CBSE NCERT Notes for Class 9 Science Chapter 14 Natural Resources

RESOURCES ON THE EARTH AND THEIR IMPORTANCE

Natural resources are the components of nature that are not alive (abiotic). They are utilised by humans to satisfy their fundamental needs. The Earth’s natural resources are air, water, and land.

AIR : THE BREATH OF LIFE

The air we breathe is a combination of many gases, including nitrogen (N 2), oxygen (02), carbon dioxide (CO 2), and water vapours. The precise mix of these gases is what enables life on Earth to exist.

All cells, eukaryotic or prokaryotic, need oxygen to break down glucose molecules and get energy for their varied functions (by the process of respiration). This phenomenon results in the emission of carbon dioxide into the environment. 

The atmosphere is the gaseous envelope that surrounds the Earth. It serves a variety of critical functions, including protection from UV radiation and aiding in communication.

Other sources of co2 in the air include the following:

  1. combustion of fuels by humans
  2. forest fires

While these sources provide a huge portion of co2 to the atmosphere, the amount of carbon dioxide in the air is only a fraction of a percent. 

This is because co2 is fixed in two distinct ways.

  1. Photosynthesis is the process by which green plants convert carbon dioxide to glucose in the presence of sunshine.
  2.  Many marine animals create their shells from carbonates (dissolved in seawater).

There is no evidence of life on planets such as Venus or Mars. Carbon dioxide is the primary component of these planets’ atmospheres (it makes up 95-97 percent of the atmosphere). 

The following sections explore the fundamental relevance of the atmosphere.

Role Of Atmosphere In Climate Control : The atmosphere acts as a protective blanket over the Earth. Air is an inefficient conductor of heat. Thus, the atmosphere prevents the temperature from suddenly rising during the daytime hours. Similarly, at night, it reduces the rate at which heat escapes into outer space.

Thus, it maintains the Earth’s average temperature fairly constant throughout the day and throughout the whole year.

Thus, the atmosphere guarantees that Earth receives the appropriate quantity of heat. It regulates and ensures the survival of living creatures.

Winds : The Movement Of Air : Winds are caused by changes in our atmosphere, such as the heating of the air and the creation of water vapours.

Winds are caused by the following atmospheric events:

  1. When solar radiation hits the Earth, the vast majority of it is reflected back (re-radiated) by land and water bodies. Some are absorbed. From below, these reflected solar radiations reach the atmosphere. 

As a result, convection currents form in the air. Because land heats up quicker than water, the air over land would likewise heat up faster than the air above bodies of water.

  1. During the day in coastal regions, the air above the ground becomes more warm and begins to rise. As this air rises, it creates a zone of low pressure. Air flowing over the sea gravitates toward this region of low pressure. 

Winds are created as air moves from one location to another. During the day, the wind would blow from the sea to the land.

  1. Both land and water begin to chill off at night. Due to the fact that water cools more slowly than land, the air over water will be warmer than the air above land. The air over the water will now begin to rise. 

Land air flows to low pressure areas throughout the night, i.e. the wind direction would be from land to sea.

  1. Other elements influencing winds include the Earth’s rotation and the existence of mountain ranges in the route of the winds. Numerous atmospheric phenomena, such as cyclones and thunderstorms, are also created by air movements induced by unequal heating of the atmosphere in various places.

Rain : Rainfall happens as a result of the following atmospheric events:

  1. Solar radiations heat water bodies throughout the day.
  2. As a result, a significant volume of water evaporates. This is emitted into the atmosphere as water vapours. Numerous biological processes also provide a little quantity of water vapour to the atmosphere.
  3. Sunlight also heats the air. It begins ascending with the water vapours. Air expands and cools as it rises. As a result of this cooling, the water vapours in the air condense into small droplets.
  4. Dust and other suspended particles aid in the condensation of water. They serve as a nucleus around which these droplets attach. Clouds are formed when an excessive collection of small droplets of water gathers.
  5. Once the water droplets are produced, they continue to condense and grow in size. When the droplets get large and heavy, they fall like rain. When the air temperature is sufficiently low, precipitation in the form of snow, sleet, or hail may occur.

The patterns of rainfall are determined by the prevailing wind patterns. Rains are mostly transported to significant sections of our nation by the South-West or North-East monsoons. These are generated in certain regions by depressions in the Bay of Bengal.

