A BRIEF OVERVIEW OF THE PREVIOUS CLASS: (01:06:00 PM)

• Biogeochemical Cycles.

SULFUR CYCLE: (01:11:00 PM)

• Sulfur is a very important macronutrient in plants.
• Plats directly take a very small amount from the air in the form of sulfur dioxide(SO2).
• However, the major source is sulfate Ions from the soil.
• Note:
• Gaseous Cycle:
• Whenever an element is taken by the life forms in the form of gases, and it majorly moves through the gases in the ecosystem, then it is called a gaseous cycle. 
• For example, Carbon, Water Cycle, etc.
• Sedimentary Cycle: 
• Whenever an element is taken by the life forms in the solid form, and it majorly moves through the solid states in the ecosystem, then it is called a sedimentary cycle. 
• Pool: 
• It is a body in which an element is present in a concentrated form in an ecosystem.
• For example, rocks, water bodies, soil, and atmosphere are examples of pools.
• Sources of Sulfur:
• Volcanic Eruption- Volcanic eruption releases Sulfur, H2S, and SO2 in the environment.
• Minerals and rocks-  for example, Pyrite(FeS2, Fool's Gold)
• Chemical Actions in rock -> SO2 to the atmosphere.
• Bruning of fossil fuels -> SO2, H2S, etc.
• Industries like oil refineries, Paper, & chemical industries release huge amounts of H2S.
• Forest fires release Ammonium Sulfate.
• Mycorrhiza fungi which are attached to the plant's roots decompose dead plant or animal material and release sulfate ion that is taken by the plant's roots.
• Aspergillus is one very important fungi in decomposing organic matter( dead plant or animal material).
• Decay of dead plant or animal material -> Hydrogen sulfide(H2S).
• Bacterias convert this H2S to Sulfate Ions. Most important bacteria is Thiobacillus.
• Sulfate ions can be reconverted into H2S by another class of bacteria like Salmonella.
• H2S reacts with Oxygen in the atmosphere to produce SO2 which then can react with water/snow and come to the ground as Sulfuric Acid -> Wet Deposit.
• SO2 can also react with Oxygen to produce Supfate ions which come directly as dust to the surface known as Dry Deposit.
• Sulfate reacts with water and forms Sulfide which is absorbed by rocks or minerals and deposited.

NITROGEN CYCLE: (02:22:00 PM)

• Nitrogen molecules are very stable and can't be taken by life forms directly from the atmosphere. 
• N2 is a chemically inert gas.
• Nitrogen is very important for living beings as it is required in pricing Amino acids, DNA, etc.
• Nitrate Ions(NO3) Ions are the most important form which is taken up by living beings.
• Sources of Nitrogen to the Atmosphere:
• Volcanic eruptions- Oxides of Nitrogen.
• Bacterial decomposition of plants and animal material -> Oxides of Nitrogen mainly N2O(Nitrous Oxide) and NO(Nitric Oxide).
• Breakdown of nitrogenous fertilizers ->  Oxides of Nitrogen.
• Fossil Fuel burnings(Minaly automobile exhaust) produce N2O(Nitrous Oxide) and NO(Nitric Oxide).
• Coal Burning -> Most importantly NO(Nitirc Oxide).
• By lightening: 
• N2+ O2 -> Oxides of Nitrogen -> Nitrate (NO3-) -> Settles on Earth's surface as dust- Dry deposition.
• Nitrate + Water -> HNO3(Ntiric Acid) comes with rain - Wet deposition.
• Nitrogen Fixation: 
• It is the production of Ammonia(NH3) or Ammonium(NH4-) by the nitrogen-fixing bacteria & algae which decompose dead animal and plant matter.
• These microorganisms are close to the roots of the plants to get their carbon which is released by plant roots.
• When these algae and bacteria decompose dead organic matter  Ammonia(NH3) or Ammonium(NH4-) are produced.
• Algae Like Nostoc and Bacteria like Azaztobacter, Clostridium produce Ammonia(NH3) or Ammonium(NH4-).
• Nitrification:
• Biological conversion of Ammonia(NH3) or Ammonium(NH4-) into Nitrite(NO2-) and Nitrates(NO3-).
• Ammonia is first converted into Nitrite(NO2-) by bacteria like Nitrococus & Nitrosomonas.
• Then Nitrite(NO2-) is converted into Nitrate(NO3-) by a bacteria Nitrobactor -> Plants -> Animals.
• Immobilization- It s when the nitrates are taken up by the rocks or minerals.
• Denitrification:
• It is the biological conversion of Nitrate into Nitrogen (N2) by a sequence of stages.
• It is done by a bacteria called Pseudomonas.
• Nitrates(NO3-) -> Nitrite(NO2-) -> Nitirc Oxide(NO) -> Dinitrogen(N2). 

CARBON CYCLE: (03:38:00 PM)

• Carbon is one of the most important elements of organic life.
• A very small amount of Carbon(only about 2% of the total Carbon) is part of the Biogeochemical cycle.
• Sources of Carbon:
• Breakdown of rocks & release of CO2.
• Volcanic eruptions.
• Decay and decomposition of organic materials.
• Combustion of fossil fuels.
• Respiration by animals and plants.
• Forest fires. etc.
• Carbon is removed from the atmosphere by:
• Formation of Coal deposits.
• Absorption by water and ice.
• Photosynthesis by Plants.
• Oxygen Cycle:
• 99.5% of the total Oxygen by mass is locked in the Earth's Crust.
• Only 0.5% of the Oxygen is present in the atmosphere.
• Sources of Oxygen:
• Breakdown of minerals.
• Release by Plants during Photosynthesis.
• Volcanic Activity.
• Photolysis of water by UV rays. etc.
• Removal of Oxygen:
• Respiration by plants & animals.
• All combustion processes.
• Absorption by water bodies, etc.

TOPICS FOR THE NEXT CLASS: Ecological Succession, Biomes, etc.