Nitrogen Cycle Explained – Types of Nitrogen Fixation

Nitrogen Cycle is a biogeochemical

process which transforms the inert
nitrogen present in the atmosphere to
a more usable form for living
NITROGEN Stages of Nitrogen Cycle
Process of the Nitrogen Cycle consists
of the following steps – Nitrogen
fixation, Nitrification, Assimilation,
1. Atmospheric fixation: A natural
phenomenon where the energy of
lightning breaks the nitrogen
into nitrogen oxides, which are
2. Industrial nitrogen fixation:
It is a man-made alternative
that aids in nitrogen fixation
by the use of ammonia.
Ammonia is produced by the

CYCLE
organisms. Ammonification and Denitrification. then used by plants. direct combination of nitrogen
Nitrogen Cycle is a biogeochemical and hydrogen. Later, it is
converted into various
process through which nitrogen is
1. Nitrogen Fixation Process fertilisers such as urea.
converted into many forms,
consecutively passing from the 3. Biological nitrogen fixation: We already
It is the initial step of the nitrogen cycle.
atmosphere to the soil to organism Here, Atmospheric nitrogen (N2) which
know that nitrogen is not used directly
from the air by plants and animals.
and back into the atmosphere. is primarily available in an inert form, is Bacteria like Rhizobium and blue-green
converted into the usable form - algae transform the unusable form of
It involves several processes such as ammonia (NH3). nitrogen into other compounds that are
nitrogen fixation, nitrification, more readily usable. These nitrogen
During the process of Nitrogen fixation, compounds get fixed in the soil by these
denitrification, decay and the inert form of nitrogen gas is microbes.
putrefaction. deposited into soils from the atmosphere
and surface waters, mainly through
precipitation. Diazotrphs are microorganism that
Nitrogen gas exists in both organic
can convert nitrogen gas from the air
and inorganic forms. Organic nitrogen The entire process of Nitrogen fixation into a form that plants and other
exists in living organisms, and they is completed by symbiotic bacteria, which orgamisms can use, like ammonia. This
are known as Diazotrophs. Azotobacter process is called nitrogen fixation, and
get passed through the food chain by and Rhizobium also have a major role in it helps make nitrogen available in the
the consumption of other living this process. These bacteria consist of a soil, supporting plant growth. Common
organisms. nitrogenase enzyme, which has to the examples include bacteria like
capability to combine gaseous nitrogen Rhizobium (which forms nodules on
with hydrogen to form ammonia. the roots of legumes) and
Inorganic forms of nitrogen are Azotobacter.
found in abundance in the Nitrogen fixation can occur either by
atmospheric fixation- which involves Azotobacter fixes nitrogen from the
atmosphere. This nitrogen is made lightening, or industrial fixation by air into the soil using a specialized
available to plants by symbiotic manufacturing ammonia under high enzyme called nitrogenase. This
bacteria which can convert the inert temperature and pressure conditions. enzyme allows it to convert nitrogen
This can also be fixed through man- gas (N₂) from the atmosphere into
nitrogen into a usable form – such as made processes, primarily industrial ammonia (NH₃), a form of nitrogen
nitrites and nitrates. processes that create ammonia and that plants and other organisms can
nitrogen-rich fertilisers. use.
Nitrogen undergoes various types of Nitrogenase Enzyme:
transformation to maintain a balance Azotobacter produces nitrogenase,
in the ecosystem. Furthermore, this which is the key to breaking the
process extends to various biomes, strong triple bond of nitrogen gas
(N₂).
with the marine nitrogen cycle being Certain bacteria can break the
one of the most complicated nitrogen triple bond, converting N2 The nitrogenase enzyme converts N₂
into ammonia (NH3) or ammonium into ammonia (NH₃) through a series
biogeochemical cycles. (NH4+) of chemical reactions.
 2. Nitrification Importance of Nitrogen Cycle
In this process, the ammonia is
Nitrosomonas is a genus of bacteria
converted into nitrate by the 1. Helps plants to synthesise chlorophyll from the nitrogen
that converts ammonia into nitrites compounds.
presence of bacteria in the soil.
and plays a key role in the nitrogen 2. Helps in converting inert nitrogen gas into a usable
Nitrites are formed by the oxidation
cycle. form for the plants through the biochemical process.
of ammonia with the help of
3. In the process of ammonification, the bacteria help in
Nitrosomonas bacteria species. Later, Nitrobacter is a genus of bacteria that
decomposing the animal and plant matter, which
the produced nitrites are converted converts nitrite to nitrate, which is an indirectly helps to clean up the environment.
into nitrates by Nitrobacter. This important step in the nitrogen cycle. 4. Nitrates and nitrites are released into the soil, which
conversion is very important as helps in enriching the soil with the necessary nutrients
ammonia gas is toxic for plants. required for cultivation.
5. Nitrogen is an integral component of the cell and it
The reaction involved in the process of 4. Ammonification forms many crucial compounds and important
Nitrification is as follows: biomolecules.
When plants or animals die, the nitrogen
present in the organic matter is released
Nitrogen is also cycled by human activities such as the
back into the soil. The decomposers,
combustion of fuels and the use of nitrogen fertilisers.
namely bacteria or fungi present in the
These processes increase the levels of nitrogen-containing
soil, convert the organic matter back into
compounds in the atmosphere. The fertilisers containing
ammonium. This process of decomposition
nitrogen are washed away in lakes, rivers and result in
produces ammonia, which is further used
eutrophication.
3. Assimilation for other biological processes.

