemicals.
b) Sewage adds harmful pathogens and organic waste.

 

19. Mention the role of ozone layer in the atmosphere. [2 Marks]

Answer:
1. The ozone layer absorbs harmful ultraviolet radiation coming from the sun.
2. It protects living organisms on Earth from dangerous mutations, skin cancers, and eye damage.

Teacher's Note:
a) It is located in the stratosphere.
b) Ozone depletion poses severe environmental threats.

 

20. Give reason Lichens do not grow in Delhi whereas they commonly grow in Manali or Darjeeling. [2 Marks]

Answer:
1. Lichens are sensitive pollution indicators that fail to grow in sulphur dioxide-polluted environments.
2. Delhi has high air pollution levels from vehicular and industrial emissions, whereas hill stations like Manali or Darjeeling have cleaner air.

Teacher's Note:
a) Lichens serve as natural bioindicators of air quality.
b) Sulphur dioxide destroys lichen tissues rapidly.

 

21. What causes acid rain? Mantion any damage caused by it on living organisms. [2 Marks]

Answer:
1. It is caused by sulphur dioxide and nitrogen dioxide mixing with rainwater.
2. It makes water bodies acidic, killing aquatic life, and damages plant foliage.

Teacher's Note:
a) Fossil fuel emissions are the prime source.
b) It corrodes buildings and historical monuments.

 

22. What is Green House Effect ? Name compounds causing depletion of Ozone layer ? [2 Marks]

Answer:
1. The trapping of thermal radiation by atmospheric gases to keep Earth warm is called the greenhouse effect.
2. Chlorofluorocarbons (CFCs) are the primary compounds causing ozone layer depletion.

Teacher's Note:
a) Greenhouse gases regulate global temperatures.
b) CFCs release chlorine atoms that break down ozone molecules.

 

23. How do Sun and wind influence the formation of soil ? [3 Marks]

Answer:
1. The sun heats up rocks during the day, causing them to expand, and cools them at night, causing them to contract, leading to cracking and breaking.
2. Water entering these cracks freezes and expands, widening the cracks further.
3. Fast-blowing winds cause abrasive friction by carrying sand particles, wearing down rocks into smaller particles.

Teacher's Note:
a) This process is known as weathering of rocks.
b) It takes thousands of years to form a thin layer of soil.
c) Physical and chemical factors both play a role.

 

24. List any two consequences of global warming. [2 Marks]

Answer:
1. Melting of polar ice caps and glaciers, leading to a rise in sea levels.
2. Disruption of weather patterns causing frequent floods, droughts, and erratic rainfall.

Teacher's Note:
a) Global warming results from excess greenhouse gases.
b) Coastal cities face severe submersion threats.

 

25. Mention any four measures that should be taken to maintain the soil fertility. [4 Marks]

Answer:
1. Practice crop rotation to restore natural nutrients in the soil.
2. Use organic manures and compost instead of excessive chemical fertilisers.
3. Prevent overgrazing by animals to avoid topsoil loss.
4. Plant trees and practise afforestation to bind soil particles together.

Teacher's Note:
a) Chemical fertilisers degrade soil structure over time.
b) Humus replenishment keeps soil biologically active.
c) Contour ploughing prevents soil washing on slopes.
d) Sustainable farming practices ensure long-term agricultural productivity.

 

26. Give the chemical formula of ozone. What is its role in atmosphere ? [2 Marks]

Answer:
1. The chemical formula of ozone is \(\text{O}_3\).
2. It absorbs harmful ultraviolet rays from sunlight, preventing them from reaching the Earth's surface.

Teacher's Note:
a) It is an allotrope of oxygen.
b) Protection from UV rays prevents skin cancers in humans.

 

27. How the presence of pollutants present in the air does affect our health ? [2 Marks]

Answer:
1. Breathing polluted air causes diseases of the respiratory and circulatory systems.
2. It increases the incidence of allergies, asthma, bronchitis, and lung cancer.

Teacher's Note:
a) Air pollutants like carbon monoxide and sulfur dioxide damage internal organs.
b) Children and elderly people are most vulnerable to airborne toxins.

 

28. Name two air pollutants which when dissolve with water gives rise to acid rain. [1 Mark]

Answer:
1. Oxides of sulfur (such as sulfur dioxide, SO₂).
2. Oxides of nitrogen (such as nitrogen dioxide, NO₂).

Teacher's Note:
a) These gases dissolve in rainwater to form sulfuric and nitric acids.

 

29. Name two measures that can be taken to reduce water pollution. [2 Marks]

Answer:
1. Treating industrial effluents and sewage before discharging them into water bodies.
2. Minimizing the use of synthetic fertilizers and chemical pesticides in agriculture.

Teacher's Note:
a) Proper waste management protects aquatic life from toxic poisoning.
b) Avoid dumping household garbage directly into rivers or ponds.

 

30. Suggest two methods to control air pollution. [2 Marks]

Answer:
1. Using clean and eco-friendly fuels like CNG and solar energy.
2. Fitting industrial chimneys with filters and electrostatic precipitators to trap harmful soot particles.

Teacher's Note:
a) Public transport usage also significantly reduces vehicular emissions.
b) Strict enforcement of emission standards helps lower urban smog levels.

