L7.1.4: The Nitrogen Cycle

What do you already know about the nitrogen cycle?

Why is atmospheric nitrogen (N2) not directly usable by most living organisms?

• It is too abundant in the atmosphere.

• It has a strong triple bond that is difficult to break.

• It is a noble gas and does not react.

• It is only found in the upper atmosphere.

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What is the process by which nitrogen-fixing bacteria convert atmospheric nitrogen gas (N2) into ammonia (NH3) or ammonium (NH4+)?

• Nitrification

• Denitrification

• Nitrogen Fixation

• Ammonification

Which process involves nitrifying bacteria converting ammonia into nitrites and then into nitrates?

• Assimilation

• Denitrification

• Nitrogen Fixation

• Nitrification

What happens to nitrogen when living organisms die and decompose?

• It is immediately released back into the atmosphere as N2 gas.

• It is converted into nitrates by nitrifying bacteria.

• It is returned to the soil as ammonia through ammonification.

• It is assimilated directly by other living plants.