Conclusion
Primary producers – plants take in the
nitrogen compounds from the soil with Nitrogen is abundant in the atmosphere, but it is unusable to plants or
the help of their roots, which are 5. Denitrification animals unless it is converted into nitrogen compounds.
available in the form of ammonia, nitrite Nitrogen-fixing bacteria play a crucial role in fixing atmospheric nitrogen
ions, nitrate ions or ammonium ions and Clostridium is a genus of bacteria into nitrogen compounds that can be used by plants.
Denitrification is the process in which the
are used in the formation of the plant that are gram-positive, spore- The plants absorb the usable nitrogen compounds from the soil through
nitrogen compounds make their way back into their roots. Then, these nitrogen compounds are used for the production of
forming, and anaerobic, meaning
and animal proteins. This way, it enters the atmosphere by converting nitrate (NO3-) proteins and other compounds in the plant cell.
they don't require oxygen to live.
the food web when the primary into gaseous nitrogen (N). This process of the Animals assimilate nitrogen by consuming these plants or other animals that
consumers eat the plants. nitrogen cycle is the final stage and occurs in Pseudomonas is a group of contain nitrogen. Humans consume proteins from these plants and animals.
the absence of oxygen. Denitrification is bacteria that are commonly The nitrogen then assimilates into our body system.
carried out by the denitrifying bacterial
found in soil and water, and can During the final stages of the nitrogen cycle, bacteria and fungi help
species- Clostridium and Pseudomonas, which decompose organic matter, where the nitrogenous compounds get dissolved
cause infections in humans,
will process nitrate to gain oxygen and gives into the soil which is again used by the plants.
animals, and plants
out free nitrogen gas as a by product. Some bacteria then convert these nitrogenous compounds in the soil and
turn it into nitrogen gas. Eventually, it goes back to the atmosphere.
These sets of processes repeat continuously and thus maintain the
percentage of nitrogen in the atmosphere.
 Blue Carbon
Blue carbon is the term for carbon
captured by the world's ocean and
CARBON Carbon storage and exchange
Carbon moves from one storage reservoir to another
through a variety of mechanisms. For example, in the food
coastal ecosystems. Sea grasses, chain, plants move carbon from the atmosphere into the

