Cycles Worksheet
Answer the following using the words in the text box.
Carbon Cycle
1. Plants use CO2 in the process of ___________________ to make ___________ and oxygen.
2. Animals use oxygen in the process of _______________ and make more CO2.
3. The ____________ is the main regulator of CO2 in the atmosphere because CO2 dissolves
easily in it.
4. In the past, huge deposits of carbon were stored as dead plants and animals __________.
5. Today these deposits are burned as fossil fuels, which include _____________,
_______________, and ______________.
6. More CO2 is released in the atmosphere today than in the past because of _________
___________________ .
7. Another natural source for CO2 is __________________.
8. Too much CO2 in the atmosphere may be responsible for the _______________ effect.
9. Write the equations for photosynthesis and respiration.
Nitrogen Cycle
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
Atmosphere 78% ammonia proteins denitrificating
Nitrate nitrogen-fixing plants animals waste plants
Coal Oil Natural Gas burning of fossil fuels volcanoes Photosynthesis
Respiration ocean sugar Greenhouse decayed
