BIOGEOCHEMICAL CYCLES

The flow of energy in the biosphere is in one direction only: from the sun, through living organisms, into the environment, and out into space. Matter cycles constantly from organism to organism as well as to and from the environment, which acts as a reservoir.

The cyclic pathways taken by various elements in passing through living organisms (biotic) and the earth, its atmosphere and its bodies of water (abiotic) are generally called biogeochemical cycles. The NITROGEN CYCLE is one of the most important.

Proteins and nucleic acids are essential to life. In order to make them, living things must obtain nitrogen in a useable form. Nitrogen in the air is diatomic (“2-atom”) molecules N 2, and no animal or plant can separate them to use them. To be useful the nitrogen must be “fixed”=be attached to atoms of some other elements to form a compound.

Nitrogen fixation….. Can occur by: Passage of UV light and lightning through the air = NO 3 - (nitrate ions) formed Volcanoes, combustion of fossil fuels (coal, oil, natural gas) and forest fires = nitrate and NH 3 (ammonia) Rain brings the fixed nitrogen to the soil as NH 4 - (ammonium ion)

The bulk of this is carried out by nitrogen- fixing bacteria in soil and by cyanophytes (blue-green bacteria). The most efficient nitrogen fixers are bacteria found in nodules on the roots of certain plants, notably the legumes (alfalfa, beans, peas, lentils, clover). Fertilizers also add nitrogen to the soil

Animals must consume Nitrogen in the form of already formed amino acids in their food. Excretions of animals and the dead bodies of all organisms are broken down in the soil by decomposers in the process of ammonification, which produces ammonia.

Nitrifying bacteria convert the ammonia to NO 2 - (nitrite ion), then another group of nitrifying bacteria convert the nitrite ion to NO 3 - (nitrate ion). This is know as nitrification. Nitrate is readily taken up by roots of plants and utilized.

Denitrifying bacteria convert nitrate to N 2 O (nitrous oxide) or N 2 (nitrogen gas), which is then lost to the atmosphere. Nitrogen is lost from soil by erosion and carried into streams, rivers, and ultimately the ocean. It then cycles through aquatic organisms. Eventually, some nitrogen is lost to sediments at the bottoms of oceans or lakes.

Assignment: 1)Diagram and label one of the Biogeochemical Cycles. (pg ) 2)Provide a caption under it explaining what is occurring. 3)Answer Section 4 Review (questions 1-8) on pg. 374.(due by end of class on Wed.. 9/8) Finish your Energy Pyramid model first