Knowt
Chapter 14-Natural Resources
What are these resources on the Earth?
These are the land, the water and the air.
The outer crust of the Earth is called the lithosphere
Water covers 75% of the Earth’s surface. It is also found underground. These comprise the hydrosphere.
The air that covers the whole of the Earth like a blanket, is called the atmosphere.
Living things are found where these three exist. This life-supporting zone of the Earth where the atmosphere, the hydrosphere and the lithosphere interact and make life possible, is known as the biosphere.
The biosphere is the region of the Earth that supports life and is where the interactions between the hydrosphere, lithosphere, and atmosphere occur.
Living things constitute the biotic component of the biosphere.
The air, the water and the soil form the non-living or abiotic component of the biosphere.
The Breath of Life: Air
It is a mixture of many gases like nitrogen, oxygen, carbon dioxide and water vapour
Eukaryotic cells and many prokaryotic cells, need oxygen to break down glucose molecules and get energy for their activities. This results in the production of carbon dioxide.
Another process which results in the consumption of oxygen and the concomitant production of carbon dioxide is combustion. This includes not just human activities, which burn fuels to get energy, but also forest fires.
Despite this, the percentage of carbon dioxide in our atmosphere is a mere fraction of a percent because carbon dioxide is ‘fixed’ in two ways:
In the presence of sunlight, green plants convert carbon dioxide into glucose.
Many marine animals use carbonates dissolved in sea-water to make their shells.
THE ROLE OF THE ATMOSPHERE IN CLIMATE CONTROL
Air is a bad conductor of heat. The atmosphere keeps the average temperature of the Earth fairly steady during the day and even during the course of the whole year
The atmosphere prevents the sudden increase in temperature during the daylight hours.
During the night, it slows down the escape of heat into outer space. Think of the moon, which is about the same distance from the Sun that the Earth is. Despite that, on the surface of the moon, with no atmosphere, the temperature ranges from –190° C to 110° C.
THE MOVEMENT OF AIR: WINDS
We have all felt the relief brought by cool evening breezes after a hot day.
All these phenomena are the result of changes that take place in our atmosphere due to the heating of air and the formation of water vapour.
Water vapour is formed due to the heating of water bodies and the activities of living organisms.The atmosphere can be heated from below by the radiation that is reflected back or re-radiated by the land or water bodies.On being heated, convection currents are set up in the air.
land breeze and sea breeze
Air rises when it is heated by radiation from hot land or water. However, since land warms up more quickly than water, air above land would similarly warm up more quickly than air above bodies of water.
Sea Breeze
If we look at the situation in coastal regions during the day, the air above the land gets heated faster and starts rising.
As this air rises, a region of low pressure is created and air over the sea moves into this area of low pressure.
The movement of air from one region to the other creates winds. During the day, the direction of the wind would be from the sea to the land.
Land Breeze
Land Breeze is the breeze that blows from land to sea
At night, the surface cools more quickly than the sea surface. Warmer air over the water rises as a result. In order to replenish the warm air, the denser cool air over the land is migrating offshore.
IMPORTANT- all the movements of air resulting in diverse atmospheric phenomena are caused by the uneven heating of the atmosphere in different regions of the Earth. But various other factors also influence these winds – the rotation of the Earth and the presence of mountain ranges in the paths of the wind are a couple of these factors.For instance,presence of the Himalayas change the flow of a wind blowing from Allahabad towards the north
RAIN
When water bodies are heated during the day, a large amount of water evaporates and goes into the air
Some amount of water vapour also get into the atmosphere because of various biological activities. This air also gets heated. The hot air rises up carrying the water vapour with it.
As the air rises, it expands and cools. This cooling causes the water vapour in the air to condense in the form of tiny droplets.
This condensation of water is facilitated if some particles could act as the ‘nucleus’ for these drops to form around. Normally dust and other suspended particles in the air perform this function.