Air Pollution : Air pollution is defined as a rise in the concentration of harmful or unwanted substances in the air. These unwelcome substances are referred to as air pollutants. Additionally, air pollution may be described as an unfavourable change in the physical, chemical, or biological aspects of the air.

Causes Of Air Pollution

The actions listed below may contribute to air pollution.

  1. Excessive burning of fossil fuels (such as coal and petroleum) results in a high concentration of nitrogen and sulphur oxides (e.g. NO2 and SO2). These oxides react with the moisture in the air, resulting in acid rain. It has a variety of negative consequences, including corrosion of monuments.
  2. For instance, the Taj Mahal is under danger from the Mathura refinery. It generates significant amounts of SO2 and NO2, which contribute to acid rain. Additionally, the combustion of fossil fuels increases the number of suspended particles in the air. These suspended particles may be unburned carbon particles or hydrocarbons.
  3. Numerous businesses send large amounts of toxic gases into the environment, resulting in air pollution.
  4. Additionally, dust contributes to pollution. Its inhalation causes allergic reactions such as asthma and colds.

Effects Of Air Pollution

The following are the impacts of air pollution.

  1. It affects the respiratory system and contributes to the development of diseases such as asthma, lung cancer, and pneumonia.
  2. Pollutant gases cause allergies and irritate the eyes, lungs, and other organs.
  3. Gases such as NO2, SO2, and others dissolve in rain, resulting in acid rain. • High levels of pollutants in the air limit visibility. Smog is formed in cold weather when water condenses out of the air. It is a visible sign of air pollution.
  4. It results in the greenhouse effect, which contributes to global warming.

WATER: A WONDER LIQUID

Water is a limitless natural resource. It covers a substantial portion of the Earth’s surface (both above and below the earth). In the atmosphere, some water occurs in the form of water vapours. The majority of water on the Earth’s surface (in seas and oceans) is salt. At the poles and on snow-covered mountains, freshwater is found as frozen ice caps. Fresh water is also found underground and in rivers, lakes, and ponds.

Importance Of Water For Living Beings

Water is necessary for life to exist because

  1. It acts as a medium for the conduct of all cellular functions.
  2. It is required for the movement of dissolved chemicals from one portion of the body to another.
  3. It helps in the regulation of body temperature.
  4. It is necessary to maintain the body’s salt balance.
  5. Terrestrial living forms need the presence of freshwater. Their systems are unable to handle or eliminate high concentrations of dissolved salts found in salty water. 
  6. All processes occurring inside our bodies and cells occur between substances dissolved in water.

Water Pollution

It is described as a change in the physical, chemical, or biological quality of water that is undesirable. It arises as a result of the introduction of unwanted and harmful substances known as water pollutants into the water. Water pollution has a detrimental effect on living creatures by rendering the water unfit for usage.

Causes Of Water Pollution

  1. With surface run-off rainwater, water dissolves fertilisers and pesticides from agricultural fields. It transports them to nearby bodies of water, where they have a detrimental influence on aquatic life.
  2. Dumping sewage and other pollutants into bodies of water degrades the water’s quality. 
  3. Industries use water for cooling purposes in a variety of processes. Later, this hot water is discharged into bodies of water. This results in sudden variations in the temperature of the waterbody, which has an effect on aquatic organisms’ reproduction.

Effects Of Water Pollution

Polluted water may have a number of detrimental effects on living forms, as shown below:

  1. Addition Of Undesirable Substances To Water Bodies : Fertilizers, pesticides, dirt, sewage, industrial wastes such as heavy metals (mercury and lead), and disease-causing microbes can pollute the water, making it unsuitable for human consumption.
  2. Death Of Flora And Fauna Of Water Bodies : As the quantity of organic waste in water grows, bacteria and other organisms expand rapidly by using the available dissolved oxygen. As a result, the waterbody becomes oxygen-depleted. This deficiency of oxygen ultimately results in the death of fish and other aquatic animals.
  3. Thermal Pollution Or Change In Temperature : Sudden and significant changes in the temperature range of the waterbody in which aquatic organisms live might be dangerous to them or have a negative impact on their reproductive health. Temperature variations are especially damaging to eggs and larvae.
  4. Human Diseases : Water serves as a home for pathogens, which cause human diseases. Viruses, bacteria, fungus, nematodes, and protozoans are all examples of pathogens. They are responsible for human diseases such as typhoid, cholera, and jaundice.

