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III. Prepositions

Fill in the correct preposition for each blank space.

1. Herein is the first basic principle ecosystem sustainability:

sustainability, ecosystems dispose wastes and replen­ ish nutrients recycling all elements.

2. This principle is harmony the Law Conser­ vation Matter.

•>• Wfe can see this even more clearly focusing the path­ ways three key elements: carbon, phosphorus, and nitrogen.

4- It is convenient to start the carbon cycle the "reservoir"

carbon dioxide molecules present the air and dis­ solved water.

60

Unit Five

Ecosystems: How They Work

61

5. Through food chains, the carbon atoms then move and be­ come part the tissues all the other organisms

the ecosystem.

6. However, it is unlikely that a particular carbon atom will be passed

many organisms any one cycle because each

step there is a considerable chance that the consumer will break the organic molecule cell respiration.

                  1. As this occurs, the carbon atoms are released back the envi­ronment molecules carbon dioxide, thus complet­ing one cycle, but course ready to start another.

                  1. Phosphate dissolves water but does not enter air.

                  1. The phosphate may then be reabsorbed plants to start an­other cycle.

10. No matter carbon dioxide is released, it will mix and

maintain the concentration carbon dioxide the air.

                  1. A very serious case humans interfering the phospho­rus cycle is seen the cutting tropical rainforests.

                  1. This type of ecosystem is supported a virtually 100 percent

efficient recycling nutrients.

13. Meanwhile, phosphorus is replaced croplands min­ ing phosphate rock a process that will ultimately result

depletion.

14. Fixed organic nitrogen is passed the legumes other

organisms the ecosystem food chains.

IV. DEFINITE/INDEFINITE ARTICLES

Use a/an or the where needed. If no article is needed, write an A" in the blank space.

However, it is unlikely that particular carbon atom

will be passed through many organisms on any one cy­ cle because at each step there is considerable chance that .

consumer will break down organic molecule in cell res­ piration. As this occurs, carbon atoms are released back to .

environment in molecules of carbon dioxide, thus com­ pleting one cycle, but of course ready to start another. Like­ wise, burning organic material returns carbon atoms

locked up in material to air in carbon dioxide

molecules. No two successive cycles of particular carbon atom

are likely to be same. Nor are two cycles likely to be

within same ecosystem because in atmosphere

wind will carry them around globe.