Once the water droplets are formed, they grow bigger by the ‘condensation’ of these water droplets. When the drops have grown big and heavy, they fall down in the form of rain.
Sometimes, when the temperature of air is low enough, precipitation may occur in the form of snow, sleet or hail.
Rainfall patterns are decided by the prevailing wind patterns. In large parts of India, rains are mostly brought by the southwest or north-east monsoons. We have also heard weather reports that say ‘depressions’ in the Bay of Bengal have caused rains in some areas
AIR POLLUTION
An increase in the content of these harmful substances in air is called air pollution
The fossil fuels like coal and petroleum contain small amounts of nitrogen and sulphur. When these fuels are burnt, nitrogen and sulphur too are burnt and this produces different oxides of nitrogen and sulphur
Not only is the inhalation of these gases dangerous, they also dissolve in rain to give rise to acid rain
The combustion of fossil fuels also increases the amount of suspended particles in air. These suspended particles could be unburnt carbon particles or substances called hydrocarbons.
Presence of high levels of all these pollutants cause visibility to be lowered, especially in cold weather when water also condenses out of air. This is known as smog and is a visible indication of air pollution.
Studies have shown that regularly breathing air that contains any of these substances increases the incidence of allergies, cancer and heart diseases.
Water: A Wonder Liquid
sources of water
Water occupies a very large area of the Earth’s surface and is also found underground. Some amount of water exists in the form of water vapour in the atmosphere.
Most of the water on Earth’s surface is found in seas and oceans and is saline.
Fresh water is found frozen in the ice-caps at the two poles and on snow covered mountains.
The underground water and the water in rivers, lakes and ponds is also fresh
why is water so necessary?
All cellular processes take place in a water medium.
All the reactions that take place within our body and within the cells occur between substances that are dissolved in water.
Substances are also transported from one part of the body to the other in a dissolved form
Terrestrial life-forms require fresh water for this because their bodies cannot tolerate or get rid of the high amounts of dissolved salts in saline water.
WATER POLLUTION
The addition of undesirable substances to water -bodies. These substances could be the fertilisers and pesticides used in farming or they could be poisonous substances, like mercury salts which are used by paper-industries. These could also be disease-causing organisms, like the bacteria which cause cholera.
The removal of desirable substances from water-bodies. Dissolved oxygen is used by the animals and plants that live in water. Any change that reduces the amount of this dissolved oxygen would adversely affect these aquatic organisms. Other nutrients could also be depleted from the water bodies.
A change in temperature. Aquatic organisms are used to a certain range of temperature in the water -body where they live, and a sudden marked change in this temperature would be dangerous for them or affect their breeding. The eggs and larvae of various animals are particularly susceptible to temperature changes.
Water dissolves the fertilisers and pesticides that we use on our farms. So some percentage of these substances are washed into the water bodies
Sewage from our towns and cities and the waste from factories are also dumped into rivers or lakes.
Specific industries also use water for cooling in various operations and later return this hot water to water-bodies.
Another manner in which the temperature of the water in rivers can be affected is when water is released from dams. The water inside the deep reservoir would be colder than the water at the surface which gets heated by the Sun.
Mineral Riches in the Soil
How soil is formed?
The outermost layer of our Earth is called the crust and the minerals found in this layer supply a variety of nutrients to life-forms.
But these minerals will not be available to the organisms if the minerals are bound up in huge rocks.
Over long periods of time, thousands and millions of years, the rocks at or near the surface of the Earth are broken down by various physical, chemical and some biological processes.
The end product of this breaking down is the fine particles of soil
But what are the factors or processes that make soil?
The Sun:
The Sun heats up rocks during the day so that they expand.
At night, these rocks cool down and contract. Since all parts of the rock do not expand and contract at the same rate, this results in the formation of cracks and ultimately the huge rocks break up into smaller pieces.
Water: Water helps in the formation of soil in two ways.