 

31. Differentiate between biodegradable and nonbiodegradable pollutants. [3 Marks]

Answer:
1. Biodegradable pollutants are easily broken down into harmless substances by natural biological processes.
2. Non-biodegradable pollutants cannot be broken down by biological agents and remain in the environment for a long time.
3. Examples of biodegradable waste include vegetable peels, whereas non-biodegradable waste includes plastics and synthetic pesticides.

Teacher's Note:
a) Biodegradable matter recycles easily through natural decomposition cycles.
b) Non-biodegradable substances cause biological magnification in food chains.
c) Proper segregation at source is essential for waste management.

 

32. Name the process that returns oxygen to the atmosphere. [1 Mark]

Answer:
1. Photosynthesis.

Teacher's Note:
a) Green plants release oxygen as a byproduct during food preparation.

 

33. Write the condition responsible for poor visibility in cold weather. [1 Mark]

Answer:
1. The presence of suspended pollutant particles like unburnt carbon and dust acting as condensation nuclei for water vapor, forming smog.

Teacher's Note:
a) Smog severely reduces visibility and causes severe respiratory irritation.

 

34. Which symbiotic life forms can grow on stones and help in the formation of soil ? Write the mode of their action for making soil from rocks. [3 Marks]

Answer:
1. Lichens are the symbiotic life forms that grow on bare rocks.
2. They release certain substances or acids that corrode and powder the rock surface.
3. This process breaks down the rocky surface into fine particles, creating a thin layer of soil.

Teacher's Note:
a) Lichens represent a mutualistic association between algae and fungi.
b) They are known as pioneer colonisers in ecological succession on rocks.
c) Chemical weathering by organic acids is the core mechanism here.

 

35. Why does moon have very cold and very hot temperature variations i.e. from -190°C to 110°C even though it is at the same distance from the sun as earth ? [3 Marks]

Answer:
1. The moon does not have an atmosphere surrounding it like the earth does.
2. An atmosphere acts as a blanket that prevents sudden fluctuations in temperature during day and night.
3. Without this insulating blanket, the moon's surface experiences extreme heat when exposed to sunlight and extreme cold when deprived of it.

Teacher's Note:
a) The absence of air prevents heat retention or distribution across hemispheres.
b) Earth's atmosphere traps outgoing terrestrial radiation effectively.
c) Distance from the sun is not the sole factor determining planetary surface temperature.

 

36. Why does Mathura refinery pose problem to the Taj Mahal ? [2 Marks]

Answer:
1. The refinery releases sulfur dioxide and other pollutants into the atmosphere.
2. These gases cause acid rain, which reacts with the marble (calcium carbonate) of the Taj Mahal and corrodes it.

Teacher's Note:
a) This phenomenon is often referred to as marble cancer.
b) Industrial emissions near historical monuments require strict regulatory control.

 

37. Explain the role of atmosphere as a blanket. List the factors deciding the rainfall patterns. [4 Marks]

Answer:
1. The atmosphere keeps the average temperature of the earth steady during the day and even across the course of the year by preventing the sudden escape of heat into outer space.
2. Rainfall patterns are decided by the prevailing wind patterns and large scale atmospheric circulation.
3. The approach of water-laden winds from oceans also determines regional precipitation.
4. Geographical features like mountain ranges influence where rain clouds drop their moisture.

Teacher's Note:
a) Air acts as a poor conductor of heat, aiding its blanket effect.
b) Convection currents drive seasonal monsoon systems globally.
c) Condensation of water vapor is driven by temperature drops in upper air masses.
d) Topography plays a major role in local rain shadow effects.

 

38. State the effect of the following on aquatic organisms- (a) Removal of dissolved oxygen (b) Change in temperature [2 Marks]

Answer:
1. (a) Removal of dissolved oxygen causes suffocation and eventual death of aquatic animals like fish.
2. (b) A sudden change in water temperature disturbs breeding cycles and can kill sensitive aquatic organisms.

Teacher's Note:
a) Thermal pollution lowers oxygen solubility in aquatic bodies.
b) Biological oxygen demand rises when organic pollutants enter water systems.

 

39. How do forest play an important role in maintaining water cycle. [2 Marks]

Answer:
1. Forests help in transpiration, releasing large amounts of water vapor into the atmosphere to form clouds.
2. Tree roots promote groundwater recharge by facilitating the seepage of rainwater into the soil.

Teacher's Note:
a) Vegetation cover directly influences local humidity and precipitation rates.
b) Deforestation disrupts hydrological cycles and reduces freshwater availability.

 

40. Name the two gases given out by burning of fossil fuels which dissolve in rain water to form acid rain. [1 Mark]

Answer:
1. Sulfur dioxide and nitrogen dioxide.

Teacher's Note:
a) Combustion of coal and petroleum products releases these acidic precursor gases.

 

41. Why is atmosphere essontial for life? Write two points in support of your answer. [2 Marks]

Answer:
1. It provides essential gases like oxygen for respiration, carbon dioxide for photosynthesis, and nitrogen for plant growth.
2. It acts as a protective blanket that shields the earth from harmful ultraviolet radiation and maintains a stable temperature range.

Teacher's Note:
a) Ozone layer absorption occurs in the upper stratosphere.
b) Without gaseous exchange in the atmosphere, biological life could not survive.

 

42. List any four activities that you think would lead to air pollution. [2 Marks]

Answer:
1. Burning of fossil fuels in vehicles and thermal power plants.
2. Release of toxic industrial fumes and gases from factories.
3. Deforestation and large scale burning of agricultural waste.
4. Use of CFCs and construction activities creating heavy airborne dust.