CYCLE
mangroves, salt marshes, and other biosphere through photosynthesis. They use energy from the
systems along our coast are very sun to chemically combine carbon dioxide with hydrogen and
efficient in storing CO2. These areas oxygen from water to create sugar molecules. Animals that
also absorb and store carbon at a eat plants digest the sugar molecules to get energy for their
much faster rate than other areas, bodies. Respiration, excretion, and decomposition release the
such as forests, and can continue to carbon back into the atmosphere or soil, continuing the cycle.
do so for millions of years. The
carbon found in coastal soil is often The ocean plays a critical role in carbon storage, as it holds
thousands of years old. When these about 50 times more carbon than the atmosphere. Two-way
systems are damaged or disrupted by carbon exchange can occur quickly between the ocean’s
human activity, an enormous amount surface waters and the atmosphere, but carbon may be
of carbon is emitted back into the stored for centuries at the deepest ocean depths.
atmosphere, contributing to climate
change.
Rocks like limestone and fossil fuels like coal and oil are
Carbon is the foundation of all life on storage reservoirs that contain carbon from plants and
Earth, required to form complex animals that lived millions of years ago. When these
molecules like proteins and DNA. This organisms died, slow geologic processes trapped their carbon
element is also found in our and transformed it into these natural resources. Processes
atmosphere in the form of carbon such as erosion release this carbon back into the atmosphere
dioxide (CO2). Carbon helps to very slowly, while volcanic activity can release it very quickly.
regulate the Earth’s temperature, Burning fossil fuels in cars or power plants is another way
makes all life possible, is a key this carbon can be released into the atmospheric reservoir
ingredient in the food that sustains us, quickly.
and provides a major source of the
energy to fuel our global economy.

The carbon cycle describes the process

in which carbon atoms continually
travel from the atmosphere to the
Earth and then back into the
atmosphere. Since our planet and its On Earth, most carbon is stored in Carbon is released back into the In the case of the ocean, carbon is
atmosphere form a closed environment, rocks and sediments, while the rest is atmosphere when organisms die, continually exchanged between the
the amount of carbon in this system located in the ocean, atmosphere, and volcanoes erupt, fires blaze, fossil ocean’s surface waters and the
does not change. Where the carbon is in living organisms. These are the fuels are burned, and through a atmosphere, or is stored for long
located — in the atmosphere or on reservoirs, or sinks, through which variety of other mechanisms. periods of time in the ocean depths.
Earth — is constantly in flux. carbon cycles.
 Fast carbon cycle
Slow carbon cycle
The fast carbon cycle moves carbon quickly between the
atmosphere, plants, animals, and the ocean.
The slow carbon cycle is how carbon moves through the Earth over
millions of years. 1. Plants take in carbon: Plants absorb carbon dioxide (CO₂) from
the air during photosynthesis to make food.
1. Carbon leaves the air: Carbon dioxide (CO₂) in the atmosphere
mixes with rainwater, creating acid that breaks down rocks. The
Changes to the carbon cycle broken pieces wash into rivers and oceans. 2. Animals return carbon: Animals eat plants and release CO₂ back
into the air through breathing (respiration).

Human activities have a tremendous impact on the 2. Stored in the ocean: Sea creatures use the carbon to make shells.
carbon cycle. Burning fossil fuels, changing land use, and When they die, their shells pile up on the ocean floor and turn into 3. Carbon moves through decay: When plants and animals die,
using limestone to make concrete all transfer significant rocks like limestone. decomposers break them down, releasing CO₂ back into the air or
quantities of carbon into the atmosphere. As a result, soil.
the amount of carbon dioxide in the atmosphere is rapidly
rising; it is already greater than at any time in the last 3. Carbon goes back to the air: Over time, some of these rocks get
3.6 million years. The ocean absorbs much of the carbon pulled underground by Earth's movements. Volcanoes then release the 4. Ocean exchanges carbon: The ocean absorbs CO₂ from the air
dioxide that is released from burning fossil fuels. This carbon back into the atmosphere as CO₂. and can release it back, depending on conditions.
extra carbon dioxide is lowering the ocean’s pH, through
a process called ocean acidification. Ocean acidification
interferes with the ability of marine organisms (including
This process happens very slowly but helps control the amount of This cycle happens over days to years and keeps carbon moving
corals, Dungeness crabs, and snails) to build their shells
CO₂ in the air over millions of years. between living things, the atmosphere, and the ocean.
and skeletons.