SOIL

It is the component of the Earth’s outermost layer (crust) that provides support for plant development. Minerals in soil provide a range of nutrients to living organisms. It is a vital resource that determines the variety of life in a given region.

Formation Of Soil 

Soil takes a long time to develop. Throughout hundreds and millions of years, different physical, chemical, and biological processes degrade the rocks at or near the Earth’s surface. The eventual result of this breakdown is the formation of fine soil particles.

Factors Responsible For The Soil Formation

The following elements contribute to soil formation:

  1. Sun : During the day, the Sun warms the rocks, causing them to expand. These rocks cool and contract during the night. Due to the fact that not all portions of rock expand and contract at the same pace, fractures occur. Eventually, the massive boulders break into smaller fragments.
  2. Water : It contributes to soil formation in two ways. 
    1. To begin, water might seep through cracks in the rocks caused by the Sun’s uneven warmth. Freezing this water would result in the spreading of cracks in the future.
    2. Second, flowing water dwindles even the hardest rock over time. Rapidly moving water often transports large and small fragments of rock downstream.
    3. These rocks collide with one another. It creates abrasion, which causes the rocks to break into small parts. The water then transports and deposits these particles farther along its route. That is why soil is often discovered at remote locations from its parent rock.
  3. Wind : It has a similar effect as water. Winds erode rocks. It transports sand from one location to another.
  4. Living Organisms : These factors also have a role in the formation of soil.
  • Lichens thrive on the external surfaces of rocks. They produce substances that cause the rock surface to crumble and generate a thin coating of soil.
  • Other small plants, such as mosses, grow on the exposed surfaces of rocks. They contribute to the further breakdown of rocks. 
  • Additionally, the roots of large trees shatter rocks by penetrating deeper into the rock bed (a process known as biological weathering).

CONSTITUENTS OF SOIL

  1. Soil is made of microscopic crushed rock, pieces of decomposing living organisms (humus), and partly decomposed plant and animal matter (detritus). Additionally, it includes a variety of microorganisms. Minerals, air, water, organic matter, and live organisms are the primary elements of soil.
  2. The kind of soil is determined by the average particle size of its particles. The quantity of humus, organic matter, and microscopic organisms in a soil determines its quality. For example, black soil is high in calcium, iron, magnesium, and aluminium, but red soil is high in iron oxides.
    1. Humus is a dark-colored organic substance that has a significant role in determining the structure of the soil. It increases the permeability of the soil and enables water and air to enter further beneath.
    2. The mineral nutrients contained in a given soil vary according to the kind of rock from which it was produced. The nutritional content of a soil, the quantity of humus in it, and the depth of the soil are all important factors in determining which plants will grow on it.
    3. The term “topsoil” refers to the soil’s uppermost layer. Along with soil particles, it includes humus and biological organisms.
    4. The quality of the topsoil is important in determining an area’s biodiversity.

Soil Pollution

Soil pollution occurs when beneficial components of the soil are removed and dangerous pollutants (both solid and liquid) are introduced. It degrades the soil structure by eradicating the microorganisms responsible for nutrient recycling in the soil. 

Additionally, it destroys earthworms, which are necessary for the formation of rich humus. If sustainable measures are not followed, rich soil may quickly become infertile. Modern agricultural techniques are a significant source of soil pollution. They involve the extensive use of pesticides and fertilisers.

These compounds have a detrimental effect on soil fertility.

Soil Erosion

It is the process of the soil’s top fertile layer being removed by strong winds and running water. The cover of vegetation aids in the percolation of water into deeper levels. Additionally, it aids in preventing the loss of topsoil. 

Without this cover, topsoil is likely to be quickly removed. Soil erosion is more prevalent in steep or mountainous areas. If all of the soil is washed away, the underlying rocks become visible. These rocks are quite fertile.

BIOGEOCHEMICAL CYCLES

Biogeochemical cycles are the cyclical exchanges of nutrients between non-living components (soil, rock, air, and water) and living organisms that give the biosphere its dynamic, yet stable, character. This cyclic movement includes the exchange of matter and energy between the biosphere’s many components.

