Biochemical cycles

A biochemical cycle refers to the natural cycle of the earth through which a chemical substance or matter moves through the biotic and abiotic components of the earth. These components always interact with each other and form a stable system in the biosphere.
There are four main biogeochemical cycles

•    The Water Cycle
•    The Nitrogen Cycle
•    The Carbon Cycle
•    The Oxygen Cycle
WATER CYCLE:

 

 

 

 

 

 

 

 

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.
The water cycle in nature is also known as hydrological cycle. The various steps involved in the water cycle in the biosphere are:
1. Evaporation:
Evaporation is when the sun heats up water in seas and oceans and turns it into water vapour or steam.

•    The Sun’s heat provides energy to evaporate water from the Earth’s surface (oceans, lakes, etc.) and form water vapour which being lighter than air rises up and goes into the atmosphere.

2. Transpiration -The plants continuously absorb water from the soil through their roots.

•    Some of this water is utilized by the plants for photosynthesis.
•    The excess water in the body of plants is added to the atmosphere in the form of water vapour from the leaves of plants through the process of transpiration.
•    The water vapours produced also goes into the atmosphere.
•    Transpiration is the process by which plants and trees lose water out of their leaves into the air.
3. During the process of respiration in living plants and during the decay of dead plants water vapour is produced which also goes into the atmosphere.

4. Condensation– As the water vapour rises up, it gets cooled and it eventually condenses back into tiny droplets of liquid water.

5. These droplets are small enough to float in the air and eventually collect together to make a cloud. These clouds can be blown by the wind to move water to different parts of the earth.

6. Precipitation-As more and more water droplets form, they will join together to form bigger water drops in the clouds.

•    These drops become too heavy to stay in the air and will fall to the earth as rain.
•    In case of extremely cold weather, the water might freeze and fall as hail or snow.
•    Any water that falls from the sky-rain, snow, sleet or hail is called precipitation.
7. Percolation and absorption: Some of the precipitation soaks into the ground.

•    Some of the underground water percolates through the rock or clay layers to reach the underground water.
•    This is called groundwater.
•    On land the water is used by the plants, crops and trees to grow. But most of the water flows downhill as runoff (above ground or underground), eventually returning to the seas as slightly salty water.
•    In this way water was taken from the earth, returns to the earth and the water cycle is completed.
NITROGEN CYCLE:

 

 

 

 

 

 

 

 

•    Nitrogen makes up seventy-eight percent of the atmosphere, but most organisms cannot use this form of nitrogen, and must have the fixed form.
•    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.
•    The nitrogen cycle produces the fixed form of nitrogen these organisms need.
Step 1-

Nitrogen Fixation

By lightning– 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.

By bacteria– Molecular nitrogen is converted into nitrates and nitrites by free living bacteria or the bacteria like Rhizobium present in the root nodules of legumes.

•    Special bacteria convert the nitrogen gas (N2) to ammonia (NH3) which the plants can use.

Step 2-

Nitrification– Nitrification is the process which converts the ammonia into nitrite ions and then into nitrates which the plants can take in as nutrients.

•    Special kinds of bacteria are involved in this process which occurs naturally in the environment.
•    The bacteria nitrosomonas and nitrococcus convert the ammonia into nitrite and then nitrobacter convert the nitrites into nitrates by oxidizing NO2 to NO3.
•    All these bacteria reside in soil and are called as nitrifying bacteria.
•    These soluble nitrates dissolve in soil water and are absorbed by the roots of plants.
•    The nitrates and nitrites are used by plants to make amino acids which are then used to make plant proteins.
•    The plant may be eaten by an animal, and its biomass used to produce animal protein.

Step 3-

Ammonification– When an animal or plant dies they release wastes from their bodies, nitrogen is released in the organic form.

•    This organic nitrogen is converted into ammonium by fungi and bacteria through the process Ammonification.
•    After all of the living organisms have used the nitrogen, decomposer bacteria convert the nitrogen-rich waste compounds into simpler ones.
•    Urea and egested material is broken down by decomposers.
•    This results in nitrogen being returned to the soil as ammonia.
•    Decomposers also break down the bodies of dead organisms resulting in nitrogen being returned to the soil as ammonia.

