A culture of E. coli is grown on minimal medium plates supplemented with either tryptophan, histidine, or lysine. The resulting colonies are replica plated to three minimal medium plates containing no supplements. The next day, colonies grow on the minimal medium replica plated from the histidine and lysine plates, but colonies do not grow on the tryptophan replica plate. This indicates that the E. coli strain is a.

tryptophan auxotroph

Explanation:

Tryptophan is known to be a crystaline essential amino acid that is widely distributed or mostly found in proteins.

An auxotroph is an organism that is not able to synthesize a compound needed  for its growth.

In this case, E. coli is described as a tryptophan auxotroph because it was unable to synthesize or make use of the tryptophan vy growing in the plate containing it.

increase soil erosion                                             reduce soil erosion

cattle grazing                                                         hydroseeding

deforestation                                                         contour plowing

                                                                                planting vegetation

plant roots basically hold the top soil

together and stop soil erosion because

in such situation top soil is not removed

during flood but cattle grazing causes

soil erosion because cattle consume the

grasses and herbs and top soil is exposed.

same situation occurs because of

deforestation, the trees and plants are cut

down to expose top soil which causes soil

erosion