THE WATER CYCLE

  1. Water is constantly exchanged between the air, the ground, the ocean, and living organisms. The water or hydrological cycle refers to the whole process through which water evaporates, falls as rain on land, and then flows back into the sea via rivers.
  2. Not all water that falls on land quickly returns to the sea. A portion of it trickles into the soil and forms part of the underground freshwater reservoir. A portion of this subsurface water is brought to the surface through springs.
  3. It is brought to the surface by humans using wells or tubewells.
  4. Terrestrial animals and plants also use water for a variety of life activities.
  5. Water passes through or over rocks containing soluble minerals as part of the water cycle. Certain minerals are dissolved in water. As a result, rivers transport a large amount of nutrients from the land to the sea. Marine organisms then use these nutrients.

THE NITROGEN CYCLE

It is the cyclical process by which nitrogen transitions from its elemental state in the atmosphere to a simple nitrogenous compound found in soil and water that may enter living organisms and build complex molecules. These complicated molecules are subsequently broken further, releasing nitrogen into the atmosphere.

Nitrogen gas makes about 78 percent of our atmosphere. It is a structural component of all living beings in the form of proteins, amino acids, nucleic acids (DNA and RNA), and some vitamins. It is also a component of a variety of other chemicals, including alkaloids and urea. Thus, nitrogen is a necessary nutrient for all living forms.

Nitrogen Cycle Involves The Following Important Steps 

  • Nitrogen-Fixation : The nitrogen cycle begins with nitrogen fixation. Nitrogen-fixing bacteria convert inert nitrogen molecules to nitrates or nitrites throughout this process. These bacteria may exist independently or in association with certain dicot plants. 

The majority of nitrogen-fixing bacteria are found in legume roots, namely in their root nodules. Physical processes such as lightning may also transform atmospheric nitrogen to soluble nitrates and nitrites. When lightning strikes, the high temperatures and pressures produced in the air convert nitrogen to nitrogen oxides.

These react with water to produce nitric and nitrous acids. They fall to the ground with the rain. These are then used by numerous types of life.

  • Nitrogen Assimilation : It is accomplished by plants. Nitrate and nitrite are absorbed by plants and converted to amino acids. They are utilised in the production of proteins. Other metabolic pathways result in the formation of other complex nitrogen molecules. Animals may get organic nitrogen directly or indirectly from plants.
  • Ammonification : It is the method through which ammonia is produced (a compound of nitrogen). It happens as a result of the decomposition of dead plants and animals.
  • Nitrification : It is the method through which ammonia is produced (a compound of nitrogen). It happens as a result of the decomposition of dead plants and animals.
  • Denitrification : It is the process of converting nitrates or ammonia found in soil to molecular nitrogen (N2) and returning it into the atmosphere.

This is accomplished by the use of microbes such as Pseudomonas.

THE CARBON CYCLE

Carbon exists in a variety of forms on the Earth. Diamond and graphite are the basic forms of it.

Carbon is found in its mixed condition as

  1. Atmospheric carbon dioxide.
  2. Various minerals include carbonate and hydrogen-carbonate salts.
  3. Coal, petroleum, and natural gas are all examples of fossil fuels.
  4. Molecules that include carbon, such as proteins, lipids, nucleic acids, vitamins, and carbohydrates.
  5. Animal endoskeletons and exoskeletons (carbonate salts).

It is absorbed into living organisms by photosynthesis in plants. Photosynthesis occurs when green plants use CO2 and H 20 in the presence of sunshine and chlorophyll.CO 2 is converted to simple carbohydrate throughout this process (glucose). 

As a byproduct, 02 is liberated. These glucose molecules either offer energy for the synthesis of other vital biological molecules or are transformed to other substances. Respiration is the process through which glucose is converted to energy. It releases CO 2 back into the atmosphere. This method may or may not include the utilisation of oxygen.

The additional processes that release CO 2 into the atmosphere are as follows:

  1. Decomposition of decomposing corpses and organic wastes by decomposing organisms. 
  2. Large-scale combustion (burning) of fossil fuels such as coal and petroleum.
  3. Rock weathering and volcanic eruptions

GREENHOUSE EFFECT AND GLOBAL WARMING

Some gases, including carbon dioxide (CO 2), methane (marsh gas), water vapour, and chlorofluorocarbons (CFCs), among others, act as a barrier to the Earth’s heat loss. These gases, when present in the right concentrations in the atmosphere, are responsible for the heating of the Earth’s surface. 