Teacher's Note:
a) Vehicular exhaust is a major contributor in metropolitan areas.
b) Dust particles from construction clog respiratory tracts.

 

43. How are clouds formed ? [2 Marks]

Answer:
1. Water bodies heat up during the day, causing water to evaporate and rise into the atmosphere along with hot air.
2. As the air rises, it expands and cools, causing the water vapor to condense into tiny droplets around dust particles to form clouds.

Teacher's Note:
a) Condensation nuclei play a vital role in cloud droplet aggregation.
b) Adiabatic cooling drives upper-atmosphere cloud formation.

 

44. Why do terrestrial forms require fresh water ? [2 Marks]

Answer:
1. Terrestrial organisms cannot tolerate high salt concentrations found in marine water.
2. Fresh water is essential to maintain cellular osmotic balance and carry out vital metabolic reactions within their bodies.

Teacher's Note:
a) Body fluids of land animals require low solute concentrations.
b) Drinking saltwater leads to severe dehydration in terrestrial species.

 

45. Mention any two processes involved in water cycle. [2 Marks]

Answer:
1. Evaporation and transpiration.
2. Condensation and precipitation.

Teacher's Note:
a) Solar energy powers the continuous movement of water on earth.
b) Precipitation returns atmospheric moisture back to land and oceans.

 

46. How do fossil fuel cause air-pollution ? [2 Marks]

Answer:
1. Burning fossil fuels releases oxides of sulfur and nitrogen, along with carbon dioxide and unburnt carbon particles.
2. These emissions cause smog, acid rain, and global warming.

Teacher's Note:
a) Carbon monoxide poisoning occurs from incomplete fuel combustion.
b) Particulate matter increases respiratory disease rates significantly.

 

47. What is top soil ? Mention any two factors that decide which plants will thrive on that soil. [2 Marks]

Answer:
1. Top soil is the uppermost layer of soil containing humus, nutrient minerals, and living organisms.
2. The nutrient content of the soil and the amount of water it can retain decide which plants will thrive there.

Teacher's Note:
a) Humus provides essential fertility and water-holding capacity.
b) Soil texture and pH also dictate plant survival.

 

48. How do the rivers from land, add minerals to sea water? [2 Marks]

Answer:
1. As rivers flow over rocks and soil on land, they dissolve and wash away soluble minerals.
2. These dissolved minerals are carried along the river currents and eventually deposited into the sea.

Teacher's Note:
a) Continuous mineral accumulation contributes to ocean salinity.
b) Weathering of continental rocks is the primary mineral source.

 

49. How can we prevent the loss of top soil? [2 Marks]

Answer:
1. By increasing vegetation cover and planting trees (afforestation) to bind soil particles.
2. By practicing terrace farming and contour ploughing on slopes to prevent soil erosion by wind or running water.

Teacher's Note:
a) Overgrazing by cattle should be restricted to protect topsoil.
b) Windbreaks and shelterbelts reduce wind erosion in arid fields.

 

50. Why does the percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere? [3 Marks]

Answer:
1. Atmospheric gases are regulated through continuous biogeochemical cycles in nature.
2. For instance, oxygen is consumed in respiration and combustion, but replenished through photosynthesis.
3. Similarly, carbon dioxide is released via respiration and burning, but absorbed by plants and oceans, maintaining a steady balance.

Teacher's Note:
a) Dynamic equilibrium exists among atmospheric reservoirs.
b) Nitrogen fixation and denitrification balance atmospheric nitrogen levels.
c) Human activities can disrupt these natural balancing feedback loops.

 

51. Lichens are called pioneer colonisers of bare rock. How can they help in formation of soil? [2 Marks]

Answer:
1. Lichens grow on rocky surfaces and secrete mild acids that etch and powder the rock.
2. Over time, this chemical breakdown creates a thin layer of soil suitable for the growth of small plants like mosses.

Teacher's Note:
a) They initiate primary ecological succession on barren substrates.
b) Organic debris from dead lichens adds humus to the newly formed soil.

 

5. Why do people love to fly kites near the seashore? [2 Marks]

Answer:
1. Near the seashore, sea breezes blow steadily due to differential heating of land and water during the day.
2. These strong, consistent onshore winds provide ideal conditions for flying kites easily.

Teacher's Note:
a) Convection currents drive sea breeze circulation.
b) Air moves from high-pressure cool sea areas to low-pressure warm land areas.

 

52. Why does water need conservation even though large oceans surround the land masses? [3 Marks]

Answer:
1. The vast majority of water on earth is in oceans and is saline, making it unfit for drinking and agriculture.
2. The availability of fresh water is very limited and unevenly distributed across the globe.
3. Depleting groundwater tables and pollution of rivers make freshwater conservation vital for survival.

Teacher's Note:
a) Less than three percent of global water is fresh water.
b) Desalination processes are expensive and energy-intensive.
c) Proper watershed management ensures sustainable freshwater supplies.

 

53. "Soil is formed by water." If you agree to this statement then give reasons. [3 Marks]

Answer:
1. Fast-flowing rainwater and rivers wear down large rocks by crashing them against each other and washing away fragments.
2. Water enters cracks in rocks, freezes, expands, and splits rocks into smaller pieces.
3. Water acts as a primary agent of both physical and chemical weathering to create soil particles.

Teacher's Note:
a) Mechanical abrasion by running water grinds rocks into silt and sand.
b) Freeze-thaw cycles powered by water cause mechanical weathering.
c) Water also transports weathered materials to form sedimentary deposits.

