B.Sc First Year Environmental Science Syllabus

1. Oxygen Cycle
Dr.AsmitaDaspute.
AssistantProfessor
Dept.ofEnvironmentalScience
SBESCollegeofScience,Aurangabad

2. 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
•Biosphere
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.

3. Oxygen Cy Oxygen Cycle cle
Atmospher
The atmosphere is 20.9% oxygen by volume, which equates to a total of roughly 34 × 1018 mol of oxygen.
Other oxygen containing molecules in the atmosphere include ozone (O3), carbon dioxide (CO2), water vapor
(H2O), and sulphur and nitrogen oxides (SO2, NO, N2O, etc.).
Biosphere
The biosphere is 22% oxygen by volume present mainly as a component of organic molecules (CxHxNxOx) and
water molecules
Hydrosphere
The hydrosphere is 33% oxygen by volume present mainly as a component of water molecules with dissolved
molecules including free oxygen and carbonic acids (HxCO3).
Lithosphere
The lithosphere is 46.6% oxygen by volume present mainly as silica minerals (SiO2) and other oxide minerals.

4. Biological production
The main source of atmospheric free oxygen is photosynthesis, which produces sugars and free oxygen from carbon dioxide and water:

5. Ddssssss
Stage-1:
All green plants during the process of photosynthesis, release oxygen back into the atmosphere as a by-product.
Stage-2:
All aerobic organisms use free oxygen for respiration.
Stage-3:
Animals exhale Carbon dioxide back into the atmosphere which is again used by the plants during photosynthesis.

7. Biological Importance of Oxygen
• Humans need it to breathe • Needed for decomposition of organic waste
• Water can dissolve oxygen and it is this dissolved oxygen that supports aquatic life.

8. Ecological Importance of Oxygen
Without oxygen at the bottom of the water body, anaerobic bacteria (those that live without oxygen) produce
acids. These acids not only increase acidity, but also cause a massive release of phosphorus and nitrogen, two
major fertilizers, from the organic sediment and into the water column.
1. • These same anaerobic bacteria put toxic gases in the water including hydrogen sulfide (that rotten egg
smell), ammonia, carbon dioxide and methane. These gases are all toxic to fish, beneficial bacteria and insects.
2. • Lack of bottom oxygen is the cause of odors produced by anaerobic bacteria.
3. . • Lack of fish enables disease-hosting mosquitoes to thrive, as mosquitoes are natural food for fish.
4. • Without oxygen at the bottom at all times, beneficial bacteria and insects cannot biodegrade the organic
sediment. Large accumulations of organic sediment follow.