Biogeochemical
Cycles
The sum of Earth’s ecosystems makes a biosphere.
• Biogeochemical Cycles
are cyclic paths of elements
and inorganic compounds
that sustain life, referred to
as nutrients, from the
atmosphere to the
lithosphere (soil) or
hydrosphere (water) into
living things and then back
into these environments.
The sum of Earth’s ecosystems makes a biosphere.
Also known as Material
Cycle.
Biogeochemical Cycles
1. Carbon Cycle
• The Carbon Cycle includes the processes and
pathways involved in capturing inorganic
carbon- containing molecules, converting them
into organic molecules that are used by
organisms, and the ultimate release of
inorganic carbon molecule back to the abiotic
environment. During photosynthesis, green
plants absorb carbon dioxide from the air and
combine it with hydrogen from water absorbed
from the soil. Complex organic molecules such
as sugar or carbohydrates are formed and
oxygen molecules are released into the
atmosphere. Consumers use these organic
molecules as food.
• Consumers use these organic
molecules as food. Animal cells burn
sugars in the process known as
respiration, releasing carbon dioxide
back to the atmosphere. Decomposers,
on the other hand, use the organic
molecules contained in animal waste
products and dead organisms as food.
1. Carbon Cycle The decay process releases carbon
dioxide and water back into the
environment. Buried plant and animal
materials become fossil fuels (coal, oil,
and natural gas) by geologic forces.
When we burn fossil fuels, the carbon
reenters the active carbon cycle.
The hydrologic cycle, or water cycle,
collects, purifies and distributes the Earth’s
fixed water supply. The main processes in
this water recycling and purifying cycle are:
1. Evaporation – conversion of water to
vapor
2. Condensation – conversion of water
2. Hydrologic vapor to droplets of liquid water
3. Transpiration – the process in which
Cycle water, after being absorbed by the root
system of plants and passing through
their living structure, evaporates into the
atmosphere as water vapor
4. Precipitation, such as dew, rain, sleet,
hail, snow; and runoff, which is the
draining of water back to the sea to
begin the cycle again.
3.
• Nitrogen Cycle involves the cycling of
nitrogen atoms between the abiotic and
biotic components and among the
organisms in an ecosystem. The
Nitrogen
nitrogen gas present in the atmosphere
(constitutes about 79%) is not
absorbable by most organisms. The
cycle is heavily dependent on
Cycle
microorganisms that can convert
atmospheric nitrogen into absorbable
forms.
3. Nitrogen Cycle
Ammonifying bacteria
convert nitrogen-containing Nitrogen-fixing bacteria
Nitrifying bacteria convert
wastes and bodies of dead (e.g. Rhizobium) convert
ammonia to nitrite (NO2)
plants and animals into atmospheric nitrogen (N2)
and then to nitrate (NO3).
ammonia (NH3) and to ammonia.
ammonia salts.
Denitrifying bacteria
convert nitrate to nitrogen Anammox bacteria oxidize
gas, thus removing ammonia by using nitrite as
bioavailable nitrogen and the electron acceptor to
returning it to the produce gaseous nitrogen.
atmosphere.
4. Oxygen Cycle
The oxygen cycle is a biological process which helps in
maintaining the oxygen level by moving through three main
spheres of the earth which are:
• Atmosphere
• Lithosphere
• Hydrosphere
4. Oxygen Cycle
• This biogeochemical cycle explains the
movement of oxygen gas within the
atmosphere, the ecosystem, biosphere
and the lithosphere. The oxygen cycle is
interconnected with the carbon cycle.
• The atmosphere is the layer of gases
presents above the earth’s surface.
Lithosphere is the solid outer section
along with the earth’s crust and it is the
largest reservoir of oxygen.
Stages of the Oxygen Cycle
• Stage-1: All green plants during the
process of photosynthesis, release
oxygen back into the atmosphere as a
by-product.
4. Oxygen • Stage-2: All aerobic organisms use free
Cycle oxygen for respiration.
• Stage-3: Animals exhale Carbon dioxide
back into the atmosphere which is again
used by the plants during
photosynthesis. Now oxygen is balanced
within the atmosphere.
• Phosphorus Cycle can be short term or
long-term.
• Short term cycling of phosphorus starts
when plants get phosphorus from the
5. Phosphorus Cycle soil. Consumers obtain phosphorus
by eating the plants.
• Decomposition of dead organic matter
from producers and consumers bring
back phosphorus to the soil for recycling.
5. Phosphorus Cycle
• Long term cycle involves leaching of phosphates into bodies
of water settling into sediments, and later on incorporated
into rocks as insoluble compounds.
• Geologic processes elevate these deposits and expose them to
erosion making them available to organisms. Phosphorus can
be released by weathering and taken up by plant roots.
6. Sulfur Cycle
•Sulphur is one of the most abundant
elements on the earth. It is a yellow, brittle,
tasteless, odourless non-metal. Sulphur is
present in all kinds of proteins.
•Plants directly absorb sulphur-containing
amino acids such as methionine, cystine,
and cysteine.
6. Sulfur Cycle
• Sulphur is released into the
atmosphere by the burning
of fossil fuels, volcanic
activities, and decomposition
of organic molecules.
• On land, sulfur is stored in
underground rocks and
minerals. It is released by
precipitation, weathering of
rocks and geothermal vents.
6. Sulfur Cycle
• The sulfur is released by
the weathering of rocks.
• Sulphur comes in contact
with air and is converted
into sulphates.
• Sulphates are taken up by
plants and microbes and
are converted into organic
forms.
6. Sulfur Cycle
• The organic form of sulfur is then
consumed by the animals through their
food and thus sulfur moves in the food
chain.
• When the animals die, some of the sulfur is
released by decomposition while some
enter the tissues of microbes.
6. Sulfur Cycle
• There are several natural sources such as
volcanic eruptions, evaporation of water, and
breakdown of organic matter in swamps, that
release sulphur directly into the atmosphere. This
sulphur falls on earth with rainfall.
