Chapter 13 Study Questions

  1. What is the source of NH4+ in plant cells? Explain how NH4+ can be toxic to cells. How is this toxicity avoided?


  2. Textbook Reference: Nitrogen in the Environment, pp. 355–356; Ammonium Assimilation, p. 358

  3. Nitrogen is taken up as NO3– by roots and converted first into NO2–, and then to NH4+, and the amide nitrogen of glutamine. What are the main enzymatic steps of this assimilatory process? How much ATP is consumed, and in which steps?


  4. Textbook Reference: Nitrate Assimilation, pp. 356–360

  5. Explain the symbiotic association between higher plants and nitrogen-fixing bacteria, and provide an example of this type of association.


  6. Textbook Reference: Biological Nitrogen Fixation, pp. 360–367

  7. What are the Nod factors? Describe the genes involved in their production.


  8. Textbook Reference: Biological Nitrogen Fixation, pp. 364–365

  9. What are the main enzymatic steps mediating the assimilation of sulfate? What is sulfate activation? Why is it necessary for the assimilation of sulfate into organic compounds?


  10. Textbook Reference: Sulfur Assimilation, pp. 367–369