4.3 Study Guide
Key facts
1. While energy enters and leaves ecosystems (flowing in one direction), nutrients are recycled
or reused.
2. Common examples of this nutrient recycling include the carbon cycle, the water cycle, the
nitrogen cycle and the carbon cycle.
3. The carbon cycle is a major factor in the greenhouse effect.
4. The carbon cycle represents the interaction of living organisms and the biosphere through the
processes of photosynthesis, cell respiration, fossilization and combustion. 29. Photosynthesis
allows the fixation of carbon dioxide from the atmosphere. Combustion results in the release of
and accumulation of more carbon dioxide in the atmosphere. Respiration results in the release of
carbon dioxide and accumulation in the atmosphere.
5. Decomposers, saprotrophs and detritivores, result in release of carbon dioxide into the
atmosphere, and therefore, the recycling of carbon.
6. Autotrophs convert carbon dioxide into carbohydrates and other carbon compounds.
7. In aquatic habitats carbon dioxide is present as a dissolved gas and hydrogen carbonate ions.
8. Carbon dioxide diffuses from the atmosphere or water into autotrophs.
9. Carbon dioxide is produced by respiration and diffuses out of organisms into water or the
atmosphere.
10. Methane is produced from organic matter in anaerobic conditions by methanogenic
archaeans and some diffuses into the atmosphere.
11. Methane is oxidized to carbon dioxide and water in the atmosphere.
12. Peat forms when organic matter is not fully decomposed because of anaerobic conditions in
waterlogged soils.
13. Partially decomposed organic matter from past geological eras was converted into oil and gas
in porous rocks or into coal.
14. Carbon dioxide is produced by the combustion of biomass and fossilized organic matter.
15. Animals such as reef-building corals and molluscs have hard parts that are composed of
calcium carbonate and can become fossilized in limestone.
Additional skills and questions
17. Be able to analyze date from atmosphere monitoring stations showing annual fluctuations.
18. Draw and label a diagram of the carbon cycle to show the processes involved. Be certain to
include photosynthesis, cell respiration, fossilization, combustion and decomposition.
19. List three sources of carbon dioxide in our atmosphere.
20. What major biological process allows a decrease in atmospheric carbon dioxide
levels?_____________________
21. The Gaia hypothesis views the biosphere on Earth as a single living organism because there
appears to be a significant level of self-regulation. How does the carbon cycle contribute to this
self-regulation?
22. Present some reasons for the increase in carbon dioxide levels in the Earth’s atmosphere
since the 1800s.
23. Besides carbon dioxide, what are some other gases that may be contributing to the
greenhouse effect?
24. Explain why carbon dioxide levels seem to increase in areas during the winter but decrease in
those same areas during the summer.