2-3 Nitrogen Cycle

Nitrogen Cycle Nitrogen – production of proteins and

nucleic acids 79% of atmosphere – N2 gas Most plants and animals cannot capture

nitrogen from the atmosphere Plants: Use nitrogen in the form of NO3

-

nitrates to produce amino acids then proteins Animals eat plant protein digest it into

amino acid use amino acids to build animal protein in the cells

Nitrogen Cycle

Nitrogen Fixation

Nitrification

Denitrification

Nitrification Animals produce waste, die and

decay Nitrogen compounds introduced to

soil Bacteria work on compounds

breaking them into ammonium compounds then nitrates

Nitrates are absorbed by plants

Nitrogen Fixation Nitrogen Fixation: process of converting

atmospheric N2 into nitrates (NO3-) and

ammonium ions (NH4+)

Nitrogen-fixing bacteria: found on nodules of roots (legumes, alfalfa) Rhizobium convert N2 to nitrates to be used by plant

plant gives bacteria sugars excess nitrates move into soil

Nitrogen Fixing Bacteria

Rhizobium

Nitrogen Fixation Lightning - N2 reacts with O2

- Nitrates are produced

Nitrates fall to earth, enter soil, move into plants through the roots

Crop rotation - balances input and output of N2

Denitrification Denitrifying bacteria: break down nitrates

and nitrites into N2 gas gas reenters atmosphere Denitrifying bacteria carry out anaerobic

respiration found in tightly packed soil and or water logged soil

Aeration slows down denitrification Allow oxygen entry to soil inhibits

denitrifying bacterial growth Keeps grass green by keeping nitrates in the

soil Nitrates are need for chlorophyll (protein)

production

Nitrogen Cycle Diagram

1 Atmospheric pool of nitrogen2 Nitrogen-fixing bacteria in root nodules of legumes3 Fertilizers4 Soil nitrate5 Nitrate take up by plant roots6 Plant and animal proteins7 Dead organisms8 Decomposers9 Nitrate bacteria10 Nitrate bacteria11 Denitrifying bacteria12 Lightning

Nitrogen Cycle Diagram