Lesson 5.6 - Nitrogen Cycle: Part 3

You have learned that nitrogen is fixed into nitrates by lightning and by nitrogen-fixing bacteria.  You have learned that plants use nitrates to obtain the nitrogen needed to build plant cells.  Animals eat the plants to obtain the nitrogen they need for their cell growth. 

All organisms produce wastes and die.  Bacteria decompose the wastes and bodies of the organisms.  One of the products of decomposition is ammonia, which is a nitrogen containing compound.  Ammonia is converted to nitrates by bacteria and the nitrates are then available to plants.  That completes the nitrogen cycle, right?  You should have said No! 

A cycle means that things are returned to their original state as well.  Where are the nitrates converted back to nitrogen N2(g)?  There seems to be a step missing here.  You are right, there is a step missing.  There are bacteria that convert nitrates into atmospheric nitrogen, N2(g), which completes the cycle.

Now, answer the following questions.

 

Question 1. What nitrogen compound is produced when bacteria break down wastes and plant and animal bodies?

Question 2. What do bacteria break ammonia down into?

Question 3. What is another product when bacteria break nitrates down?

Question 4. You now know the complete nitrogen cycle.  Make a sketch of the nitrogen cycle and include the following terms:

        • atmospheric nitrogen
        • lightning
        • legumes
        • nitrogen fixing bacteria
        • nitrates
        • plants
        • animals
        • animal wastes
        • dead plants and animals
        • bacteria
        • ammonia

 

Check your answers with those that follow.

 

 

 

 

 

 

 

 

 

 

 

 

Answers to Questions:

Question 1. What nitrogen compound is produced when bacteria break down wastes and plant and animal bodies?

Ammonia is produced when bacteria break down wastes and plant and animal bodies.

Question 2. What do bacteria break ammonia down into? 

Bacteria break ammonia down into nitrates.

Question 3. What is another product when bacteria break nitrates down?

Nitrogen gas is another product of nitrate decomposition.  Note that there are other steps in the process that are beyond the scope of the course.  You may want to look at some websites that cover the nitrogen cycle in more detail.  

Question 4. You now know the complete nitrogen cycle.  Make a sketch of the nitrogen cycle and include the following terms:

        • atmospheric nitrogen
        • lightning
        • legumes
        • nitrogen fixing bacteria
        • nitrates
        • plants
        • animals
        • animal wastes
        • dead plants and animals
        • bacteria
        • ammonia

Here are some possible ways of diagramming the nitrogen cycle.

 

 


Go to the next page to continue Lesson 5.