Bio - Cycles

Unit I (USLSC504)
Asst.Prof :Yogita Walke
Department of LifeSciences
Jai Hind College,Mumbai
Theories of Succession
Stages of Succession
pH= 3.7
pH= 7.3
Biogeochemical Cycles
What Sustains Life on Earth?
Biogeochemical or Nutrient cycle
These cyclic movements of chemical elements
of the biosphere between the organisms and
environment are referred as biogeochemical
or nutrient cycle
(Bio = living, geo = rock, chemical = element).
 Nutrient
Cycles: Global Recycling
Global Cycles recycle nutrients through the
earth’s air, land, water, and living organisms.
Nutrients are the elements and compounds that
organisms need to live, grow, and reproduce.
Biogeochemical cycles move these substances
through air, water, soil, rock and living organisms.
Types of a biogeochemical cycle
1. Gaseous cycle: the reservoir for gaseous type of nutrient
cycle (e.g., nitrogen, carbon cycle) exists in the
atmosphere. Gaseous cycles include those of Carbon,
Nitrogen, Oxygen and Water.
2. Sedimentary cycle: the sedimentary cycle (e.g., sulphur
and phosphorus cycle), the reservoir is located in Earth’s
crust. Sedimentary cycles include those of iron, calcium,
phosphorus, and other more earth bound elements
Components of a biogeochemical cycle
1. Reservoir pool - atmosphere or rock, which stores large
amounts of nutrients.The function of the reservoir is to
meet with the deficit which occurs due to imbalance in
the rate of influx and efflux
2. Cycling pool or compartments of cycle- which are the
decomposers), soil, water and air in which Nutrients
stays temporarily.
Nitrogen cycle
Nitrogen is an essential component of protein and required
by all living organisms including human beings.
Our atmosphere contains nearly 78% of nitrogen but it
can not be used directly by the majority of living
Broadly like corbondioxide, nitrogen also cycles from
gaseous phase to solid phase then back to gaseous phase
through the activity of a wide variety of organisms.
Cycling of nitrogen is vitally important for all living
There are five main processes which are essential for
nitrogen cycle
(a) Nitrogen fixation:(Conversion of N2 → NH3 )This
process involves conversion of gaseous nitrogen into
Ammonia, a form in which it can be used by plants.
Atmospheric nitrogen can be fixed by the following three
(i) Atmospheric fixation: Lightening, combustion and
volcanic activity help in the fixation of nitrogen.
(ii) Industrial fixation: At high temperature (400oC) and high
pressure (200 atm.), molecular nitrogen is broken into atomic
nitrogen which then combines with hydrogen to form
2 NO2 + O ----------> N2O5
(iii) Bacterial fixation: There are two types of bacteria:
• Symbiotic bacteria e.g. Rhizobium in the root nodules of
leguminous plants.
• Free living or assymbiotic e.g. 1. Nostoc 2. Azobacter 3.
Cyanobacteria can combine atmospheric or dissolved
nitrogen with hydrogen to form ammonia.
(c) Assimilation: (Roots absorb NH3, NH4, or NO3 and
incorporate them into nucleic acids and protein )In this
process nitrogen fixed by plants is converted into organic
molecules such as proteins, DNA, RNA etc. These molecules
make the plant and animal tissue.
(d) Ammonification : (Amino acids and nucleotides are
broken down into waste products NH3 or NH4 )Living
organisms produce nitrogenous waste products such as urea
and uric acid. These waste products as well as dead remains
of organisms are converted back into inorganic ammonia by
the bacteria. This process is called
Actinomycetes and Bacilli
(b) Nitrification: (Conversion of NH3 →NO3 )It is a
process by which ammonia is converted into nitrites by
Nitrococcus and Nitrosomonas bacteria. Another soil
bacteria Nitrobacter can covert nitrite into nitrate NO3.
In the first step, bacteria such as Nitrosomonas convert the
ammonia (or ammonium ions) to nitrites NO2.
Nitrites are very toxic to plants, so a second conversion is
necessary. This is accomplished by bacteria, such as
Nitrobacter, that convert the nitrites to nitrates NO3 .
Since flowering plants use nitrates more readily than
ammonia as a nitrogen source, nitrification is important to the
maintenance of the earth’s flora.
(e) Denitrification: (The reduction of NO3 to N2 )
Conversion of nitrates back into gaseous nitrogen is
called denitrification. Denitrifying bacteria live deep in
soil near the water table as they like to live in oxygen
free medium. Denitrification is reverse of nitrogen Pseudomonas
2 NO3 ----------> 2 NO2 ----------------> 2 NO ----------->N2
F) Sedimentation
Nitrogen Fixation
Carbon cycle
The atmosphere only contains about 0.04 per cent of total
global carbon.