One, water could get into the cracks in the rocks formed due to uneven heating by the Sun. If this water later freezes, it would cause the cracks to widen.
Two, flowing water wears away even hard rock over long periods of time. Fast flowing water often carries big and small particles of rock downstream. These rocks rub against other rocks and the resultant abrasion causes the rocks to wear down into smaller and smaller particles. The water then takes these particles along with it and deposits it further down its path. Soil is thus found in places far away from its parent-rock.
Wind: In a process similar to the way in which water rubs against rocks and wears them down, strong winds also erode rocks down. The wind also carries sand from one place to the other like water does.
Living organisms also influence the formation of soil.
The lichen that we read about earlier, also grows on the surface of rocks.
While growing, they release certain substances that cause the rock surface to powder down and form a thin layer of soil. Other small plants like moss, are able to grow on this surface now and they cause the rock to break up further.
The roots of big trees sometimes go into cracks in the rocks and as the roots grow bigger, the crack is forced bigger
The type of soil is decided by the average size of particles found in it and the quality of the soil is decided by the amount of humus and the microscopic organisms found in it. Humus is a major factor in deciding the soil structure because it causes the soil to become more porous and allows water and air to penetrate deep underground.
The factors that decide which plants will thrive on that soil.
On the rocks it was formed from.
The nutrient content of a soil,
The amount of humus present in it
The depth of the soil
The topmost layer of the soil that contains humus and living organisms in addition to the soil particles is called the topsoil. The quality of the topsoil is an important factor that decides biodiversity in that area.
The roots of plants have an important role in preventing soil erosion.
The large-scale deforestation that is happening all over the world not only destroys biodiversity, it also leads to soil erosion.
Topsoil that is bare of vegetation, is likely to be removed very quickly. And this is accelerated in hilly or mountainous regions.
This process of soil erosion is very difficult to reverse. Vegetative cover on the ground has a role to play in the percolation of water into the deeper layers too.
THE WATER-CYCLE
The water evaporates from the water bodies and subsequent condensation of this water vapour leads to rain. But we don’t see the seas and oceans drying up. So, how is the water returning to these water bodies? The whole process in which water evaporates and falls on the land as rain and later flows back into the sea via rivers is known as the water-cycle.
All of the water that falls on the land does not immediately flow back into the sea.
Some of it seeps into the soil and becomes part of the underground reservoir of fresh-water.
Some of this underground water finds its way to the surface through springs.
Or we bring it to the surface for our use through wells or tubewells.
THE NITROGEN-CYCLE
Nitrogen gas makes up 78% of our atmosphere and nitrogen is also a part of many molecules essential to life like proteins, nucleic acids (DNA and RNA) and some vitamins.
Nitrogen is found in other biologically important compounds such as alkaloids and urea too. Nitrogen is thus an essential nutrient for all life-forms and life would be simple if all these life-forms could use the atmospheric nitrogen directly.
Other than a few forms of bacteria, life-forms are not able to convert the comparatively inert nitrogen molecule into forms like nitrates and nitrites which can be taken up and used to make the required molecules.
These ‘nitrogen-fixing’ bacteria may be free-living or be associated with some species of dicot plants. Most commonly, the nitrogen-fixing bacteria are found in the roots of legumes (generally the plants which give us pulses) in special structures called root nodules.
Other than these bacteria, the only other manner in which the nitrogen molecule is converted to nitrates and nitrites is by a physical process.
During lightning, the high temperatures and pressures created in the air convert nitrogen into oxides of nitrogen.
These oxides dissolve in water to give nitric and nitrous acids and fall on land along with rain. These are then utilised by various lifeforms.
What happens to the nitrogen once it is converted into forms that can be taken up and used to make nitrogen-containing molecules?
Plants generally take up nitrates and nitrites and convert them into amino acids which are used to make proteins.
Some other biochemical pathways are used to make the other complex compounds containing nitrogen.