This is referred to as the greenhouse effect. Global warming occurs as a result of an increase in the amount of greenhouse gases in the atmosphere (the enhanced greenhouse effect)

THE OXYGEN CYCLE

Oxygen is a common element, accounting for around 20.95 percent of the atmospheric gases. It is an important part of the majority of biological molecules, including carbohydrates, proteins, nucleic acids, and lipids. It is present in the Earth’s crust as oxides of several metals as well as as carbonate, sulphate, nitrate, and other minerals. It is also found in mixed form in carbon dioxide and water.

The oxygen cycle is responsible for maintaining the atmospheric oxygen level. The oxygen in the atmosphere is reduced via combustion, respiration, and the creation of nitrogen oxides.

Photosynthesis is the only significant activity that returns oxygen to the atmosphere. As a result, green plants provide the majority of the oxygen in the atmosphere.

OZONE LAYER

Ozone is an oxygen triatomic molecule with the formula 03. It is found in the high atmosphere, above the zone containing elemental oxygen (diatomic molecules).

Ozone is a deadly gas that, fortunately, is not stable at the Earth’s surface.

Importance Of Ozone

Ozone produces a thick layer (similar to a shield) in the upper atmosphere, where it absorbs harmful ultraviolet (UV) rays from the Sun.

As a result, these radiations are prevented from reaching the Earth’s surface. It defends life from the harmful effects of ultraviolet rays.

Threat To Ozone Layer

Numerous man-made substances, such as chlorofluorocarbons or CFCs (carbon compounds containing both fluorine and chlorine), penetrate the ozone layer because they are very stable and are not destroyed by biological processes. 

They have an effect on the ozone layer. It has the effect of depleting or decreasing the ozone layer. In 1985, it resulted in the formation of an ozone hole over Antarctica.

NCERT questions & answers from Natural Resources

Question 1.

How is our atmosphere different from the atmosphere of Venus and Mars?

Answer:

Atmosphere over EarthAtmosphere over Venus and Mars
Nitrogen and Oxygen.It contains nitrogen and oxygen.The two are absent
Carbon Dioxide.Carbon dioxide content is little (0-03%).Carbon dioxide is the most common gas in the air, making up 95–97% of the atmosphere.
Water Vapours.The atmosphere contains water vapours which form a component of the water cycle.Water vapour is not present in the atmosphere. As there are no living organisms involved,
living Beings.Living things keep the atmosphere from changing too much.figuring out what gases make up the air we breathe.

Question 2.

How does the atmosphere act as a blanket?

Answer: The atmosphere or air is a bad conductor of heat. It, therefore, functions as a blanket.

  1. It keeps the temperature from rising quickly during the day when the sun is out.
  2. There’s no sudden drop in temperature at night. The atmosphere makes it take longer for heat to leave the dark parts of the earth and go into space.
  3. The average temperature of the Earth stays pretty steady thanks to the atmosphere, both during the day and all year long.

Question 3.

What causes winds?

Answer: Most winds are caused by places where the air is warmer than other places. The warm air goes up. This makes a low-pressure area. This area gets cooler air from areas with higher pressure nearby. The result is wind. Winds move in different directions in different parts of the world because of the following:

  1. Heating of land in different parts of the world at different rates
  2. Differences in how land and water heat and cool.
  3. Mountains make a wall
  4. Earth’s rotation.

Question 4.

How are clouds formed? (CCE 2011)

Answer: Clouds are big masses of wet air that move in the direction of the wind. When there are a lot of water vapours, they form. Since water bodies and wet areas heat up during the day, water evaporates from their surfaces. Plants also give off water vapour through a process called transpiration. Animals do the same thing when they breathe out or sweat. During the day, the air also gets hotter. The hot air and water vapour both rise. When air rises, it gets bigger and cooler. The water vapour condenses when the temperature drops. Dust and other particles in the air act as centres around which water vapour condenses. Clouds are made when a large mass of wet air comes together.

Question 5.

Answer:  List any three human activities that you think would lead to air pollution.

  1. fossil fuels being burned in factories, cars, and power plants.
  2. Industries like textiles, asbestos, and flour mills all need to be processed.
  3. Crushing stones.

Question 6.

Why do organisms need water? (CCE 2011)

Answer:

Organisms need water due to following reasons :

  1. Part of Living Matter: Water makes up 60–90% of living things.
  2. Solvent: Water is a common solvent for chemicals found in the living world.
  3. Reaction Medium: All biochemical reactions take place in water.
  4. Transport: Substances can only be moved through the body of a living thing in a dissolved state.
  5. Turgidity: Cells, cell organelles, tissues, and other structures only keep their shape when they contain enough water to make them turgid.
  6. Temperature buffer: Water protects the body from sudden changes in temperature.
  7. Wastes: It helps to separate and get rid of metabolic wastes.

