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Homework answers / question archive / 12
12.
A. Amount of NO_3 -1 (nitrate ion) taken up and used by plants.
B. Amount of N_2 (molecular nitrogen) taken up and used by plants.
13.
A. Net 1 degree production of grasses being subjected to moderate-intensity grazing.
B. Net 1 degree production of grasses being subjected to high-intensity grazing.
14.
A. Rate of nutrient cycling in detritus containing lots of lignin and little nitrogen.
B. Rate of nutrient cycling in detritus containing little lignin and lots of nitrogen.
15.
A. Amount of energy "captured" during gross 1 degree production in an ecosystem.
B. Amount of this captured energy that is eventually "lost" as heat from the same ecosystem.
Questions 16-20: Write the letter of the one most correct answer in the blank space.
16. Ecological efficiency in an ecosystem has an overall average of about:
A. 90%
B. 80%
C. 40%
D. 20%
E. 10%
17. Growth and reproduction of the decomposers in an ecosystem is part of:
A. gross 1 degree production
B. net 1 degree production
C. gross 2 degree production
D. net 2 degree production
18. The typical number of links in a grazing food chain is:
A. 1-2
B. 3-4
C. 5-6
D. 7-8
19. Which of the following would be a correct, direct sequence for the movement of nitrogen within the nitrogen cycle?
A. atmosphere --> produces --> atmosphere
B. atmosphere --> consumers --> decomposers
C. producers --> consumers --> decomposers
D. decomposers --> consumers --> producers
20. What percentage of nitrogen fixation is done by organisms?
A. 90%
B. 80%
C. 40%
D. 20%
E. 10%
Questions 21-27: If the statement is true, write a "T" in the blank space. If the statement is false, write an "F" in the blank space an correct the underlined part so that the statement is true.
21. The 2nd law of thermodynamics indicates that when energy is transformed some of it can be used for biosynthesis and some of it is converted to unusable heat.
22. Pollutants become less concentrated as they are passed along a food chain.
Answers:
12. A Plants do not use atmospheric nitrogen (N2) directly. Thus it needs to be converted to NO3 - (nitrate) for use by the plants.
13. A. Grazing stimulates 4-45% greater net primary production, the stimulation being higher at lightly and moderately grazed sites. Moderate grazing leads to a lesser removal of vegetation from the site as compared to high intensity grazing; hence the net primary productivity is higher in moderately grazed sites.
14. A. Detritus organisms feed on waste organic matter. Thus they would better feed on lots of lignin with less nitrogen.
15. A. Amount of energy captured at the primary level is more than the amount of energy lost from this energy at the next trophic level. 10% of energy is captured and 90% of this 10% is lost at next trophic level.
16. E Only 10% of the energy is passed to next trophic level.
17. C Decomposers have a prime role in the cycling of nutrients thus leading to gross secondary production.
18. B Grazing food chain comprises solar energy, plants, herbivores and finally carnivores.
19. C
20. A
21. True The energy is not completely used, 10% is stored in tissue biomass and 90% is removed in form of heat.
22. False. Pollutants become more concentrated as they are passed along the food chain. This is known as Biomagnification.
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