These proteins and other complex compounds are subsequently consumed by animals.
Once the animal or the plant dies, other bacteria in the soil convert the various compounds of nitrogen back into nitrates and nitrites.
A different type of bacteria converts the nitrates and nitrites into elemental nitrogen.
Thus, there is a nitrogen-cycle in nature in which nitrogen passes from its elemental form in the atmosphere into simple molecules in the soil and water, which get converted to more complex molecules in living beings and back again to the simple nitrogen molecule in the atmosphere.
THE CARBON-CYCLE
CARBON
Carbon is found in various forms on the Earth. It occurs in the elemental form as diamonds and graphite.
In the combined state, it is found as carbon dioxide in the atmosphere, as carbonate and hydrogencarbonate salts in various minerals, while all life-forms are based on carbon-containing molecules like proteins, carbohydrates, fats,nucleic acids and vitamins.
CARBON-CYCLE
The endoskeletons and exoskeletons of various animals are also formed from carbonate salts. Carbon is incorporated into life-forms through the basic process of photosynthesis which is performed in the presence of Sunlight by all life-forms that contain chlorophyll.
This process converts carbon dioxide from the atmosphere or dissolved in water into glucose molecules.
These glucose molecules are either converted into other substances or used to provide energy for the synthesis of other biologically important molecules.
The utilisation of glucose to provide energy to living things involves the process of respiration in which oxygen may or may not be used to convert glucose back into carbon dioxide.
This carbon dioxide then goes back into the atmosphere.
Another process that adds to the carbon dioxide in the atmosphere is the process of combustion where fuels are burnt to provide energy for various needs like heating, cooking, transportation and industrial processes.
In fact, the percentage of carbon dioxide in the atmosphere is said to have doubled since the industrial revolution when human beings started burning fossil fuels on a very large scale.
Carbon, like water, is thus cycled repeatedly through different forms by the various physical and biological activities.
THE GREENHOUSE EFFECT
An increase in the percentage of such gases in the atmosphere would cause the average temperatures to increase world-wide and this is called the greenhouse effect.
Carbon dioxide is one of the greenhouse gases.
An increase in the carbon dioxide content in the atmosphere would cause more heat to be retained by the atmosphere and lead to global warming.
THE OXYGEN-CYCLE
When we talk of the oxygen-cycle, we are mainly referring to the cycle that maintains the levels of oxygen in the atmosphere.
Oxygen from the atmosphere is used up in three processes, namely combustion, respiration and in the formation of oxides of nitrogen.
Oxygen is returned to the atmosphere in only one major process, that is, photosynthesis. And this forms the broad outline of the oxygen-cycle in nature bacteria, are poisoned by elemental oxygen. In fact, even the process of nitrogen-fixing by bacteria does not take place in the presence of oxygen.
Ozone Layer
Elemental oxygen is normally found in the form of a diatomic molecule.
However, in the upper reaches of the atmosphere, a molecule containing three atoms of oxygen is found. This would mean a formula of O3 and this is called ozone.
Unlike the normal diatomic molecule of oxygen, ozone is poisonous and we are lucky that it is not stable nearer to the Earth’s surface.
But it performs an essential function where it is found. It absorbs harmful radiations from the Sun.
This prevents those harmful radiations from reaching the surface of the Earth where they may damage many forms of life.
Ozone Layer depletion
Recently it was discovered that this ozone layer was getting depleted. Various man-made compounds like CFCs (carbon compounds having both fluorine and chlorine which are very stable and not degraded by any biological process) were found to persist in the atmosphere.
Once they reached the ozone layer, they would react with the ozone molecules.
This resulted in a reduction of the ozone layer and recently they have discovered a hole in the ozone layer above the Antartica.
It is difficult to imagine the consequences for life on Earth if the ozone layer dwindles further, but many people think that it would be better not to take chances. These people advocate working towards stopping all further damage to the ozone layer
Chapter 14-Natural Resources
What are these resources on the Earth?
