Nitrogen cycle

Organisms need nitrogen in order to...

• To breathe

• To obtain water for growth

• To build proteins & DNA

• To regulate temperature

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

Nitrogen accounts for what percentage of the air in the atmosphere?

• 42%

• 14%

• 95%

• 78%

Which molecular formula is atmospheric nitrogen?

• NH4

• NO2

• N2

• NO3

• NH3

Plants and animals cannot use nitrogen directly from the air.

• True
• False

Bacteria fix nitrogen from the atmosphere into a form plants can use.

• True

• False

​ ​ ​ (a)   is the conversion of soil Nitrogen (NO3) into Nitrous oxide (N2O) gas which returns to the ​ (b)   .

• Denitrification
• atmosphere
• soil
• Assimilation
• Nitrification

​ ​ (a)   is when bacteria, microbes, and other decomposers convert waste and dead biomass into NH3 and return it to the ​ (b)   .

• Ammonification
• soils
• Nitrification
• atmosphere
• Assimilation

Click the blank that labels Assimilation.

​ (a)   is the conversion of NH4 into nitrite (NO2) & then nitrate (NO3) by ​ (b)   .

• Nitrification
• soil bacteria
• Denitrification
• Assimilation
• plants
• animals