 

54. During summer, if you go near the lake, you feel relief from the heat. Why? [2 Marks]

Answer:
1. Water has a high specific heat capacity and absorbs heat from the surroundings slowly.
2. Cool breezes blowing from the lake surface towards the land lower the ambient temperature, providing relief from summer heat.

Teacher's Note:
a) Evaporation of water from the lake surface also creates a cooling effect.
b) Local convection currents operate similarly to coastal sea breezes.

 

55. "The flow of energy is unidirectional whereas the biogeochemical transfer is cyclic". Explain why ? [3 Marks]

Answer:
1. Energy enters ecosystems from the sun, flows in one direction through trophic levels, and is eventually lost as heat, never returning to the sun.
2. In contrast, nutrients and chemical elements are repeatedly used and recycled between living organisms and the physical environment.
3. Thus, energy flow is a one-way path, while matter circulation operates in closed loops.

Teacher's Note:
a) The First and Second Laws of Thermodynamics govern unidirectional energy flow.
b) Biogeochemical cycles ensure nutrient conservation within the biosphere.
c) Matter is conserved, whereas usable energy degrades into heat at every trophic transfer.

 

56. Justify the statement "The nitrogen cycle is supposed to be an ideal cycle in the biosphere". [3 Marks]

Answer:
1. Nitrogen gas makes up about 78 percent of the atmosphere and acts as an endless reservoir.
2. Specialized microorganisms fix atmospheric nitrogen into usable nitrates and nitrites for plants.
3. Denitrifying bacteria eventually return nitrogen gas back to the atmosphere, maintaining a perfect balance.

Teacher's Note:
a) Biological fixation bridges inert atmospheric nitrogen with living tissues.
b) The cycle maintains constant atmospheric composition through continuous feedback.
c) Rhizobium bacteria in legume root nodules play a central role here.

 

57. List three ways to control soil pollution. [3 Marks]

Answer:
1. Reducing the usage of chemical fertilizers and synthetic pesticides by adopting organic farming.
2. Properly treating industrial and municipal waste before disposing of it on land.
3. Practicing recycling of non-biodegradable materials like plastics and planting trees to prevent erosion.

Teacher's Note:
a) Landfills should be managed safely to prevent soil leaching.
b) Bioremediation uses microbes to clean up contaminated soils.
c) Tree plantation stabilizes loose topsoil against heavy runoff.

58. In coastal area, wind current moves from the sea towards the land during day; but during night it moves from land to the sea. Discuss the reason. [3 Marks]

Answer:
1. During the day, the land gets heated faster than the sea, causing the air above the land to rise and create a low-pressure area.
2. Cool air from the sea moves towards the land to take its place, forming the sea breeze.
3. During the night, the land cools down faster than the sea, making the air above the sea warmer and lighter, which causes wind to blow from the land to the sea as a land breeze.

Teacher's Note:
a) This phenomenon is caused by differential heating and cooling of land and water.
b) Students often confuse the directions of sea breeze and land breeze.
c) Convection currents in the atmosphere drive this coastal wind cycle.

 

59. Following are a few organisms (a) lichen (b) mosses (c) mango tree (d) actus. Which among the above can grow on stones; and also help in formation of soil? Write the mode of their action for making soil. [3 Marks]

Answer:
1. Lichen and mosses can grow on bare stones and help in soil formation.
2. Lichens release certain substances that powder the rock surface and cause weathering to form a thin layer of soil.
3. Mosses grow on this thin layer and cause further breaking down of the rocks into fine soil particles.

Teacher's Note:
a) Lichens act as pioneer species in primary succession on rocks.
b) Note that 'actus' is a typographical error in the question for cactus.
c) Biological weathering plays a crucial role in soil formation alongside physical and chemical factors.

 

60. Why does moon have very cold and very hot temperature variations, eg. from -190°C to 110°C even though it is at the same distance from the Sun as the Earth is? [3 Marks]

Answer:
1. The moon does not have an atmosphere surrounding it like the Earth does.
2. An atmosphere acts as a blanket that absorbs and traps heat, preventing extreme temperature fluctuations.
3. Without an atmosphere, the moon experiences uninhibited heating during the day and rapid loss of heat into space during the night.

Teacher's Note:
a) Distance from the Sun is not the sole determinant of surface temperature.
b) Atmospheric insulation is key to maintaining a moderate climate on Earth.
c) The absence of greenhouse gases on the moon causes extreme diurnal temperature ranges.

 

61. There is mass mortality of fishes in a pond. What may be the reasons? [3 Marks]

Answer:
1. Depletion of dissolved oxygen in the water due to excessive organic pollution or eutrophication.
2. Sudden toxic chemical contamination or industrial effluent discharge into the pond.
3. Extreme fluctuations in water temperature or pH levels beyond the survival range of fishes.

Teacher's Note:
a) Eutrophication leads to algal blooms which deplete oxygen at night.
b) Thermal pollution can drastically reduce oxygen solubility in water.
c) Water quality parameters must be maintained for aquatic life survival.

 

62. Soil formation is done by both abiotic and biotic factors. List the names of these factors by classifying them as abiotic and biotic? [3 Marks]

Answer:
1. Abiotic factors include the sun, water, wind, and rock type.
2. Biotic factors include lichens, mosses, and other plants like roots of big trees.
3. Soil formation is a slow cumulative process resulting from the interaction of these factors.

