What are two key nutrients that are abundant on Earth but often not in a bioavailable form for organisms?

• Oxygen and Carbon

• Nitrogen and Phosphorus

• Water and Carbon

• Hydrogen and Oxygen

What percentage of an animal's body is typically composed of nitrogen?

• 65%

• 19%

• 10%

• 3%

Which of the following biological molecules requires phosphorus for its structure or function?

• Amino acids

• Proteins

• DNA

• Carbohydrates

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

• It is too heavy

• It is a noble gas

• It has a strong triple bond

• It is too rare

What is the process called where atmospheric nitrogen is converted into a usable form for plants?

• Denitrification

• Nitrification

• Nitrogen fixation

• Ammonification

Which enzyme is responsible for breaking the triple bond in atmospheric nitrogen (N2) during nitrogen fixation?

• Amylase

• Nitrogenase

• Lipase

• Protease

What is the role of nitrifying bacteria in the nitrogen cycle?

• Convert nitrates into atmospheric nitrogen

• Convert atmospheric nitrogen into ammonia

• Convert ammonia into nitrates and nitrites

• Break down dead organic matter

Besides nitrogen-fixing bacteria, what other natural phenomenon can break the strong bonds of atmospheric nitrogen, making it available for conversion?

• Volcanic eruptions

• Forest fires

• Lightning

• Earthquakes

What enzyme do denitrifying bacteria utilize to convert nitrogen oxides back into nitrogen gas?

• Nitrogenase

• Nitrite reductase

• Nitrate reductase

• Ammonia monooxygenase

Which of the following elements, when cycling through ecosystems, does not primarily involve the atmosphere?

• Carbon

• Nitrogen

• Phosphorus

• Oxygen