The Nitrogen Cycle Name: _________________________ Pd. ___

Nitrogen is needed in cells to make:

• 1. Amino Acids which are the building blocks of proteins

  • Build our bodies

    • Ex. Hormones help coordinate bodily functions

• Our body is 60% water and 20% protein

• Act as enzymes to carry out biochemical reactions.

• 2. Nucleotides, which are the building blocks of DNA

  • DNA carries the code to build proteins, which build cells

  • DNA is also the molecule of heredity, allowing the passing down of genes from generation to generation 

Earth’s Atmosphere 

• The atmosphere is nitrogen’s biggest reservoir 

Important Concept

• Nitrogen gas (78%) is everywhere! But…it is like this person having unlimited access to seawater while stranded in his boat.

• Explanation:

  • In biology, changing atoms from a gas into a solid is called “fixing”

  • Our bodies can breathe in oxygen gas and fix it in cell respiration (to water), but we can’t do the same with nitrogen gas…we just don’t have the enzymes!

  • Who does???... Bacteria!

    • Therefore, all plants and animals ultimately depend on them living in the soil for nitrogen

    • This is also why nitrogen is a limiting factor (scarce but vital) for plants  

The Nitrogen Cycle 

Human Impact on The Nitrogen Cycle 

1. Soil Erosion/Degradation 

• Nitrogen is already a limiting factor for plants 

• As crops are grown for agriculture, nitrates in the soil are “used up” and not available for the next year’s plants

• Tilling disrupts the natural microbiome of the soil, sometimes completing eradicating nitrogen-fixing bacteria over time

• These factors result in an already limiting factor becoming even more limiting

2. Fertilizers 

• Farmers add fertilizer to crops to supplement nitrogen (and phosphorous)

• Fertilizer use increased has over time as soils are degraded

• Fertilizer labels will tell you what percent of each limiting factor is contained in the product in order of most limiting to least (pic)

• Fertilizer Run-Off

  • When it rains, some fertilizer surface runoff occurs and ends up in local waters

  • Nitrogen and phosphorous are also limiting factors for algae and so exposure to an excess of these nutrients causes their population to soar  → Algae Bloom 

  • Eutrophication: a nutrient-rich body of water 

  • The algae will soon use up all the nitrogen and phosphorous and die as quickly as they bloomed 

  • Decompostion of the algae by bacteria will suck up oxygen in the water (remember, oxygen is a reactant in cell respiration)

  • Dead/Hypoxia zones: when aquatic-life dies from lack of oxygen

  • The algae bloom can also become so thick that it blocks sunlight from reaching other producers

3. Burning of Fossil Fuels 

• Releases nitrogen oxides into the atmosphere

• This results in:

  • Acid Rain

  • Photochemical Smog

    • Ex. Los Angeles Smog: worse in the morning during rush hour

The Phosphorous Cycle 

• Phosphorous is needed in cells to make… 

  • 1. ATP (adenosine triphosphate)

    • The currency for energy in all cells!

  • 2. (DNA)…again

• The slowest of the cycles because the lithosphere is a slow cycle 

• No atmospheric component

• These two characteristics make phosphorous (like nitrogen) a limiting factor for plants 

  • Terrestrial Producers: nitrogen is most limiting 

  • Aquatic producers: phosphorus is more limiting

• This is also why fertilizers contain nitrogen AND phosphorous

• Human Impact:

  • Fertilizer run-off,  Eutrophication,  Depletion of oxygen, Dead zones