Think of a deer in the woods that has just relieved itself by urinating. number the steps to follow the nitrogen molecules in the urine as they go through the nitrogen cycle. 1. step 1 ammonium can be absorbed by plants, but some is converted into nitrates which are better for plants to absorb. this is called nitrification. 2. step 2 the deer eats the plants and uses the nitrogen-containing proteins for cell growth. 3. step 3 bacteria in the soil conduct nitrogen fixation to convert nitrogen gas from the atmosphere into ammonium. 4. step 4 some of the nitrates are absorbed back into plants, but denitrification breaks down the nitrates into nitrogen gas released back into the atmosphere. 5. step 5 nitrogen is found in the urine, which gets broken down into ammonium through the process of ammonification. 6. step 6 plants absorb the ammonium and begin assimilation, the process to add the nitrogen to protein.

The molecules of nitrogen in the urine are broken down into ammonium. - Step 5 ("Nitrogen is found in the urine, which gets broken down into ammonium through the process of ammonification.")
Then, ammonium is converted into nitrates by nitrifying bacteria. - Step 1 ("Ammonium can be absorbed by plants, but some is converted into nitrates which are better for plants to absorb. This is called nitrification.")
There are then two ways that the cycle can take... in the one related to the deer, follows the assimilation where the plants add the nitrogen to protein. - Step 6 ("Plants absorb the ammonium and begin assimilation, the process to add the nitrogen to protein.")
The deer then eats the plants and the nitrogen is again inside it and ready to be used and again released in urine. - Step 2 ("The deer eats the plants and uses the nitrogen-containing proteins for cell growth.")

The other way that the nitrogen may take is denitrification by denitrifying bacteria. - Step 4 ("Some of the nitrates are absorbed back into plants, but denitrification breaks down the nitrates into nitrogen gas released back into the atmosphere.")
This gas is then captured by nitrogen fixing bacteria, called nitrogen fixation. - Step 3 ("Bacteria in the soil conduct nitrogen fixation to convert nitrogen gas from the atmosphere into ammonium.")
The ammonium is now ready again for the process of ammonification.

Because the carnivores keep the herbivore population in check