The main difference between the slow carbon cycle and the fast Fast Carbon Cycle
carbon cycle is the timeframe and the processes involved:
Timeframe: Takes days to years.
Slow Carbon Cycle
Processes: Involves photosynthesis, respiration, decomposition, and
Timeframe: Takes millions of years. quick ocean-atmosphere CO₂ exchange.

Processes: Includes weathering of rocks, formation of carbonate Carbon Storage: Short-term storage in plants, animals, soil, and
rocks, subduction, and volcanic eruptions. the ocean surface.

Carbon Storage: Long-term storage in rocks, deep ocean sediments, Impact: Influences the current levels of CO₂ in the atmosphere.
and Earth's crust.

Impact: Regulates Earth's climate over geological time. In short, the slow cycle is like a long-term bank account for
carbon, while the fast cycle is like daily cash flow.
 WATER
It is a continuous process where water moves 1. Change from Liquid to
from the Earth's surface to the amtosphere and Gaseous Phase – Evaporation
back again. It's driven by the sun's energy and
gravity. and Transpiration

When the sun heats up the rivers and oceans,

water becomes water vapour and it rises up in
the air. This process is called evaporation. The
CYCLE The heat of the sun causes water from the
surface of water bodies such as oceans, streams,
and lakes to evaporate into water vapor in the
atmosphere. Plants also contribute to the water
first step of the water cycle.
cycle when water gets evaporated from the
aerial parts of the plant, such as leaves and
stems by the process of transpiration.
When the water vapour reaches up in the sky, it
turns into tiny droplets of water. These water
droplets along with various gases and dust 2. Change from Solid to
particles, come together to form clouds. This is
known as condensation. Gaseous Phase – Sublimation

When the cloud becomes too heavy and it cannot Due to dry winds, low humidity, and low air
hold any more water inside, it burst open to give pressure, snow present on the mountains change
out rain, hail or snow. This is known as directly into water vapor, bypassing the liquid
precipitation. phase by a process known as sublimation.

As it rains, water gets collected in oceans, lakes 3. Change from Gaseous to Liquid
and rivers. It even seeps through the soil and Phase – Condensation
becomes ground water. Thus, water cycle is a
continuous process of evaporation, condensation,
and precipitation.
The invisible water vapor formed through
evaporation, transpiration, and sublimation rises
through the atmosphere, while cool air rushes to
Plants sweat — transpiration. That is why it
take its place. This is the process of
rains more in places with more trees, like hill
condensation that allows water vapor to
stations and forests.
transform back into liquid, which is then stored
in the form of clouds.
Sometimes snow directly turns into water vapour Sometimes, a sudden drop in atmospheric
without melting into water. That's called temperature helps the water vapors to condense
sublimation. into tiny droplets of water that remain
suspended in the air. These suspended water
Evapotranspiration - Evaporation from soil and droplets get mixed with bits of dust in the air,
Precipitation that falls on and over land — some water surfaces, plus transpiration from plants. resulting in fog.
is intercepted by vegetation (Interception).

Percipitation infiltrates (infiltration) the soil

surface. Percolates (percolation) into the ground.
 4. Change from Gaseous to Liquid
and Solid Phase – Precipitation and
Deposition

Wind movements cause the water-laden clouds to

collide and fall back on the earth’s surface through
precipitation, simply known as rain. The water that
evaporated in the first stage thus returns into
different water bodies on the earth’s surface,
including the ocean, rivers, ponds, and lakes. In
regions with extremely cold climate with sub-zero
temperatures, the water vapor changes directly
into frost and snow bypassing the liquid phase,
causing snowfall in high altitudes by a process
known as the deposition.