Teacher's Note:
a) Abiotic factors cause mechanical and chemical weathering of rocks.
b) Biotic factors contribute through organic acids and physical penetration.
c) Clear classification helps distinguish physical from biological weathering agents.

 

63. All the living organisms are basically made up of C, N, S, P, H and O. How do they enter the living forms? Discuss. [3 Marks]

Answer:
1. Carbon, hydrogen, and oxygen enter living forms mainly through photosynthesis and respiration processes.
2. Nitrogen and sulfur are absorbed by plants from the soil in the form of inorganic salts and nitrates.
3. Phosphorus is taken up from soil minerals by plant roots and transferred through various trophic levels in food webs.

Teacher's Note:
a) Biogeochemical cycles govern the flow of these elements through ecosystems.
b) Producers convert inorganic nutrients into complex organic molecules.
c) Consumers obtain these essential elements by feeding on plants and other animals.

 

64. Why does the percentage of gases like oxygen, nitrogen and carbon dioxide remain almost the same in the atmosphere? [3 Marks]

Answer:
1. Atmospheric gases are regulated through continuous biogeochemical cycles that balance consumption and release.
2. Photosynthesis balances oxygen release with carbon dioxide absorption, while respiration does the reverse.
3. Nitrogen is fixed and returned to the atmosphere continuously through the nitrogen cycle, maintaining equilibrium.

Teacher's Note:
a) Dynamic equilibrium maintains atmospheric composition over geological time scales.
b) Human interference can disrupt these delicate natural balances.
c) Sinks and sources act in harmony to stabilize gas percentages.

 

65. Why are root nodules useful for the plants? [2 Marks]

Answer:
1. Root nodules contain symbiotic nitrogen-fixing bacteria such as Rhizobium.
2. These bacteria convert atmospheric nitrogen into usable nitrogen compounds for the plant.

Teacher's Note:
a) Leguminous plants depend heavily on this mutualistic association.
b) This naturally enriches soil fertility without requiring artificial nitrogen fertilizers.

 

66. Many human activities lead to increasing levels of pollutions of air, water bodies and soil. "Isolating these activities to specific and limited areas would not help in reducing pollution". Justify this statement giving at least five reasons. [5 Marks]

Answer:
1. Pollutants like air and water contaminants are mobile and easily transported across regional boundaries by wind and water currents.
2. Global phenomena like acid rain and global warming affect areas far removed from the original pollution source.
3. Water bodies flow continuously, carrying dissolved pollutants downstream across different states and countries.
4. Soil pollutants can leach into groundwater tables, contaminating large underground aquifers spread over vast regions.
5. Ecosystems are interconnected globally, meaning localized control cannot prevent widespread ecological degradation.

Teacher's Note:
a) Pollution respects no political or geographic boundaries.
b) Comprehensive global and regional environmental policies are essential.
c) Air and water are fluid media that actively disperse pollutants.
d) Sustainable practices at the source are required rather than mere isolation.

 

67. Explain with the help of a labelled diagram carbon cycle in nature. [3 Marks]

Answer:

[Figure: Diagram of carbon cycle showing carbon dioxide in atmosphere, photosynthesis by plants, respiration by animals, combustion of fossil fuels, and decomposition by microorganisms]

1. Carbon dioxide from the atmosphere is taken up by plants during photosynthesis to form organic compounds.
2. These carbon compounds pass through food chains from plants to herbivores and carnivores.
3. Carbon is returned to the atmosphere through respiration, decomposition of dead organic matter, and combustion of fossil fuels.

Teacher's Note:
a) Carbon is the foundational building block of all organic life on Earth.
b) Fossil fuel burning has accelerated carbon input, causing climate imbalance.
c) Balanced sinks like oceans and forests help absorb excess atmospheric carbon.

 

68. Describe green house effect. How the presence of green house gases would lead to global warming ? Explain. [3 Marks]

Answer:
1. Greenhouse gases trap heat radiated from the Earth's surface, keeping the planet warm enough to sustain life.
2. An increase in the concentration of greenhouse gases like carbon dioxide and methane traps more heat than normal.
3. This excess heat retention leads to a progressive increase in average global temperatures, known as global warming.

Teacher's Note:
a) The natural greenhouse effect is vital, but its enhancement is dangerous.
b) Human activities like deforestation and fossil fuel combustion drive global warming.
c) Consequences include melting ice caps and rising sea levels.

 

69. Draw a neat labelled diagram of water cycle in nature. [3 Marks]

Answer:

[Figure: Diagram of water cycle showing evaporation from oceans, transpiration from plants, condensation forming clouds, precipitation, and collection in water bodies]

1. Water evaporates from water bodies and transpires from plants into the atmosphere.
2. Water vapor cools and condenses to form clouds in the upper atmosphere.
3. Precipitation falls back to Earth as rain or snow, replenishing water bodies and completing the cycle.

Teacher's Note:
a) Solar energy drives the continuous evaporation of water.
b) The water cycle maintains freshwater availability across the globe.
c) Transpiration from vegetation contributes significantly to atmospheric moisture.

 

70. With the help of a neat labelled diagram, depict the cycling of carbon in nature. [3 Marks]

Answer:

[Figure: Diagram showing carbon cycle with atmospheric CO2, photosynthesis, plant and animal respiration, fossil fuels, and decomposition]

1. Atmospheric carbon dioxide is fixed by green plants during photosynthesis.
2. Carbon is transferred to animals via feeding and released back via respiration.
3. Decomposition of dead matter and burning of fossil fuels return carbon dioxide to the atmosphere.

