1) The term gaseous cycle refers to the transformation of gases between various biogeochemical reservoirs. 2) Important gaseous cycles are- a) Nitrogen Cycle. b) Carbon cycle. c) Water cycle. a) Nitrogen cycle- It is a process by which nitrogen is converted between its various chemical forms. This transformation can be carried out through both biological and physical processes. Steps of nitrogen cycle- 1) Nitrogen fixation 2) Nitrification 3) Assimilation 4) Ammonification 5) Denitrification. b) Carbon cycle- It is the biogeochemical cycle by which carbon is exchanged among the biosphere, geosphere, hydrosphere, and atmosphere of the earth. Steps of carbon cycle- following are the major steps involved in the process of carbon cycle i.e.- 1) Photosynthesis 2) Consumed by animals 3) Decomposition 4) Respiration 5) Combustion 6) Carbon in oceans. c) Water cycle- Also known as hydrologic cycle. It describe the continuous movement of water on, above and below the surface of earth.

1. GASEOUS CYCLE
Garima Thakur
M.Sc Zoology 1

2. Gaseous cycle
• The term gaseous cycle refers to the transformation of
gases between various biogeochemical reservoirs.
• Important gaseous cycles are-
1. Nitrogen Cycle
2. Carbon cycle
3. Water cycle
NITROGEN CYCLE
It is a process by which nitrogen is converted between its
various chemical forms. This transformation can be carried out
through both biological and physical processes.
Steps of nitrogen cycle-
1. Nitrogen fixation
2. Nitrification
3. Assimilation
4. Ammonification
5. Denitrification

3. Nitrogen
fixation
• It is the initial step of nitrogen cycle. Here atmospheric
nitrogen which is primary available in an inert form, is
converted into the usable form ammonia. The entire
process is regulated by symbiotic bacteria which are
known as diazotrophs. Rhizobium also have a major role
in this process.
• Types of nitrogen fixation-
 Atmospheric nitrogen fixation
 Biological nitrogen fixation
 Industrial nitrogen fixation
NITRIFICATION
In this process the ammonia is converted into nitrate by the
presence of bacteria in the soil. Nitrite are formed by the
oxidation of ammonia with the help of nitrosomonas
bacteria. Later the Nitrite are converted into Nitrate by
nitrobacteria.

4. Assimilation
• Plants takes in the nitrogen compounds from the soil with the
help of roots, which are available in the form of ammonia,
nitrite ions, nitrate ions or ammonium ions. This way it enters
the food web when consumer eat the plants.
AMMONIFICATION
When plants and animals die, the nitrogen present in the
organic matter is released back to the soil. The decomposers,
convert the organic matter back to ammonia.
DENITRIFICATION
It is the process in which the nitrogen compounds make its way back
into the atmosphere by converting Nitrate into gaseous Nitrogen. This
is the final stage and occurs in the absence of oxygen. It is carried out
by the denitrifying bacteria species pseudomonas.

6. CARBON CYCLE It is the biogeochemical cycle by which carbon is exchanged
among the biosphere, geosphere, hydrosphere, and
atmosphere of the earth.
Steps of carbon cycle- following are the major steps involved in
the process of carbon cycle i.e.-
 Photosynthesis
 Consumed by animals
 Decomposition
 Respiration
 Combustion
 Carbon in oceans
PHOTOSYNTHESIS Carbon moves from the atmosphere to plants. In the
atmosphere, carbon is attached to the oxygen in a gas called
carbon dioxide. Through the process of photosynthesis carbon
dioxide is pulled from the air to produce food made from
carbon for plant growth.

7. CONSUMED BY
ANIMALS
Carbon present in the plants moves to animals with the help of
food chain.
DECOMPOSITIONCarbon moves from plants and animals to soil. when the plants
and animals die. Their bodies, wood, leaves decay bringing the
carbon into the soil.
RESPIRATION
Carbon moves from living things to atmosphere. Each time we
exhale, we are releasing carbon dioxide gas into the
atmosphere.
COMBUSTION
Carbon moves from fossil fuel to the atmosphere. When
humans burns the fossil fuels by power factories, power plants,
cars, truck, most of the carbon quickly enters the atmosphere
as carbon dioxide.
CARBON IN
OCEANS
The oceans and other water bodies absorb some carbon from
the atmosphere and thus complete the cycle.

9. WATER CYCLE Also known as hydrologic cycle. It describe the continuous
movement of water on, above and below the surface of earth.
Steps of water cycle-
 Evaporation- the water cycle starts with the evaporation. It is the process in
which surface water turns into water vapors. Through this process water enters
from hydrosphere to atmosphere.
 Condensation- the water droplets come close together and form clouds and
fog.
 Precipitation- the clouds then pour down with the help of precipitation due
to wind or temp. change. This water droplets falls down as rain, and water enters
into lithosphere.
 Transpiration- it is similar to evaporation where liquid water is turned into
water vapors by the plants.
 Run off- as the water pours down it leads to run off. It is the process where
water runs over the surface of earth.
 Infiltration- some of the water that precipitate does not run off in the river
and is absorbed by plants or gets evaporates. Water moves deep into the soil.