Demographers developed a hypothesis to explain the changes to the populations of countries over time. This hypothesis describes a demographic transition, in which countries change from a combination of high birthrates and high death rates to low birthrates and low death rates. The changes of the demographic transition are summarized in the graph. Birth rate and death rate are plotted against time. At first (Stage 1) both rates are high. Then in Stage 2, birth rate remains high while death rate decreases. In Stage 3, birth rate decreases to match the low death rate.

Describe the changes that a country undergoes as it passes through the three stages of the demographic transition. Use the United States as an example.

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.

the answer is lactic acid from anaerobic respiration. the acid in lactic acid is what creates sore and burning muscles. if you think about how acid burns that will give you a clue for questions like this.

answer; motor (efferent)neurons;