Teacher's Note:
a) Carbon cycles rapidly between biotic and abiotic components.
b) Oceans act as massive carbon reservoirs.
c) Diagrams must clearly show arrows indicating the direction of carbon flow.

 

71. Mention the two ways in which carbon dioxide is fixed in the environment. [2 Marks]

Answer:
1. Plants convert carbon dioxide into glucose using sunlight during photosynthesis.
2. Marine animals use dissolved carbonates to build their calcium carbonate shells.

Teacher's Note:
a) Photosynthesis is the primary terrestrial carbon fixation mechanism.
b) Marine fixation helps regulate oceanic carbon concentration.

 

72. Make neat and labelled sketch of Nitrogen cycle in nature. [3 Marks]

Answer:

[Figure: Diagram of nitrogen cycle showing atmospheric nitrogen, nitrogen fixation by bacteria and lightning, uptake by plants, animal consumption, nitrification, and denitrification]

1. Atmospheric nitrogen is fixed by bacteria and lightning into nitrates and nitrites in soil.
2. Plants absorb these nitrogen compounds to synthesize proteins, which pass to animals through food chains.
3. Decomposers convert organic nitrogen back into ammonia, and denitrifying bacteria return nitrogen gas to the atmosphere.

Teacher's Note:
a) Nitrogen makes up 78 percent of air but cannot be used directly by most organisms.
b) Microorganisms play an indispensable role in every step of the nitrogen cycle.
c) Lightning provides high energy to fix atmospheric nitrogen directly.

 

73. Describe in brief the role of Nitrogen fixing bacteria and of lightening in fixing atmospheric nitrogen. [3 Marks]

Answer:
1. Nitrogen-fixing bacteria (like Rhizobium in legume root nodules or free-living soil bacteria) convert atmospheric nitrogen gas into ammonia.
2. Lightning provides high temperature and pressure energy that combines atmospheric nitrogen and oxygen to form nitrogen oxides.
3. These nitrogen oxides dissolve in rain to form dilute nitric acid, which adds nitrates to the soil for plant use.

Teacher's Note:
a) Both biological and physical methods are essential for nitrogen fixation.
b) Ammonia is further converted into nitrates by nitrifying bacteria.
c) This process makes inert atmospheric nitrogen accessible to living organisms.

 

74. In coastal area, wind current moves from sea towards the land during day; but during night it moves from land to sea. Discuss the reason. [3 Marks]

Answer:
1. During the day, land heats up faster than the sea, causing warm air over land to rise and create low pressure.
2. Cooler air from the sea rushes towards the land, resulting in a sea breeze.
3. During the night, land cools faster than the sea, making air over the sea warmer and causing wind to blow from land to sea as a land breeze.

Teacher's Note:
a) Water has a higher specific heat capacity than land.
b) This creates diurnal pressure differences driving local winds.
c) Repeated question from item 58, testing coastal wind dynamics.

 

75. How are CFCs harmful for the environment and living beings ? [3 Marks]

Answer:
1. Chlorofluorocarbons (CFCs) release chlorine atoms in the stratosphere when broken down by UV radiation.
2. These chlorine atoms catalyze the destruction of the ozone layer, reducing its thickness.
3. Ozone depletion allows harmful ultraviolet rays to reach Earth's surface, causing skin cancer, cataracts, and damage to crops.

Teacher's Note:
a) CFCs were widely used in refrigerators and aerosols before being phased out.
b) A single chlorine atom can destroy thousands of ozone molecules.
c) International treaties like the Montreal Protocol regulate CFC emissions.

 

76. What are the forms of oxygen found in the atmosphere ? [2 Marks]

Answer:
1. Elemental diatomic oxygen (O₂), which is essential for respiration.
2. Ozone (O₃), which is a triatomic molecule found in the stratosphere.

Teacher's Note:
a) Diatomic oxygen makes up about 21 percent of the atmosphere.
b) Ozone is present in trace amounts but plays a protective role.

 

77. "Forests influence the quality of our air, soil and water resources". Justify the statement. [4 Marks]

Answer:
1. Forests purify air by absorbing carbon dioxide and releasing oxygen through photosynthesis.
2. Tree roots bind soil particles firmly, preventing soil erosion and maintaining soil fertility.
3. Forests enhance groundwater recharge by facilitating rainwater infiltration into the soil.
4. They regulate regional humidity and local water cycles through plant transpiration.

Teacher's Note:
a) Forests act as vital lungs and sponges of the Earth's ecosystems.
b) Deforestation severely impacts all three major environmental resources.
c) Biodiversity thrives best in dense, protected forest cover.
d) Watershed protection prevents downstream flooding and siltation.

 

78. Mention the two forms of oxygen found in atmosphere. [2 Marks]

Answer:
1. Free diatomic oxygen (O₂).
2. Ozone (O₃).

Teacher's Note:
a) This is a direct recall question on atmospheric oxygen allotropes.
b) O₂ supports aerobic life while O₃ shields against UV radiation.

 

79. Name the form of oxygen absorbing U.V. rays. [1 Mark]

Answer:
Ozone (O₃).

Teacher's Note:
a) Ozone absorbs harmful ultraviolet radiation from the Sun in the stratosphere.

