Nitrogen comprises 78.08 % of the atmosphere making it the largest constituent of the gaseous envelope that surrounds the Earth.

Nitrogen is important in the make up of organic molecules like proteins and DNA.

Most organisms cannot use nitrogen in this form, i.e N2

Plants secure their nitrogen in “fixed” forms i.e incooperated in compounds such as:Nitrate ions NO3

Ammonia NH3

Urea (NH2)2CO

Animals secure their nitrogen (and all other compounds from plants (or animals that have eaten plants).

Four processes participate in the cycling of nitrogen in the biospere:

1. Nitrogen fixation2. Decay3. Nitrification4. Denitrification

*microorganisms play major roles in all processes*

The nitrogen molecule is quite inert. To break it apart so that its atoms can combine with other atoms requires the input of substantial amounts of energy.

inert-non reactive gas during chemical synthesis, analysis or preservation of reactive materials

Three processes are responsible for most of the nitrogen fixation:

1. Atmospheric fixation2. Biological fixation3. Industrial fixation

The enormous energy of lightening breaks nitrogen molecules and enables then to combine with oxygen in the air forming nitrogen oxides.

These dissolve in rain forming nitrates that are carried to the earth.

*contributes 5-8% of total fixed*

Made synthetically via Haber Process.

Nitrogen and hydrogen reacted under great pressure and temperature in the presence of a catalyst to make ammonia.

Ammonia applied directly to farm fields as fertilizers or further processed with oxygen to make nitric acid.

The ability to fix nitrogen is found only in certain bacteria and archaea.

Some live in symbiotic relationship with plants of the legume family Rhizobium

Some establish symbiotic relationships with animals

Some live free in soil

Biological nitrogen fixation requires a complex set of enzymes and a huge expenditure of ATP

Protein made by plants enter and pass through food webs at each level.

At each trophic level metabolism produces nitrogen compounds that return to the environment in excretions.

Microorganisms break down the molecules in excretion and dead organisms into ammonia, NH3.

Most of the ammonia produced by decay is converted into nitrates.

Bacteria of the genus Nitrosomonas oxidize NH3 nitrites NO2

Bacteria of the genus Nitrobacteroxidize nitrites nitrates NO3

This is the reduction of nitrates to nitrogen gas, thus replenishing the atmosphere

Anaerobic bacteria use nitrates as an alternative to oxygen in their respiratory process.

Closing the nitrogen cycle

A side product of this reaction is known as nitrous oxide N2O, more commonly known as “laughing gas”

A mild anesthetic, also a greenhouse gas that contributes to global warming,

Carbon, C is one of the most common elements on Earth.

Its found:1.in the tissues of living organisms2.in the atmosphere3.dissolved in ocean water and 4.locked up in limestone deposits that

line the ocean floor

Living organisms provide two important steps in the carbon cycle.

1.Plants absorb CO2 from the atmosphere to use during photosynthesis

2.Other organisms release CO2 into the air during respiration

In addition there are several important non-organic storage areas of carbon in the environment:

1.A large portion is stored in rocks2.Oceans hold a large amount of CO2

because it dissolves easily in water3.Coal, oil and limestone store carbon

that once form ancient organisms

**burning fossil fuels will release CO2 into the atmosphere**

Photoautotrophs constantly remove carbon dioxide through the process photosynthesis.

Certain bacteria known as chemoautotrophs use carbon dioxide to synthesize the organic compounds they need.

The carbon present in food made by plants reaches animals through the food chain.

Carnivorous animals receive this carbon when they eats animals.

Carbon dioxide is continuously dissolved in water bodies by diffusion.

Once dissolved it either remains in the waters or gets converted into carbonates CO3 and bicarbonates HCO3

-2

The dissolved carbon dioxide is used by plants for photosynthesis.

The carbonates are converted into calcium carbonate by certain marine organisms.

The calcium carbonate is used by corals and oysters to make their shells.

When these organisms die their shell deposit to the sea floor and eventually turn into sedimentary rocks.

When plants and animals die and get buried under the ground, after millions of years they change into fossil fuels due to high pressure and other physical and chemical changes.

Carbon dioxide is regularly returned to the atmosphere by the process of respiration in plants and animals.

Burning of wood and fossil fuels in industry and automobiles also releases carbon dioxide.

It absorbs infrared light. The atmosphere absorbs more heat than i