Question

nitrogen cycle
atmosphere 78% ammonia proteins denitrifying
nitrate nitrogen - fixing plants animals waste plants

1. our atmosphere is ______ nitrogen gas.
2. animals and plants cannot directly use all the nitrogen found in our ______.
3. only special bacteria can directly use nitrogen in our atmosphere and \fix\ it so other organisms can benefit. these bacteria are called ____ - ____ bacteria.
4. higher organisms use nitrogen to make their ______.
5. animal waste decay by the action of bacteria which create ____ and ____ products rich in nitrogen, and useful for plants to use again.
6. ______ bacteria in the soil can break down the ammonia into the gaseous form of nitrogen, which is not available for use by plants or animals.
7. in another part of the cycle, animals eat ____ containing nitrogen, which is again returned to the soil by animal __ or decaying __ and ____.
8. draw a diagram of the nitrogen cycle using the words in the text box.

Explanation:

1. The atmosphere is 78% nitrogen gas.
2. Animals and plants can't directly use atmospheric nitrogen.
3. Nitrogen - fixing bacteria convert atmospheric nitrogen for other organisms.
4. Higher organisms use nitrogen for proteins.
5. Animal waste decay by bacteria creates ammonia and nitrogen - rich products.
6. Denitrifying bacteria break down ammonia into gaseous nitrogen.
7. Animals eat plants containing nitrogen, which returns to soil via waste or decaying plants and animals.
8. Diagram should show the cycle of nitrogen among atmosphere, plants, animals, bacteria, and waste using given words.

Answer:

1. 78%
2. atmosphere
3. nitrogen - fixing
4. proteins
5. ammonia; nitrogen - rich
6. Denitrifying
7. plants; waste; plants; animals
8. (Explanation for drawing: Start with the atmosphere having 78% nitrogen. Show nitrogen - fixing bacteria converting nitrogen for plants. Plants are eaten by animals. Animal waste decays to form ammonia and nitrogen - rich products. Denitrifying bacteria convert ammonia back to gaseous nitrogen in the atmosphere. The cycle repeats.)