Total quantity of global carbon found dissolved in oceans is
71 per cent. This oceanic reservoir regulates the amount of
carbon dioxide in the atmosphere.
Carbon constitutes 49 percent of dry weight of organisms
Fossil fuel also represent a reservoir of carbon. Carbon
cycling occurs through atmosphere, ocean and through living
and dead organisms. According to one estimate 4 × 1013 kg
of carbon is fixed in the biosphere through photosynthesis
annually. A considerable amount of carbon returns to the
atmosphere as CO2 through respiratory activities of the
producers and consumers.
Decomposers also contribute substantially to CO2 pool by
their processing of waste materials and dead organic matter of
land or oceans. Some amount of the fixed carbon is lost to
sediments and removed from circulation.
Burning of wood, forest fire and combustion of organic
matter, fossil fuel, volcanic activity are additional sources for
releasing CO2 in the atmosphere.
Human activities have significantly influenced the carbon
cycle. Rapid deforestation and massive burning of fossil fuel
for energy and transport have significantly increased the rate
of release of carbon dioxide into the atmosphere and caused
global warming.
The global carbon cycle consists of following steps1. Photosynthesis
2. Respiration
3. Decomposition
4. Combustion
5. Impact of human activities
Water Cycle or Hydrologic Cycle
Water is essential for life. No organism can survive without
water. Precipitation (rain, snow, slush dew etc.) is the only
source of water on the earth. Water received from the
atmosphere on the earth returns back to the atmosphere as
water vapour resulting from direct evaporation and through
evapotranspiration the continuous movement of water in the
biosphere is called water cycle (hydrological cycle). Earth is
a watery planet of the solar system, about 2/3rd of earth
surface is covered with water. However a very small fraction
of this is available to animals and plants. Water is not evenly
distributed throughout the surface of the earth. Almost 95 %
of the total water on the earth is chemically bound to rocks
and does not cycle.
Out of the remaining 5%, nearly 97.3% is in the oceans and
2.1% exists as polar ice caps. Thus only 0.6% is present as
fresh water in the form of atmospheric water vapours,
ground and soil water.
The driving forces for water cycle are 1) solar radiation 2)
gravity . Evaporation and precipitation are two main
processes involved in water cycle. These two processes
alternate with each other Water from oceans, lakes, ponds,
rivers and streams evaporates by sun’s heat energy. Plants
also transpire huge amounts of water. Water remains in the
vapour state in air and forms clouds which drift with wind.
Clouds meet with the cold air in the mountainous regions
above the forests and condense to form rain precipitate which
comes down due to gravity.
Sulphur cycle
Sulphur has its reservoir both in atmosphere (as oxides of
sulphur, hydrogen sulphide) and in rocks and sediments (as
mineral pyrites).
Atmospheric sulphur plays an important role, as the oxides of
sulphur react with rain water producing sulphuric acid, which
comes down as ‘acid rain’.
Oxides of sulphur (SOx) are released into the atmosphere due
to burning of fossil fuels. Thus human beings play a
significant role in the material cycling of sulphur.
In the soil or water, there are different groups of microorganisms which carry out oxidation and reduction of various
sulphur compounds.
A special role is played by Thiobacillus bacterium, which
converts sulphides into sulphuric acid. These bacteria help in
bio-leaching of metals from ores containing pyrites (S) as
Effects of Human Activities
on the Sulfur Cycle
 We
add sulfur dioxide to the atmosphere by:
– Burning coal and oil
– Refining sulfur containing petroleum.
– Convert sulfur-containing metallic ores into free
metals such as copper, lead, and zinc releasing
sulfur dioxide into the environment.
Phosphorous cycle
Phosphorus is a major constituent of biological membranes,
nucleic acids and cellular energy transfer systems. Many
animals also need large quantities of this element to make
shells, bones and teeth. The natural reservoir of
phosphorus is rock, which contains phosphorus in the form
of phosphates PO43- . When rocks are weathered, minute
amounts of these phosphates dissolve in soil solution and are
absorbed by the roots of the plants and incorporated into
nucleic acids, phospholipids and ATP . Herbivores and other
animals obtain this element from plants. PO43- is released to
the soil again by decomposers. Dissolved PO43- gets
absorbed by algae and aquatic plants.
The waste products and the dead organisms are decomposed
phosphorus.Decomposers break down waste and returns
PO43- to sediments on the seabed.
uptake by
uptake by weathering
leaching, runoff
in Soil Water,
in Ocean
Lakes, Rivers
settling out
uplifting over
geologic time
Marine Sediments
Effects of Human Activities
on the Phosphorous Cycle
 We
remove large amounts of phosphate from
the earth to make fertilizer.
 We reduce phosphorous in tropical soils by
clearing forests.
 We add excess phosphates to aquatic
systems from runoff of animal wastes and