These are the land, the water and the air.
The outer crust of the Earth is called the lithosphere
Water covers 75% of the Earth’s surface. It is also found underground. These comprise the hydrosphere.
The air that covers the whole of the Earth like a blanket, is called the atmosphere.
Living things are found where these three exist. This life-supporting zone of the Earth where the atmosphere, the hydrosphere and the lithosphere interact and make life possible, is known as the biosphere.
The biosphere is the region of the Earth that supports life and is where the interactions between the hydrosphere, lithosphere, and atmosphere occur.
Living things constitute the biotic component of the biosphere.
The air, the water and the soil form the non-living or abiotic component of the biosphere.
The Breath of Life: Air
It is a mixture of many gases like nitrogen, oxygen, carbon dioxide and water vapour
Eukaryotic cells and many prokaryotic cells, need oxygen to break down glucose molecules and get energy for their activities. This results in the production of carbon dioxide.
Another process which results in the consumption of oxygen and the concomitant production of carbon dioxide is combustion. This includes not just human activities, which burn fuels to get energy, but also forest fires.
Despite this, the percentage of carbon dioxide in our atmosphere is a mere fraction of a percent because carbon dioxide is ‘fixed’ in two ways:
In the presence of sunlight, green plants convert carbon dioxide into glucose.
Many marine animals use carbonates dissolved in sea-water to make their shells.
THE ROLE OF THE ATMOSPHERE IN CLIMATE CONTROL
Air is a bad conductor of heat. The atmosphere keeps the average temperature of the Earth fairly steady during the day and even during the course of the whole year
The atmosphere prevents the sudden increase in temperature during the daylight hours.
During the night, it slows down the escape of heat into outer space. Think of the moon, which is about the same distance from the Sun that the Earth is. Despite that, on the surface of the moon, with no atmosphere, the temperature ranges from –190° C to 110° C.
THE MOVEMENT OF AIR: WINDS
We have all felt the relief brought by cool evening breezes after a hot day.
All these phenomena are the result of changes that take place in our atmosphere due to the heating of air and the formation of water vapour.
Water vapour is formed due to the heating of water bodies and the activities of living organisms.The atmosphere can be heated from below by the radiation that is reflected back or re-radiated by the land or water bodies.On being heated, convection currents are set up in the air.
land breeze and sea breeze
Air rises when it is heated by radiation from hot land or water. However, since land warms up more quickly than water, air above land would similarly warm up more quickly than air above bodies of water.
Sea Breeze
If we look at the situation in coastal regions during the day, the air above the land gets heated faster and starts rising.
As this air rises, a region of low pressure is created and air over the sea moves into this area of low pressure.
The movement of air from one region to the other creates winds. During the day, the direction of the wind would be from the sea to the land.
Land Breeze
Land Breeze is the breeze that blows from land to sea
At night, the surface cools more quickly than the sea surface. Warmer air over the water rises as a result. In order to replenish the warm air, the denser cool air over the land is migrating offshore.
IMPORTANT- all the movements of air resulting in diverse atmospheric phenomena are caused by the uneven heating of the atmosphere in different regions of the Earth. But various other factors also influence these winds – the rotation of the Earth and the presence of mountain ranges in the paths of the wind are a couple of these factors.For instance,presence of the Himalayas change the flow of a wind blowing from Allahabad towards the north
RAIN
When water bodies are heated during the day, a large amount of water evaporates and goes into the air
Some amount of water vapour also get into the atmosphere because of various biological activities. This air also gets heated. The hot air rises up carrying the water vapour with it.
As the air rises, it expands and cools. This cooling causes the water vapour in the air to condense in the form of tiny droplets.
This condensation of water is facilitated if some particles could act as the ‘nucleus’ for these drops to form around. Normally dust and other suspended particles in the air perform this function.
