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OXYGEN CYCLE : EASY WAY TO EXPLAIN BIOGEOCHEMICAL CYCLE

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OXYGEN CYCLE

INTRODUCTION

It is a type of cyclic flow of nutrients between non- living components like soil, rock air and water and living organisms. It makes the biosphere dynamic. In oxygen cycle there is a cyclic flow of atmospheric oxygen. Photosynthesis releases oxygen in the atmosphere.  Respiration absorbs oxygen. By photosynthesis plant  produces organic molecules (C6 H12 O6). By respiration that organic molecule is oxidized to release energy and carbon oxide.

IMPORTANT POINTS IN OXYGEN CYCLE

 In atmosphere, oxygen cycle maintains the proper level of oxygen with required proportion.Oxygen cycle maintains the level of oxygen in the atmosphere. The living organisms use up important gases as oxygen from the atmosphere by combustion or burning,  cellular respiration and in the formation of oxides of nitrogen.

Photosynthesis is the only major process green plants . In this way oxygen returns to the atmosphere. So we can say green plants are the major source of oxygen in the atmosphere.

Beside oxygen cycle there are some other biogeochemical cycle like Nitrogen cycle, carbon cycle and ozone layer.

NITROGEN CYCLE WITH OXYGEN CYCLE

Nitrogen is  an important  nutrient for all life- forms.  Nitrogen is present as element in the atmosphere , then it  passes from its elemental form into simple nitrogenous compounds present in the soil  in nitrogen cycle in oxygen cycle and water. It enters the living beings and forms complex molecules in them as nucleic acid, protein molecule etc. These complex molecules are then broken down again to release nitrogen back into atmosphere.

Nitrogen cycle involves following important steps like:

  • NITROGEN FIXATION:  nitrogen fixing bacteria like Rhizobium  converts inert nitrogen into  nitrates or nitrite. These bacteria in nitrogen cycle in oxygen cycle leave in the roots of leguminous plants. By lightning also this conversion occurs.
  •   NITROGEN ASSIMILATION: Plants absorb nitrates and nitrites and convert them to amino acids. Amino acid is the main component of protein. Animals can intake this protein  in nitrogen cycle in oxygen cycle directly or indirectly.
  • AMMONOFICATION : It is the process of production of ammonia in nitrogen cycle in oxygen cycle. It occurs by the decomposition  of dead plants and animals.
  • NITRIFICATION:  Here ammonia converts into nitrites, then to nitrates. Nitrifying bacteria like Nitrosomonas  and Nitrobacter . The following reaction is NH4+ ————à NO2 ———–à NO3 . NH4 ion to NO2  ion conversion done by Nitrosomonas bacteria. NO2  ion to NO3 ion change is done by Nitrobacter.
  • DENITRRIFICATION: It is the process of reducing nitrates or ammonia, present in the soil to molecular nitrogen (N2). It goes back into the atmosphere. Pseudomonas  bacteria does this process.

THE CARBON CYCLE WITH OXYGENCYCLE

We find carbon in various forms on the earth. It occurs in the elemental form as diamond and graphite. In combined state we find carbon as

  • In the atmosphere as carbon di oxide.
  • Various minerals contain carbonate and hydrogen carbonate salts.
  • Fossil fuels like coal, petroleum and natural gas.
  • Carbon containing molecules like proteins, fats, nucleic acid, vitamins, carbohydrates.
  • Endoskeleton and exoskeleton of various animals like mollusk, fish, mammals.

Nature incorporate carbon in our life by photosynthesis through plants. During this process green plats prepare food with the help of water, sunlight and CO2.

The other processes that give out carbon di oxide into atmosphere are

  • Decomposition of dead plants and animals by decomposers.
  • Combustion of fossil fuels like coal and petroleum in large scale.
  • Weathering of rocks and volcanic eruptions.

THE OXYGEN CYCLE

Oxygen is an abundant element forming about 20.95% or 21% of the atmospheric gases. In various organic molecules like proteins, fats and carbohydrates, oxygen plays an important role as component.

In Earth’s crust it is found as oxides of many metals and also as carbonate, sulphate, nitrate  and other minerals. It is present in combined form also as in carbon di-oxide  and in water.

In oxygen cycle , oxygen level in atmosphere is properly maintained. Various physiological and physical processes like combustion, respiration and formation of oxides of nitrogen use up the atmospheric oxygen.  

Photosynthesis  is the only major process, by which oxygen is returned  to the atmosphere. That iswhy we can say the green plants as one of the important sources of oxygen.

OZONE LAYER IN OXYGEN CYCLE

Ozone is a tri atomic molecule of oxygen with the formula O3. it is found in the upper region of the atmosphere , above the region  where elemental  oxygen (diatomic molecule) is present. Ozone is poisonous and luckily, it is not stable near Earth’s surface.  

IMPORTANCE OF OZONE IN OXYGEN CYCLE

Ozone forms a thick layer like a shield in the upper region of atmosphere and absorbs ultraviolet radiations from the sun. in this way, ozone layer prevents these radiation from reaching the surface of the earth. Ozone gas protects whole living world from UV  radiation..

THREAT TO OZONE LAYER IN OXYGEN CYCLE

Various man-made materials like chlorofluorocarbons or CFCs are very stable as it is made up of fluorine and chlorine. Natural biological process cannot degrade these CFCs. So this harmful chemicals reach the ozone layer. They react with this layer. It results in the reduction  or thinning of ozone layer. For this reason there is an  OZONE HOLE above Antarctica in 1985.

QUESTION RELATED TO OXYGEN CYCLE AND OTHER BIO-GEO- CHEMICAL CYCLE

Qs1: What is the percentage of oxygen found in the atmosphere?

Ans1: 20.94% oxygen is present in atmosphere.

Qs2: Name any two compounds of oxygen found in nature.

Ans2: Diatomic compound is oxygen (O2). Triatomic compound is ozone (O3).

Qs3: Name any three processes in which oxygen is used up in atmosphere.

Ans3 : Living organism using oxygen in the following processes

  • Respiration in all living organism
  • Combustion of fossil fuel
  • Decomposition of organic matter

Qs4: Carbon di-oxide is necessary gas for plants. Why do we then consider it as a pollutant?

Ans4: Plants need carbon di oxide gas to perform photosynthesis process. But this gas is also a green house gas. Up to 350 ppm concentration in atmosphere, it is both a good raw material as well as essential for keeping the earth warm.

But, when concentration of this gas rises from its specified level, it starts acting as a pollutant and causes pollution and global warming.  It results increase of temperature of earth which leads to global warming. It also causes melting of polar ice and glaciers which causes submerging of coastal area.

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