 

80. Draw flow diagram of oxygen cycle. [3 Marks]

Answer:
1. Atmospheric Oxygen (O₂) is utilized by organisms for Respiration.
2. Respiration and combustion release Carbon Dioxide and Water into the environment.
3. Green plants take up Carbon Dioxide and Water to perform Photosynthesis, releasing Oxygen back into the atmosphere.

Teacher's Note:
a) The oxygen cycle maintains a steady level of oxygen in the air.
b) Photosynthesis is the primary source of atmospheric oxygen replenishment.
c) Aerobic respiration consumes most of the free oxygen.

 

81. What do you understand by ozone layer depletion ? [2 Marks]

Answer:
1. Ozone layer depletion is the thinning of the ozone layer in the stratosphere.
2. It is caused by pollutants such as chlorofluorocarbons (CFCs) reacting with and destroying ozone molecules.

Teacher's Note:
a) Depletion allows dangerous UV radiation to penetrate to the Earth's surface.
b) Global cooperation has successfully curbed ozone-depleting substances.

 

82. What is air pollution ? How does air pollution affect animal and plant life ? [3 Marks]

Answer:
1. Air pollution is the contamination of air by harmful gases, dust, and smoke that alter its normal composition.
2. In animals and humans, it causes respiratory diseases, asthma, and cardiovascular disorders.
3. In plants, it damages leaves, reduces photosynthetic activity, and stunts overall growth.

Teacher's Note:
a) Major air pollutants include sulfur dioxide, nitrogen oxides, and particulate matter.
b) Acid rain resulting from air pollution damages forests and aquatic life.
c) Chronic exposure to polluted air severely reduces life expectancy.

 

83. Draw a labelled diagram to show carbon cycle in nature. [3 Marks]

Answer:

[Figure: Diagram showing carbon cycle with atmospheric CO2, plant photosynthesis, animal consumption, respiration, decomposition, and fossil fuel combustion]

1. Carbon dioxide from the atmosphere is absorbed by plants for photosynthesis.
2. Herbivores consume plants, and carnivores consume herbivores, passing carbon through the food web.
3. Respiration, decomposition, and combustion return carbon dioxide to the atmosphere.

Teacher's Note:
a) Carbon cycles continuously between living organisms and the environment.
b) Proper labeling of all arrows and reservoirs is essential for full credit.
c) This is a recurring concept tested across different question numbers in the paper.

 

84. What are the two ways by which CO2 is returned to the atmosphere ? [2 Marks]

Answer:
1. Respiration: Living organisms respire, releasing carbon dioxide as a byproduct into the atmosphere.
2. Combustion: Burning of fossil fuels, wood, and organic matter releases carbon dioxide.

Teacher's Note:
a) Carbon dioxide is a greenhouse gas vital for maintaining Earth's temperature.
b) Human activities have accelerated combustion processes beyond natural absorption capacities.

 

85. What are the causes of increase in the concentration of carbon dioxide in the atmosphere? How is carbon dioxide converted into organic compounds? Justify with the help of a labelled diagram. [3 Marks]

Answer:
1. Causes include massive burning of fossil fuels, deforestation, and industrial emissions.
2. Green plants convert carbon dioxide into glucose (organic compounds) during photosynthesis in the presence of sunlight and chlorophyll.
3. [Figure: Schematic diagram of carbon cycle showing plants taking in CO2 for photosynthesis and producing organic compounds]

Teacher's Note:
a) Photosynthesis bridges inorganic carbon and organic food webs.
b) Deforestation reduces the number of carbon sinks.
c) Excess carbon dioxide intensifies global warming.

 

86. Why is circulation of water necessary in the environment ? Discuss any two human activities which are disturbing the water cycle. [3 Marks]

Answer:
1. Water circulation ensures the continuous availability of fresh water for terrestrial life, agriculture, and climate regulation.
2. Deforestation reduces transpiration and disrupts local precipitation patterns.
3. Over-extraction of groundwater lowers the water table and reduces surface runoff balance.

Teacher's Note:
a) Water is the universal solvent and medium for all cellular metabolic reactions.
b) Human interference leads to severe droughts or erratic floods.
c) Sustainable water management is critical for biosphere survival.

 

87. With the help of a labelled diagram show the cycling of carbon in nature. What are the two ways in which carbon di-oxide is fixed in the environment. [3 Marks]

Answer:
1. [Figure: Labelled diagram of carbon cycle showing atmospheric CO2, photosynthesis in plants, respiration, combustion, and decomposition]
2. First way: Green plants fix carbon dioxide into glucose through photosynthesis.
3. Second way: Marine animals use carbonate dissolved in sea water to form their shells.

Teacher's Note:
a) Carbon is the backbone of all organic molecules in living systems.
b) Oceans act as massive carbon sinks absorbing atmospheric carbon dioxide.
c) Balance between fixation and release maintains steady atmospheric levels.

 

88. With the help of diagram depict the oxygen cycle in nature. What is the % of oxygen present in atmosphere ? What is the role of ozone layer and how is it getting depleted ? [4 Marks]

Answer:
1. [Figure: Diagram showing oxygen cycle with atmospheric oxygen, respiration, photosynthesis, and combustion processes]
2. The percentage of oxygen present in the atmosphere is approximately 21 percent.
3. The ozone layer absorbs harmful ultraviolet radiations coming from the sun, protecting life from mutations.
4. Ozone depletion is primarily caused by the release of chlorofluorocarbons (CFCs) used in refrigerators and aerosols.