Once the water droplets are formed, they grow bigger by the ‘condensation’ of these water droplets. When the drops have grown big and heavy, they fall down in the form of rain.
Sometimes, when the temperature of air is low enough, precipitation may occur in the form of snow, sleet or hail.
Rainfall patterns are decided by the prevailing wind patterns. In large parts of India, rains are mostly brought by the southwest or north-east monsoons. We have also heard weather reports that say ‘depressions’ in the Bay of Bengal have caused rains in some areas
AIR POLLUTION
An increase in the content of these harmful substances in air is called air pollution
The fossil fuels like coal and petroleum contain small amounts of nitrogen and sulphur. When these fuels are burnt, nitrogen and sulphur too are burnt and this produces different oxides of nitrogen and sulphur
Not only is the inhalation of these gases dangerous, they also dissolve in rain to give rise to acid rain
The combustion of fossil fuels also increases the amount of suspended particles in air. These suspended particles could be unburnt carbon particles or substances called hydrocarbons.
Presence of high levels of all these pollutants cause visibility to be lowered, especially in cold weather when water also condenses out of air. This is known as smog and is a visible indication of air pollution.
Studies have shown that regularly breathing air that contains any of these substances increases the incidence of allergies, cancer and heart diseases.
Water: A Wonder Liquid
sources of water
Water occupies a very large area of the Earth’s surface and is also found underground. Some amount of water exists in the form of water vapour in the atmosphere.
Most of the water on Earth’s surface is found in seas and oceans and is saline.
Fresh water is found frozen in the ice-caps at the two poles and on snow covered mountains.
The underground water and the water in rivers, lakes and ponds is also fresh
why is water so necessary?
All cellular processes take place in a water medium.
All the reactions that take place within our body and within the cells occur between substances that are dissolved in water.
Substances are also transported from one part of the body to the other in a dissolved form
Terrestrial life-forms require fresh water for this because their bodies cannot tolerate or get rid of the high amounts of dissolved salts in saline water.
WATER POLLUTION
The addition of undesirable substances to water -bodies. These substances could be the fertilisers and pesticides used in farming or they could be poisonous substances, like mercury salts which are used by paper-industries. These could also be disease-causing organisms, like the bacteria which cause cholera.
The removal of desirable substances from water-bodies. Dissolved oxygen is used by the animals and plants that live in water. Any change that reduces the amount of this dissolved oxygen would adversely affect these aquatic organisms. Other nutrients could also be depleted from the water bodies.
A change in temperature. Aquatic organisms are used to a certain range of temperature in the water -body where they live, and a sudden marked change in this temperature would be dangerous for them or affect their breeding. The eggs and larvae of various animals are particularly susceptible to temperature changes.
Water dissolves the fertilisers and pesticides that we use on our farms. So some percentage of these substances are washed into the water bodies
Sewage from our towns and cities and the waste from factories are also dumped into rivers or lakes.
Specific industries also use water for cooling in various operations and later return this hot water to water-bodies.
Another manner in which the temperature of the water in rivers can be affected is when water is released from dams. The water inside the deep reservoir would be colder than the water at the surface which gets heated by the Sun.
Mineral Riches in the Soil
How soil is formed?
The outermost layer of our Earth is called the crust and the minerals found in this layer supply a variety of nutrients to life-forms.
But these minerals will not be available to the organisms if the minerals are bound up in huge rocks.
Over long periods of time, thousands and millions of years, the rocks at or near the surface of the Earth are broken down by various physical, chemical and some biological processes.
The end product of this breaking down is the fine particles of soil
But what are the factors or processes that make soil?
The Sun:
The Sun heats up rocks during the day so that they expand.
At night, these rocks cool down and contract. Since all parts of the rock do not expand and contract at the same rate, this results in the formation of cracks and ultimately the huge rocks break up into smaller pieces.
Water: Water helps in the formation of soil in two ways.