5. Return of the water back into the underground

reserve – Runoff, Infiltration, Percolation, and
Collection

The water that falls back on the earth’s surface moves

between the layers of soil and rocks and is accumulated
as the underground water reserves known as aquifers.
This process is further assisted by earthquakes, which
help the underground water to reach the mantle of the
earth. Some amount of precipitated water flows down the
sides of mountains and hills to reach the water bodies,
which again evaporates into the atmosphere. During
volcanic eruptions, the underground water returns to the
surface of the earth, where it mixes with the surface
water bodies in order to continue the cycle.
 crust

The crust is the topmost layer of the

EARTH'S PLANETARY STRUCTURE mantle
Earth on which you stand. All the
mountains, jungles, and oceans you know
-Was discovered by Andrija
are held on this layer.
Mohorovicic, 1909
-It is the thinnest layer among the four
-Mantle is responsible for many
layers.
geological activities like the movement
of the plate tectonics, earthquake,
-This layer is 70 Km thick on the land,
volcanic activities, and mountain
and 5 Km thick at some points on the
formation.
ocean floor.
-2,900 km thick, 84% of the earth's
- abundant in silicate material
volume

-mostly made out of silicate material

(silicon and oxygen)
oceanic crust

The sima is the lower lithosphere Asthenosphere

-Sima is abundant in oceanic crust layer of the Earth's crust,
made up of rocks rich in -1,300 k thick
-Oceanic crust is basaltic and the -4.000 k thick located below
magnesium silicate
basalt is a type of (sima rock) -solid coldest the lithosphere semi-molten
minerals. It's also known
rocks malleable
as the basal crust, basal
layer, or oceanic crust. -malleable
-exhibit plasticity
Continental crust - toughest

-Sial is abundant in continental crust

Sial is a geochemical term for The asthenosphere is a layer of soft,
-It is always older than the oceanic the upper layer of the Earth's hot rock under the Earth's surface.
crust crust, which is rich in aluminum Saying it has plasticity means it can
silicate minerals. Sial is often bend, flow, and stretch like playdough
-continental crust is 3 granitic or used to refer to the continental or slime without breaking. This helps
abundant in granite (a type of Sial crust, which is made up of the Earth's plates move and shift
rock) igneous, metamorphic, and around, causing things like earthquakes
sedimentary rocks. and volcanoes.
 inner core What Makes the Inner Core Solid?
outer core
Despite the incredibly high temperature of the inner core
(around 5200°C9 C or 9,392°F), it remains solid due to
the immense pressure exerted by the weight of all the
layers above it [1]. This pressure is is so great that it
-Was discovered by Beno Gutenberg 1913 -Was discovered by Inge Lehmann 1936 forces the iron and nickel atoms to pack tightly together,
overcoming the expansive forces of heat.
-The outer core refers to the liquid layer of the Earth's core, -The Earth's inner core is a solid ball of mostly iron, located at
located between the inner core and the mantle. It is primarily the very center of our planet.
composed of iron with some lighter elements, and its high Growth of the Inner Core:
electrical conductivity allows for the generation of a magnetic -It has a radius of about 1,220 kilometers (758 miles) which is
field. about 20% of the Earth's radius or 70% of the Moon's radius The inner core is slowly growing as liquid iron from the
outer core crystallizes and solidifies. This process
-Temperature 3,000-4,000 k (outer) and 4,000-8,000k - mostly made out of silicate material (silicon and oxygen) releases heat, which contributes to the convection
(inner) currents in the outer core that generate the Earth's
-its is an oblate spheriod in shape and is more spherical than magnetic field
-2,400 km thick tha planet itself

-Consist mainly of Iron and Nickel Inner Inner Core:

-It is also the only layer that is completely liquid Recent discoveries suggest the inner core itself has a
core, known as the "inner inner core" This region has
distinct properties from the rest of the inner core,
including a different crystal structure and orientation

Importance of the Inner Core:

The inner core plays a crucial role in -Earth's Magnetic

Field: The inner core influences the Earthis magnetic field,
which protects us from harmful solar radiation -Earth's
Rotation: The inner core's rotation affects the Earth's
overall rotation. -Geothermal Activity. The inner core
contributes to the Earth's internal heat and drives
geological processes
 PROPERTIES OF MINERALS
What is a mineral?
DENSITY
A mineral is a naturally occurring
inorganic element or compound having This refers to the amount of matter in an
an orderly internal structure and object, or mass per unit volume expressed
characteristic chemical composition, as grams per cubic cm (g/cm³). The formula
crystal form, and physical properties. STREAK for density is p = m/v, where 'p' is density,
'm' is mass in grams, and 'v' is volume in cm
PHYSICAL PROPERTIES The color of the powder scraped off a
mineral when it is rubbed against a Every mineral has a property called density
Different properties of minerals COLOR hard, rough surface. Density is the amount of matter in a given
space Density can also be expressed as
The color of a mineral is an easily observed physical Streak can be observed by rubbing the mass per unit volume.
PHYSICAL PROPERTIES property because it appears to the naked eye. But mineral sample across a piece of
color can be used to identify only those few unglazed porcelain, which is called a
minerals that always have their own characteristic streak plate. CRYSTAL SHAPE
A physical property is a
characteristic of a substance that color.
can be observed or measured Crystal shape also known as Habit. Crystal
without changing the identity of Color is not always a reliable way to identify shape refers to the external shape of a
the substance. minerals for another reason. The colors of minerals mineral's crystals. Some minerals have
can change as a result of exposure to or treatment distinctive crystal forms that can aid in
with heat, cold, pollution, or radiation. their identification.
LUSTER
Crystal structure is the atomic
It refers to the way light is reflected from a arrangement of the mineral. The shape a
mineral surface. Luster can be of three types: HARDNESS mineral naturally forms depends on its
crystal structure.
a. Metallic luster - minerals reflect light the This refers to the measure of
way highly polished metal does. Such minerals resistance of a mineral to abrasion or
include silver, copper, gold, pyrite, and graphite. scratching. Hardness is obtained by
rubbing a mineral of unknown hardness CLEAVAGE AND FRACTURE
b. Submetallic luster - exhibited by minerals to a mineral of known hardness. • Mohs
with a dull coating tarnish and not as shiny as hardness, rough measure of the
those with metallic luster resistance of a smooth surface to Cleavage This refers to the tendency of a
scratching or abrasion, expressed in mineral to break or cleave along planes of
c. Nonmetallic luster - minerals that do not terms of a scale devised (1812) by the weak bonding. A plane of weak bonding
relwct much light Nonmetallic lusters may be German mineralogist Friedrich Mohs. occurs because some atomic bonds in a
described by a number of different terms: mineral are weaker than others. Not all
brilliant, glassy, pearly, silky, and dull, to name a minerals have cleavage.
few.
Fracture This refers to the 'breaking' of
minerals that do not have cleavage
Fracture occurs because there are minerals
having chemical bonds that are equally and
nearly equally strong in all directions.
 PROPERTIES OF MINERALS
Different properties of minerals
REACTIVITY
Special properties
Reactivity in minerals refers to
Special properties are unique and how readily a mineral reacts with
identifiable characteristics used to other substances, particularly
identify minerals or that allow acids and water.
some minerals to be used for Sulfur smells like
special purposes. rotten egg
SMELL
Flourescence
Is the ability of certain minerals to The smell of minerals is a distinctive
emit visible light when exposed to characteristic that can help identify
ultraviolet (UV) radiation. them. It's caused by the release of
volatile compounds when the mineral is
MAGNETIte broken, scratched, or exposed to air or
MAGNETISM water.

Magnetism in minerals refers to Halite also known as

the ability of certain minerals to TASTE
be attracted or repelled by a
rock salt, salty taste
magnetic field. This property The taste of a mineral is determined by
arises from the alignment of the interaction of its ions with the
electrons within the mineral's taste buds on our tongue. Different
atomic structure. minerals have different ionic
compositions, which result in unique
taste sensations.
RADIOACTIVITY
Autunite Minerals are radioactive if they contain
radioisotopes, and the amount of
radioactivity depends on isotope
concentration. Most minerals that contain
potassium, uranium, and thorium are
radioactive, but many other elements
besides these three can also contribute to
radioactivity.