Teacher's Note:
a) Oxygen is essential for aerobic respiration in most living organisms.
b) Ozone is an allotrope of oxygen with formula O₃.
c) UV radiation breaks down CFC molecules releasing free chlorine atoms.
d) Chlorine atoms catalytically destroy ozone molecules in the stratosphere.

 

89. How do clouds formed in the sky ? Draw the biogeochemical cycle involved in it. What are the different states in which water is found in the water cycle ? [3 Marks]

Answer:
1. Water evaporates from water bodies, rises, cools, and condenses on dust particles to form clouds.
2. [Figure: Flowchart of the water cycle showing evaporation, condensation, precipitation, and collection]
3. Water is found in three states: solid (snow, ice), liquid (water), and gas (water vapour).

Teacher's Note:
a) Condensation is an exothermic phase change driven by atmospheric cooling.
b) The water cycle is driven entirely by solar energy.
c) Water moves continuously between land, oceans, and the atmosphere.

 

90. What are biogeochemical cycles ? Draw a labelled diagram to illustrate cycling of oxygen in nature. Write the means of returning oxygen to the atmosphere. [3 Marks]

Answer:
1. Biogeochemical cycles are pathways through which chemical elements move through biotic and abiotic compartments of Earth.
2. [Figure: Labelled diagram of oxygen cycle showing cycling of oxygen between atmosphere, organisms, and water]
3. Oxygen is returned to the atmosphere primarily through photosynthesis carried out by green plants and algae.

Teacher's Note:
a) "Bio" refers to living organisms and "geo" to rocks, water, and air.
b) Nutrients are conserved and recycled endlessly within the biosphere.
c) Photosynthesis is the sole major biological source of atmospheric oxygen.

 

91. What is nitrogen fixation ? Why do plant need to fix nitrogen ? Draw a labelled diagram to illustrate nitrogen - cycle. [3 Marks]

Answer:
1. Nitrogen fixation is the conversion of inert atmospheric nitrogen gas into usable nitrogen compounds like nitrates and nitrites.
2. Plants need fixed nitrogen to synthesize essential biomolecules such as proteins, nucleic acids, and amino acids.
3. [Figure: Labelled diagram of nitrogen cycle showing fixation, nitrification, assimilation, ammonification, and denitrification]

Teacher's Note:
a) Atmospheric nitrogen cannot be utilized directly by most living organisms.
b) Rhizobium bacteria in legume root nodules perform biological nitrogen fixation.
c) Lightning also fixes atmospheric nitrogen into soil nitrates naturally.

 

92. Draw a labelled diagram of carbon cycle in nature. Describe the role of photosynthesis and respiration in carbon cycle. [3 Marks]

Answer:
1. [Figure: Labelled diagram of carbon cycle showing exchange of carbon between atmosphere, biosphere, and geosphere]
2. Photosynthesis removes carbon dioxide from the atmosphere and converts it into organic food compounds.
3. Respiration releases carbon dioxide back into the atmosphere by breaking down organic compounds to yield energy.

Teacher's Note:
a) Both processes maintain dynamic equilibrium of carbon in the atmosphere.
b) Photosynthesis is an anabolic process requiring solar energy.
c) Respiration is a catabolic process common to plants and animals.

 

93. Study the given figure of Nitrogen cycle and mention what do A, B, C, D, E represents. What will happen if step A does not occur? Write the role of N2 fixing bacteria in the [3 Marks]

Answer:
1. A: Nitrogen fixation, B: Uptake by plants (Assimilation), C: Ammonification, D: Nitrification, E: Denitrification.
2. If step A (nitrogen fixation) does not occur, plants will fail to get usable nitrogen compounds, halting protein synthesis and stunting growth.
3. Nitrogen-fixing bacteria convert inert atmospheric nitrogen gas into ammonia, which is further converted into nitrates usable by plants.

Teacher's Note:
a) Nitrogen cycle relies heavily on specialized soil microorganisms.
b) Leguminous plants share a symbiotic relationship with nitrogen-fixing bacteria.
c) Denitrifying bacteria complete the cycle by returning nitrogen gas to the atmosphere.

 

94. Biosphere. Name two biologically important compounds that contains both O2 and N2 [1 Mark]

Answer:
1. Proteins and Nucleic acids (DNA and RNA).

Teacher's Note:
a) Both compounds are fundamental building blocks of all living cells.

 

95. What are the types of natural resources? [2 Marks]

Answer:
1. Renewable resources: Resources that can be replenished relatively quickly by natural processes (e.g., solar energy, wind, water).
2. Non-renewable resources: Resources that are limited in abundance and take millions of years to form (e.g., coal, petroleum, natural gas).

Teacher's Note:
a) Conservation of non-renewable resources is crucial for future generations.
b) Natural resources form the life support system of the biosphere.

 

96. Why plants do not utilise nitrogen directly from atmosphere? [2 Marks]

Answer:
1. Atmospheric nitrogen exists as diatomic gas molecules (N₂) bound by a very strong triple covalent bond.
2. Plants lack the specialized enzymes required to break this strong triple bond and convert it into a usable form.

Teacher's Note:
a) Breaking the N₂ bond requires high energy inputs like lightning or nitrogenase enzymes.
b) Plants must absorb nitrogen in fixed forms like nitrates, nitrites, or ammonium ions.

ral Resources Sure Shot Questions C.