Big on Biology The Nitrogen and Phosphorus Cycled 9-12 Science Std: Bio 6d, Geo 7a,b,c

C.NITROGEN CYCLE Nitrogen (N 2 ) is basic building block for life. It is a colorless, odorless, and nontoxic gas. Nitrogen is found mostly in: Nitrogen (N 2 ) is basic building block for life. It is a colorless, odorless, and nontoxic gas. Nitrogen is found mostly in:  All DNA  Animal protein  Atmosphere (78%!)

N 2 is a very stable molecule, so is hard to take out of atmosphere. It has to be taken out and then used in another form called nitrate (NO 3 ). N 2 is a very stable molecule, so is hard to take out of atmosphere. It has to be taken out and then used in another form called nitrate (NO 3 ).  Conversion of nitrogen (N 2 ) to nitrate (NO 3 ) is called nitrogen fixation. o How does it get converted to nitrate? Lightning Bacteria in soil Nitrogen fixing bacterium Azospirrillum found soils.

Lightning This method does not happen often, since lightning doesn’t occur often. Energy from lightning causes N 2 gas to react with O 2 in the air, producing NO 3 Nitrates dissolve in rain, then fall to Earth, enter the soil, then move into plants through their roots. Plants use nitrates to make their own DNA, and to make amino acids which make proteins.

Bacteria in Soil Since there is a lot of bacteria around, this is how most nitrates are produced Bacteria are found in small lumps or nodules on the roots of most plant legumes like clover, soybeans, peas, and alfalfa. nodules

clover soybeans peas alfalfa LEGUMES

These give the plant built-in supply of usable nitrogen to help plants grow, while plant gives bacteria sugar they need to make nitrates. Farmers usually rotate crops – first crop uses up nitrogen, next legume crop replenishes nitrogen, third crop uses up nitrogen again, over and over Uses NO 3 Makes NO 3

Crop Rotation Uses nitrates Makes nitrates Uses nitrates Makes nitrates

Conversion of nitrate (NO 3 ) back to nitrogen (N 2 ) is called denitrification and takes a couple of steps by different bacteria: Conversion of nitrate (NO 3 ) back to nitrogen (N 2 ) is called denitrification and takes a couple of steps by different bacteria:  First NO 3 has to be converted to nitrite (NO 2 )  NO 2 is converted to N 2 and released back into atmosphere Gets recycled again and again in the nitrogen cycle Gets recycled again and again in the nitrogen cycle

N 2 Nitrogen gas NITROGEN FIXATION fertilizers decomposers Nitrogen in protein bacteria NO 3 & NO 2 Nitrates & Nitrites feeding DENITRIFICATION NITROGEN FIXATION

The Nitrogen Cycle N 2 In Air Denitrification Fertilizer Factory Fixation (Lightning) N Fixing Bacteria NO 3 Nitrate Bacteria NO 2 Nitrite Bacteria NH 4 + Decomposers Decay and Waste PlantsAnimals Bacteria in Nodules

D.PHOSPHOROUS CYCLE Phosphorus (P) is not found in the atmosphere but is found in Earth- bound matter Phosphorus (P) is not found in the atmosphere but is found in Earth- bound matter  In living things, its found in DNA, bones, and shells o Short cycle since it doesn’t take long (few months) for phosphorus to become a part of a living creature

 In non-living rocks due to other fossils being trapped in sediment during the rock cycle oLonger cycle since it takes a long time for rocks to form (millions of years)

Phosphorus (P) tends to combine with oxygen (O 2 ) to form phosphate (PO 4 ) ions. Phosphorus (P) tends to combine with oxygen (O 2 ) to form phosphate (PO 4 ) ions.  Can be removed from dead organisms by decomposing bacteria

 Are soluble (dissolvable) in water, so they can be drawn (taken) out of rock by weathering and become part of the water cycle oNow can be absorbed by plants and phytoplankton to enter food sources PO 4

weathering PO 4 decomposers P P PHOSPHOROUS CYCLE

E.AGRICULTURE AND NITROGEN AND PHOSPHOROUS CYCLES Seeds, leaves, flowers, and fruits of plants contain valuable nutrients, which is why we eat them. But as crops are harvested, valuable nitrogen and phosphorous in these plant parts get removed and do not return to the soil they came from Seeds, leaves, flowers, and fruits of plants contain valuable nutrients, which is why we eat them. But as crops are harvested, valuable nitrogen and phosphorous in these plant parts get removed and do not return to the soil they came from

 This removal of nitrates and phosphates from the soil make it almost impossible to grow crops again since it has no nutrients for the seeds.

o This is why farmers use fertilizers that contain nitrates and phosphates in their soil. Estimated that these can DOUBLE the amount of cereal crops like wheat and barley. + fertilizer

Hey, if a little fertilizer can produce double the amount, shouldn’t a lot produce more? More is not necessarily better

Spring rains on the farms make water run off into rivers, lakes, streams, or oceans. That water now contains nitrogen and phosphates from all that fertilizer. Spring rains on the farms make water run off into rivers, lakes, streams, or oceans. That water now contains nitrogen and phosphates from all that fertilizer.  These extra nutrients in the water cause algae and other aquatic plants like seaweed to grow like crazy – this is called algal bloom.

Algal Bloom

o Once these plants die, bacteria that decompose them need to use extra oxygen from the water to do so. Use of too much oxygen from water will kill fish and the animals that eat fish! Dead fish means more bacteria to decompose them, which use more oxygen, which means more dead fish!

o The End???????