Nitrogen Cycle Processes and Concepts

Why is it essential for matter to be reused and recycled on Earth?

• To prevent the Earth from expanding

• Because the Earth is finite

• To create new types of matter

• To increase the Earth's mass

Which of the following essential biological molecules requires nitrogen?

• Carbohydrates

• Lipids

• DNA

• Water

Approximately what percentage of Earth's atmosphere is composed of nitrogen gas (N2)?

• 21%

• 50%

• 78%

• 99%

Why is nitrogen gas (N2) from the atmosphere not directly usable by most living organisms?

• It is too heavy

• It has a strong triple bond that is hard to break

• It is a noble gas

• It is toxic to living cells

Which type of organisms is primarily responsible for converting atmospheric nitrogen gas into a usable form for plants?

• Fungi

• Nitrogen-fixing bacteria

• Algae

• Viruses

What is the process called where nitrogen gas (N2) is converted into ammonia (NH3) or ammonium (NH4+) in the soil?

• Nitrification

• Denitrification

• Assimilation

• Nitrogen Fixation

What is the process called when plants take up ammonia or nitrates from the soil to build their own biological molecules?

• Respiration

• Photosynthesis

• Assimilation

• Decomposition

Which process involves bacteria converting ammonia (NH3) into nitrites (NO2-) and then into nitrates (NO3-)?

• Ammonification

• Nitrification

• Denitrification

• Nitrogen Fixation

When dead organisms and waste products are broken down, returning nitrogen to the soil as ammonia, what is this process called?

• Nitrification

• Denitrification

• Ammonification

• Assimilation

What is the process by which denitrifying bacteria convert nitrates back into nitrogen gas (N2), releasing it into the atmosphere?

• Nitrogen Fixation

• Nitrification

• Denitrification

• Ammonification