Step 4-

Denitrification- Denitrification is the final step in which the simple nitrogen compounds are converted back into nitrogen gas (N2), which is then released back into the atmosphere to begin the cycle again.

•    When the ammonia is converted back into inert nitrogen, the process is called as denitrification.
•    Bacteria are involved in this process which takes place in anaerobic conditions.
•    Places like deep soils and deep water are the places without oxygen.
•    Pseudomonas and Clostridium are responsible for the step of denitrification.
•    These bacteria can also live in the places where there is availability of oxygen.

CARBON CYCLE:


 

 

 

 

 

•    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 hydrogen carbonate salts in various minerals, while all life-forms are based on carbon-containing molecules like proteins, carbohydrates, fats, nitrogen-cycle in nature nucleic acids and vitamins.
•    The endoskeletons and exoskeletons of various animals are also formed from carbonate salts.

The carbon cycle is the process by which carbon moves from the atmosphere into the Earth and its organisms and then back again.
Carbon enters the atmosphere as carbon dioxide from respiration (breathing) and combustion (burning)
Photosynthesis

•    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.
•    Plants store and use this sugar to grow and to reproduce.
•    Thus, plants help to remove carbon from the atmosphere.
•    When plants are eaten by animals, their carbon is passed on to those animals.
•    Since animals cannot make their own food, they must get their carbon either directly by eating plants or indirectly by eating animals that have eaten plants.
At the same time that some processes of nature are removing carbon from the air, other processes are adding more carbon to the air.
Respiration: Respiration is the next step in the cycle, and it occurs in plants, animals, and even decomposers.
•    When plants and animals respire, glucose stored in the plants and animals are broken down to release CO2, water and energy.
•    Through this process, CO2 is released back into the atmosphere.
Decomposition: As plants and animals die and decay or decompose (or when animals defecate and their waste materials decompose), the carbon found in them are released to the environment.

•    When the decaying matter bodies get buried under the ground and are subjected to high pressures and other physical and chemical changes for millions of years, they change into fossil fuels.

Combustion: When the fossil fuels are burnt to provide energy for various needs like heating, cooking, transportation and industrial processes most of the carbon rapidly enters the atmosphere as carbon dioxide gas.

•    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.

Movement of carbon from the atmosphere to the oceans: The oceans, and other water bodies, soak up about a quarter of the carbon dioxide gas from the atmosphere.

 

 

•    However, this uptake process is slow.
•    Similarly, under normal conditions, the release of carbon dioxide back into the atmosphere from the ocean is also at a very low rate.
Through these steps the total amount of carbon in the environment remains constant. There is no formation or demolition of carbon in this process and it only involves the movement of this element from one form to another.

OXYGEN CYCLE:

•    Oxygen is an important element to life on Earth.
•    It is the most common element of the human body.
•    It makes up about 65% of the mass of the human body.
•    Most of this is in the form of water (H2O).
•    Oxygen also makes up about 30% of the Earth and 20% of the atmosphere.

The Oxygen Cycle

Oxygen is constantly being used and created by different processes on planet Earth. All of these processes together make up the oxygen cycle. The oxygen cycle is interconnected with the carbon cycle.

Processes That Use Oxygen

  • Respiration:

Animals take in simple sugars (glucose) and oxygen and release carbon dioxide, water and energy.

•    Decomposition: Is a minor part of the Carbon/Oxygen cycle
Decomposition is when any organic matter (plants, animals) breaks down chemically into all the simple elements that they are made of and these elements return back to the environment.

As plants and animals die and decay or decompose (or when animals defecate and their waste materials decompose), the carbon, oxygen, nitrogen, water, calcium etc. return to the soil and air during decomposition.

Processes That Produce Oxygen

  • Photosynthesis:

Green plants/trees take in Carbon Dioxide and water using the chlorophyll in their leaves and energy from the sun they release Oxygen, sugar and water vapor.

•    Sunlight – Some oxygen is produced when sunlight reacts with water vapor in the atmosphere.