Down Syndrome is a genetic disorder in humans caused by having three copies of chromosome 21 In their cells how could a person with this disorder
have gotten an extra copy of this chromosome?

A. Replication of chromosome 21 after meiosis
B. Nondisjunction of chromosome 21 during meiosis
C. Crossing over of chromosome 21 with other chromosomes
D. Recombination of chromosome 21 with other chromosomes

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.

when it is at an intermediate population density

colors do exist. the color of the sky is actually violet; humans percieve the color of the sky as blue.