The Nitrogen Cycle - AP Environmental Science

1. Name one impact of industrial nitrogen fixation.

   Increased crop yields. Synthetic fertilizers dramatically boost agricultural productivity.

2. What is the main function of nitrogen-fixing bacteria in root nodules?

   Convert $N_2$ to ammonia. Use nitrogenase to break triple bonds in atmospheric nitrogen.

3. What is the main reservoir of nitrogen in the nitrogen cycle?

   The atmosphere. Contains 78% of Earth's nitrogen in unreactive $N_2$ form.

4. Which process involves the conversion of nitrates back to nitrogen gas?

   Denitrification. Anaerobic bacteria reduce nitrates, completing the nitrogen cycle.

5. Identify one environmental issue caused by excess nitrogen from agriculture.

   Water pollution. Runoff causes eutrophication and groundwater contamination.

6. What is the primary impact of nitrogen oxides in the atmosphere?

   Acid rain formation. Nitrogen oxides react with water to form nitric acid.

7. What is the chemical formula for nitrous oxide?

   $N_2O$. Two nitrogen atoms bonded to one oxygen atom.

8. What is the main form of nitrogen found in fertilizers?

   Ammonium nitrate. Common synthetic fertilizer providing readily available nitrogen.

9. What is the impact of nitrogen on the atmosphere when released as a pollutant?

   Contributes to smog. Nitrogen oxides contribute to photochemical air pollution.

10. Identify the nitrogen compound that contributes to greenhouse gas emissions.

    Nitrous oxide ($N_2O$). Potent greenhouse gas with 300 times warming potential of $CO_2$.

11. What process converts organic nitrogen in dead organisms to ammonia?

    Ammonification. Decomposition releases ammonia from organic nitrogen compounds.

12. Identify the process that converts nitrates to nitrogen gas in waterlogged soils.

    Denitrification. Occurs in oxygen-poor conditions like wetlands and sediments.

13. Which process in the nitrogen cycle is anaerobic?

    Denitrification. Requires oxygen-free environment for bacteria to function.

14. What is the process called when plants uptake nitrates from the soil?

    Assimilation. Plants absorb nitrogen compounds through their root systems.

15. Identify the key enzyme used by bacteria to fix nitrogen.

    Nitrogenase. Catalyzes the energy-intensive conversion of $N_2$ to $NH_3$.

16. State the role of legumes in the nitrogen cycle.

    Host nitrogen-fixing bacteria. Provide shelter and nutrients for nitrogen-fixing bacteria.

17. Identify the nitrogen compound that plants primarily absorb from soil.

    Nitrates ($NO_3^-$). Highly soluble and mobile form preferred by most plants.

18. Identify the process that bacteria use to convert ammonia into nitrite.

    Nitrification. First step in nitrification where ammonia becomes nitrite.

19. Which gas is released during the process of denitrification?

    Nitrogen gas ($N_2$). Returns nitrogen to atmosphere, completing the cycle.

20. Identify the product when nitrogen gas is fixed by bacteria.

    Ammonia ($NH_3$). Direct product of nitrogen fixation by bacterial nitrogenase.

21. Name the process by which ammonia is converted to nitrites and nitrates.

    Nitrification. Two-step oxidation process performed by soil bacteria.

22. What is the main consequence of excess nitrogen in aquatic systems?

    Eutrophication. Excess nitrogen causes algal blooms and oxygen depletion.

23. What is the final product of the denitrification process?

    Nitrogen gas ($N_2$). Completes the nitrogen cycle by returning to atmosphere.

24. Which soil bacteria convert ammonia into nitrites?

    Nitrifying bacteria. First step in two-stage nitrification process.

25. What organisms primarily perform nitrogen fixation?

    Nitrogen-fixing bacteria. Contain nitrogenase enzyme that converts $N_2$ to $NH_3$.

26. Identify the process that converts atmospheric nitrogen into ammonia.

    Nitrogen fixation. Breaks the strong triple bond in $N_2$ to create bioavailable forms.

27. Which organism type is crucial for the nitrogen cycle in aquatic systems?

    Cyanobacteria. Blue-green algae that fix nitrogen in marine environments.

28. Which process releases ammonium ions from organic matter?

    Ammonification. Bacterial decomposition converts organic nitrogen to inorganic forms.

29. What is the chemical formula for ammonia?

    $NH_3$. Product of nitrogen fixation with one nitrogen and three hydrogens.

30. Identify the form of nitrogen that plants can directly absorb and use.

    Nitrates ($NO_3^-$). Most oxidized and soluble form readily absorbed by plant roots.

31. Name the symbiotic relationship between legumes and nitrogen-fixing bacteria.

    Mutualism. Both organisms benefit from the nitrogen-fixing relationship.

32. State the role of lightning in the nitrogen cycle.

    Nitrogen fixation. High energy electrical discharge breaks $N_2$ bonds naturally.

33. What is the chemical formula for nitrite?

    $NO_2^-$. Intermediate form with one nitrogen and two oxygen atoms.

34. What is the role of decomposers in the nitrogen cycle?

    Ammonification. Break down proteins and nucleic acids, releasing ammonia.

35. What type of bacteria is responsible for converting nitrites to nitrates?

    Nitrifying bacteria. Complete the nitrification process by oxidizing nitrites.

36. Which human activity contributes significantly to nitrogen fixation?

    Fertilizer production. Industrial Haber-Bosch process creates synthetic nitrogen compounds.

37. What is the first step in the nitrogen cycle that involves atmospheric nitrogen?

    Nitrogen fixation. Converts inert atmospheric $N_2$ into reactive compounds.

38. Name the process that involves the conversion of ammonium to nitrite.

    Nitrification. First oxidation step in the two-stage nitrification process.

39. State the chemical formula for nitrate.

    $NO_3^-$. One nitrogen atom with three oxygen atoms and negative charge.

40. State the effect of nitrogen on plant growth.

    Promotes growth. Essential nutrient for protein synthesis and chlorophyll production.

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