One, water could get into the cracks in the rocks formed due to uneven heating by the Sun. If this water later freezes, it would cause the cracks to widen.
Two, flowing water wears away even hard rock over long periods of time. Fast flowing water often carries big and small particles of rock downstream. These rocks rub against other rocks and the resultant abrasion causes the rocks to wear down into smaller and smaller particles. The water then takes these particles along with it and deposits it further down its path. Soil is thus found in places far away from its parent-rock.
Wind: In a process similar to the way in which water rubs against rocks and wears them down, strong winds also erode rocks down. The wind also carries sand from one place to the other like water does.
Living organisms also influence the formation of soil.
The lichen that we read about earlier, also grows on the surface of rocks.
While growing, they release certain substances that cause the rock surface to powder down and form a thin layer of soil. Other small plants like moss, are able to grow on this surface now and they cause the rock to break up further.
The roots of big trees sometimes go into cracks in the rocks and as the roots grow bigger, the crack is forced bigger
The type of soil is decided by the average size of particles found in it and the quality of the soil is decided by the amount of humus and the microscopic organisms found in it. Humus is a major factor in deciding the soil structure because it causes the soil to become more porous and allows water and air to penetrate deep underground.
The factors that decide which plants will thrive on that soil.
On the rocks it was formed from.
The nutrient content of a soil,
The amount of humus present in it
The depth of the soil
The topmost layer of the soil that contains humus and living organisms in addition to the soil particles is called the topsoil. The quality of the topsoil is an important factor that decides biodiversity in that area.
The roots of plants have an important role in preventing soil erosion.
The large-scale deforestation that is happening all over the world not only destroys biodiversity, it also leads to soil erosion.
Topsoil that is bare of vegetation, is likely to be removed very quickly. And this is accelerated in hilly or mountainous regions.
This process of soil erosion is very difficult to reverse. Vegetative cover on the ground has a role to play in the percolation of water into the deeper layers too.
THE WATER-CYCLE
The water evaporates from the water bodies and subsequent condensation of this water vapour leads to rain. But we don’t see the seas and oceans drying up. So, how is the water returning to these water bodies? The whole process in which water evaporates and falls on the land as rain and later flows back into the sea via rivers is known as the water-cycle.
All of the water that falls on the land does not immediately flow back into the sea.
Some of it seeps into the soil and becomes part of the underground reservoir of fresh-water.
Some of this underground water finds its way to the surface through springs.
Or we bring it to the surface for our use through wells or tubewells.
THE NITROGEN-CYCLE
Nitrogen gas makes up 78% of our atmosphere and nitrogen is also a part of many molecules essential to life like proteins, nucleic acids (DNA and RNA) and some vitamins.
Nitrogen is found in other biologically important compounds such as alkaloids and urea too. Nitrogen is thus an essential nutrient for all life-forms and life would be simple if all these life-forms could use the atmospheric nitrogen directly.
Other than a few forms of bacteria, life-forms are not able to convert the comparatively inert nitrogen molecule into forms like nitrates and nitrites which can be taken up and used to make the required molecules.
These ‘nitrogen-fixing’ bacteria may be free-living or be associated with some species of dicot plants. Most commonly, the nitrogen-fixing bacteria are found in the roots of legumes (generally the plants which give us pulses) in special structures called root nodules.
Other than these bacteria, the only other manner in which the nitrogen molecule is converted to nitrates and nitrites is by a physical process.
During lightning, the high temperatures and pressures created in the air convert nitrogen into oxides of nitrogen.
These oxides dissolve in water to give nitric and nitrous acids and fall on land along with rain. These are then utilised by various lifeforms.
What happens to the nitrogen once it is converted into forms that can be taken up and used to make nitrogen-containing molecules?
Plants generally take up nitrates and nitrites and convert them into amino acids which are used to make proteins.
Some other biochemical pathways are used to make the other complex compounds containing nitrogen.
