The Nitrogen Cycle

The Nitrogen Cycle:

Nitrogen is used to make proteins and other substances for organisms as they grow. Plants and animals get nitrogen from nitrogen-containing substances. Plant roots absorb nitrogen compounds from the soil and use them to make nitrogen compounds in their biomass.

Animals get nitrogen compounds in their food. Most of which are sued to make nitrogen compounds in new biomass but some are lost in faeces and urine.

Plants would die out if there wasn't a way to convert nitrogen compounds back to nitrates in the soil.. So when decomposers feed on waste they break down some proteins and urea (a nitrogen rich substance in urine) to ammonia and release it in the soil.

The soil contains nitrogen-fixing bacteria that fixes nitrogen gas into ammonia.

In legume roots  mutualistic nitrogen-fixing bacteria is found. This bacteria lives inside root nodules and provide plants directly with ammonia.

Plants grow better with nitrates. So some nitrifying bacteria in soil converts ammonia to nitrates.

If soil starts lacking in oxygen the dentrifying bacteria will convert nitrates back to nitrates and others convert nitrates back to nitrogen gas.

Lightning can occasionally provide energy to combine oxygen and nitrogen gases in the air that quickly form nitrates.

Key Words:

Urea

Nitrogen-fixing bacteria

Root nodules

Nitrifying bacteria

Denitrifying bacteria

Questions:

1. Why are decomposers important in the nitrogen cycle?

2. Why does adding manure to soil increase the nitrate content?

What you should know:

An understanding of how nitrogen is recycled:

a. nitrogen gas in the air cannot be used directly by plants and animals.

b. nitrogen-fixing bacteria living in root nodules or the soil can fix nitrogen gas

c. the action of lightning can convert nitrogen gas into nitrates

d. decomposers break down dead animals and plants

e. soil bacteria convert proteins and urea into ammonia

f. nitrifying bacteria convert this ammonia to nitrates

g. plants absorb nitrates from the soil

h. nitrates are needed by plants to make proteins for growth

i. nitrogen compounds pass along a food chain or web

j. denitrifying bacteria covert nitrates to nitrogen gas