The NITROGEN CYCLE

​The NITROGEN CYCLE

Animals get their nitrogen compounds from plants (or animals that have fed on plants).

Five processes participate in the cycling of nitrogen through the biosphere:

(1) nitrogen fixation,

(2) decomposition,

(3) nitrification,

(4) denitrification,

(5) assimilation.

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​The nitrogen cycle is a repeating cycle of processes during which nitrogen moves through both living and non-living things:

the atmosphere, soil, water, plants, animals and bacteria.
In order to move through the different parts of the cycle, nitrogen must change forms.

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​1. NITROGEN FIXATION: Fixation converts 'free' nitrogen (N2) in the atmosphere into forms that plants can absorb through their root systems.

• A small amount of nitrogen can be fixed when LIGHTNING provides the energy needed for N2 to react with oxygen.

• NITROGEN-FIXING BACTERIA invade the root hairs of plants, where they multiply and stimulate formation of root nodules. Within the nodules the bacteria convert Atmospheric Nitrogen (N2) to ammonia (NH4), which plants use.

​2. DECOMPOSITION: Decay or decomposition is the process where DECOMPOSERS (bacteria and fungi) break down organic nitrogen compounds in dead remains, feces and urine to give ammonia.

• Decomposition produces ammonia, which can then go through the nitrification and denitrification process.

​3. NITRIFICATION: Nitrification is the process that converts ammonia to nitrite and then to nitrate and is carried out by bacteria.

​4. DINITRIFICATION: Denitrification is the process that converts nitrate to nitrogen gas by bacteria, thus removing bioavailable nitrogen and returning it to the atmosphere.

​5. ASSIMILATION: Assimilation is the process by which plants and animals incorporate the nitrates and ammonia formed through nitrogen fixation and nitrification. Plants take up these forms of nitrogen through their roots, and incorporate them into plant proteins and nucleic acids.

Labelling

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Assimilation

Atmospheric Nitrogen

Lightning

Ammonia (NH3)

Decomposition

Nitrogen-fixing Bacteria

Nitrates (NO3)

Multiple Choice

Which of the following processes in the nitrogen cycle is the conversion of soil nitrate to the nitrogen gases by bacteria?

• NITROGEN-FIXATION

• DECOMPOSITION

• NITRIFICATION

• DINITRICATION

Multiple Choice

Which of the following processes in the nitrogen cycle is the process where bacteria converts ammonia to nitrite and then to nitrate?

• NITROGEN-FIXATION

• DECOMPOSITION

• NITRIFICATION

• DINITRICATION

Multiple Choice

Which of the following processes in the nitrogen cycle is where decomposers break down animal and plant materials and waste to release energy, releasing a form of ammonium into the soil.

• NITROGEN-FIXATION

• DECOMPOSITION

• NITRIFICATION

• DINITRICATION

Multiple Choice

Which of the following processes in the nitrogen cycle is a process that converts atmospheric nitrogen into ammonia. Performed by nitrogen-fixing bacteria?

• NITROGEN-FIXATION

• DECOMPOSITION

• NITRIFICATION

• DINITRICATION

Multiple Choice

Which process in the nitrogen cycle is occurring when plant roots absorb nitrates?

• nitrogen fixation

• nitrification

• assimilation

• denitrification

Multiple Choice

Known as eutrophication, excess fertilizer runoff in aquatic ecosystems causes -

• too much oxygen in the water

• algae to die

• algal blooms

Multiple Choice

Which abiotic cycle includes lightning?

• water cycle

• carbon cycle

• nitrogen cycle

Multiple Choice

Where are nitrogen-fixing bacteria found?

• in the atmosphere

• on the root nodules of legume plants

• in animal waste

Multiple Choice

Humans add nitrogen to the nitrogen cycle by -

• burning fossil fuels

• cellular respiration

• using fertilizers

Multiple Choice

What is the most abundant gas in the atmosphere?

• Carbon dioxide

• Oxygen

• Nitrogen

Multiple Select

All organisms require nitrogen to build -

[select TWO]

• proteins

• build new cells

• simple sugars

• generate energy

Multiple Select

Which TWO ways can atmospheric Nitrogen be fixed -

[select TWO]

• nitrogen-fixing bacteria

• lightning

• decomposers

• plants

Multiple Choice

Which abiotic cycle is the movement of nitrogen between the land, the oceans, the atmosphere and the Earth's interior?

• rock cycle

• water cycle

• carbon cycle

• nitrogen cycle

Multiple Choice

How do animals get the nitrogen they need?

• from the air they breathe

• from the water they drink

• from the food they eat

• from the Sun

Dropdown

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converts 'free' nitrogen (N₂) in the atmosphere into forms that plants can absorb through their root systems.

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​ Decay or ​

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is the process where decomposers (bacteria and fungi) break down organic nitrogen compounds in dead remains, feces and urine to give ammonia.

Dropdown

​ ​

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is the process that converts ammonia to nitrite and then to nitrate and is carried out by bacteria.

Dropdown

​ ​ ​

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is the process that converts nitrate to nitrogen gas by bacteria, thus removing bioavailable nitrogen and returning it to the atmosphere.

Dropdown

​ ​ ​ ​ ​

Select answer

is the process by which plants and animals incorporate the nitrates and ammonia formed through nitrogen fixation and nitrification. Plants take up these forms of nitrogen through their roots and incorporate them into plant proteins and nucleic acids.