These proteins and other complex compounds are subsequently consumed by animals.
Once the animal or the plant dies, other bacteria in the soil convert the various compounds of nitrogen back into nitrates and nitrites.
A different type of bacteria converts the nitrates and nitrites into elemental nitrogen.
Thus, there is a nitrogen-cycle in nature in which nitrogen passes from its elemental form in the atmosphere into simple molecules in the soil and water, which get converted to more complex molecules in living beings and back again to the simple nitrogen molecule in the atmosphere.
THE CARBON-CYCLE
CARBON
Carbon is found in various forms on the Earth. It occurs in the elemental form as diamonds and graphite.
In the combined state, it is found as carbon dioxide in the atmosphere, as carbonate and hydrogencarbonate salts in various minerals, while all life-forms are based on carbon-containing molecules like proteins, carbohydrates, fats,nucleic acids and vitamins.
CARBON-CYCLE
The endoskeletons and exoskeletons of various animals are also formed from carbonate salts. Carbon is incorporated into life-forms through the basic process of photosynthesis which is performed in the presence of Sunlight by all life-forms that contain chlorophyll.
This process converts carbon dioxide from the atmosphere or dissolved in water into glucose molecules.
These glucose molecules are either converted into other substances or used to provide energy for the synthesis of other biologically important molecules.
The utilisation of glucose to provide energy to living things involves the process of respiration in which oxygen may or may not be used to convert glucose back into carbon dioxide.
This carbon dioxide then goes back into the atmosphere.
Another process that adds to the carbon dioxide in the atmosphere is the process of combustion where fuels are burnt to provide energy for various needs like heating, cooking, transportation and industrial processes.
In fact, the percentage of carbon dioxide in the atmosphere is said to have doubled since the industrial revolution when human beings started burning fossil fuels on a very large scale.
Carbon, like water, is thus cycled repeatedly through different forms by the various physical and biological activities.
THE GREENHOUSE EFFECT
An increase in the percentage of such gases in the atmosphere would cause the average temperatures to increase world-wide and this is called the greenhouse effect.
Carbon dioxide is one of the greenhouse gases.
An increase in the carbon dioxide content in the atmosphere would cause more heat to be retained by the atmosphere and lead to global warming.
THE OXYGEN-CYCLE
When we talk of the oxygen-cycle, we are mainly referring to the cycle that maintains the levels of oxygen in the atmosphere.
Oxygen from the atmosphere is used up in three processes, namely combustion, respiration and in the formation of oxides of nitrogen.
Oxygen is returned to the atmosphere in only one major process, that is, photosynthesis. And this forms the broad outline of the oxygen-cycle in nature bacteria, are poisoned by elemental oxygen. In fact, even the process of nitrogen-fixing by bacteria does not take place in the presence of oxygen.
Ozone Layer
Elemental oxygen is normally found in the form of a diatomic molecule.
However, in the upper reaches of the atmosphere, a molecule containing three atoms of oxygen is found. This would mean a formula of O3 and this is called ozone.
Unlike the normal diatomic molecule of oxygen, ozone is poisonous and we are lucky that it is not stable nearer to the Earth’s surface.
But it performs an essential function where it is found. It absorbs harmful radiations from the Sun.
This prevents those harmful radiations from reaching the surface of the Earth where they may damage many forms of life.
Ozone Layer depletion
Recently it was discovered that this ozone layer was getting depleted. Various man-made compounds like CFCs (carbon compounds having both fluorine and chlorine which are very stable and not degraded by any biological process) were found to persist in the atmosphere.
Once they reached the ozone layer, they would react with the ozone molecules.
This resulted in a reduction of the ozone layer and recently they have discovered a hole in the ozone layer above the Antartica.
It is difficult to imagine the consequences for life on Earth if the ozone layer dwindles further, but many people think that it would be better not to take chances. These people advocate working towards stopping all further damage to the ozone layer
