[Campbell Biology P.866] The passage describes an indirect benefit of mutualistic nitrogen f... | Practice Question

The passage describes an indirect benefit of mutualistic nitrogen fixation for rice farmers. Which of the following best explains how Azolla contributes to this benefit?

  • A: Azolla directly fixes nitrogen from the atmosphere into the rice plant.
  • B: Azolla forms root nodules with rice plants to facilitate nitrogen transfer.
  • C: Azolla hosts nitrogen-fixing cyanobacteria, and its decomposition enriches the paddy with nitrogen.
  • D: Ducks eat Azolla, directly fertilizing the rice paddy with their droppings, which contain fixed nitrogen.

Explanation

The passage states that rice benefits indirectly from mutualistic nitrogen fixation because Azolla, a free-floating aquatic fern, hosts mutualistic cyanobacteria that fix nitrogen. The growing rice shades and kills the Azolla, and the decomposition of this nitrogen-rich organic material increases the rice paddy's fertility.