Question 7.

What is the major source of fresh water in the city/town/village where you live?

Answer: Groundwater which is pumped out by tube wells (In some it is a local reservoir, canal or river.

Question 8.

Do you know of any activity which may be polluting this water source?

Answer: Putting industrial waste where pollutants seep into the ground and end up in groundwater (sewage and industrial effluents in case of canal or river water).

Question 9.

How is soil formed? What is the function of humps in soil ? (CCE 2011, 2012)

Answer: Soil is formed through two processes of weathering and humification.

Weathering

It is the process of grinding or breaking rocks into small pieces. There are three types of weathering: physical, chemical, and biological. Physical weathering is caused by changes in the atmosphere and mechanical forces. They are done by the sun, the water, the wind, and living things.

  • Sun: By heating, it causes rocks to get bigger. When it gets cooler, they get smaller. Rocks grow and shrink at different rates in different places. When rocks expand and contract in different ways, they crack and break up.
  • Water:
  • Wetting and Drying: Some parts of rocks can absorb and release water. They get bigger and smaller, which causes rocks to break up.
  • Frost Action: If it gets cold enough for the water to freeze, it will swell up and put a lot of pressure on the cracks. The rock would break into pieces.
  • Abrasion: Running water carrying pieces of rock would break and grind rocks in the way. Rain and hail can also break up rocks.
  • Wind: When the wind hits a rock, dust and fine sand carried by the wind wear away the rock’s surface.
  • Living Organisms: Lichens release chemicals that break up minerals on the surface of rocks. This makes spaces where dust can gather. There, mosses grow. They cause cracks to get bigger and crevices to get deeper. Roots of plants that don’t last long make these cracks bigger. Rocks break up because the roots of bigger plants grow into cracks and get bigger.

Humification

Soil is made when humus, which is partially broken down organic matter, mixes with pieces of weathered rock. Humus helps make soil crumbs, which are important for keeping the soil moist and letting air in.

Question 10.

What are the methods of preventing or reducing soil erosion?

Answer:

Soil Erosion: It is when wind or water takes away the top layer of soil. Wind and water also break down rocks and move the small pieces to other places, where they mix with other materials to make soil. When water or wind wash away the top layer of soil, the subsoil and rocky base below are shown. There aren’t many plants that can grow there.

Factors Promoting Soil Erosion

  1. It kills herbs, grasses, and young plants. The soil can be seen. When animals walk on the soil, they compact it, which makes it less porous and less able to let water through.
  2. When the trash is picked up or the forest floor is scraped, the ground is left open to actions that cause erosion.
  3. There is less water absorption because water doesn’t stay on the slope for long. As water flows down a slope, it picks up speed and can cut through more things and carry more water.
  4. Cutting Down Trees: Cutting down more trees than a forest can grow back causes deforestation. It also leaves a lot of space open for wind and water to move through. When trees are cut down or a forest is cleared, not only is biodiversity lost but large amounts of soil are washed away.
  5. Clean Tilling: When crop fields are tilled in a clean way, the soil is more likely to wash away.
  6. Strong winds and a lot of rain. Soil that isn’t covered quickly wears away by heavy rain and strong winds.

Question 11.

What are two different states in which water is found during the water cycle?

Answer: Liquid and vapour, occasionally solid (snow) as well.

Question 12.

Name two biologically important compounds that contain both oxygen and nitrogen. (CCE 2014)

Answer: Proteins and nucleic acids.

Question 13.

List any three human activities which would lead to an increase in the carbon dioxide content of air.

Answer:

  1. More fossil fuels (coal, oil, and natural gas) are being burned in homes, businesses, transportation, and power projects.
  2. Using wood for cooking and heating more often.
  3. Carbon dioxide is used less in photosynthesis when trees are cut down.

Question 14.

What is the greenhouse effect? (CCE 2011, 2012, 2013)

Answer: The greenhouse effect keeps a place warm by letting solar radiation in but stopping long waves from getting out. This is because there are radiatively active gases and glass panes in the area.

Question 15.

What are the two forms of oxygen found in the atmosphere? (CCE 2011, 2014)

Answer:

  1. Diatomic oxygen, O2
  2. Triatomic oxygen or ozone, O3.
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