For each predator-prey system: a. determine which of the variables, x or y, represents the prey population and which represents the predator population b. is the growth of the prey restricted just by the predators or by other factors as well? do the predators feed only on the prey or do they have additional food sources? explain.

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.