11. The transformation of nitrates to gaseous nitrogen is accomplished by microorganisms in a series of biochemical reactions. The process is known as

A. nitrification
B. denitrification
C. nitrogen fixation
D. ammonification

12. Nitrogen fixation refers to the direct conversion of atmospheric nitrogen gas into

A. ammonia
B. glucose
C. ATP
D. nitrate

13. The diagnostic enzyme for denitrification is

A. nitrate reductase
B. nitrate oxidase
C. nitro oxidoreductase
D. none of these

14. A heterocyst is

A. a type of spore
B. a terminally differentiated cell that fixes nitrogen
C. the progenitor of cyanobacterial vegetative cells
D. a cell that carries out oxygenic photosynthesis

15. The groups of symbiotic bacteria, which have the ability to fix nitrogen

A. derive their food and minerals from the legume, and in turn they supply the legume with some or all of its nitrogen
B. grow together for a mutual benefit is called symbiosis and so these bacteria are called symbiotic nitrogenfixing bacteria
C. these bacteria are from the genus, Rhizobium
D. all of the above