Nitrogen Cycle

How much of the atmosphere is composed of nitrogen gas?

• 87%
• 38%
• 78%
• 21%

Organisms that break down dead plants & animals and release nitrogen back into atmosphere...

• bacteria
• plants
• animals
• producers

Organisms that need nitrogen to survive

• only plants
• only animals
• only bacteria
• all living organisms

If the atmosphere is 78% N₂, why can't we just get our nitrogen by breathing?

• We have no mechanism to break the triple bond of nitrogen between the atoms.
• Our lungs would be damaged by the N2.
• We need Oxygen for cellular respiration.
• The legumes take it up first.

Plants and animals cannot use nitrogen directly from the air.

• True
• False

After plants and animals contain nitrogen, what puts it back into atmosphere and soil?

• decomposition
• precipitation
• condensation
• bacteria

_____ is the conversion of organic nitrogen into ammonia

• Nitrogen Fixation
• Ammonification
• Denitrification
• Assimilation 

Which nitrogen cycle process is occurring when plant roots absorb ammonium ions and nitrate ions for use in making molecules such as DNA, amino acids, and proteins?

• nitrogen fixation

• nitrification

• denitrification

• ammonification

• assimilation

Which nitrogen cycle process is occurring when bacteria convert ammonium to nitrite and then into nitrate?

• nitrogen fixation

• nitrification

• denitrification

• ammonification

• assimilation

Which nitrogen cycle process is occurring when nitrogen in plant or animal protein is converted to ammonium?

• nitrogen fixation

• nitrification

• denitrification

• ammonification

• assimilation