Which is an example of a response to a stimulus
a. loss of water from the body as a result of excess sweating
b. the thick fur on an animal to protect it from cold weather
c. an increasing heart rate when blood oxygen levels drop
d. the presence of allergens in the air

heat a spark and oxygen

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.