Suggest why the presence of the sieve plate is often cited as evidence against the pressure-flow model for phloem transport

I think this is because the role of sieve plates is unclear, the mass flow would improve without them and therefore their presence goes against the mass flow theory. The mass flow hypothesis explains translocation which is the movement of sugars and amino acids in solution from a high pressure region to a low pressure region through the phloem sieve tubes. 

The answer would be c, white eyes are homozygous recessive. in the early 1900s, morgan conducted several experiments with vinegar  flies (drosophila). one  sample revealed an anomaly: a  white-eyed, single male fly. he attempted to breed this fly with the typical red-eyed females. the offspring were all red-eyed. using flies from this new generation (brother-sister pairs)  produced some red-eyed and a few white-eyed flies. the white-eyed were all male. in later experiments, he was able to produce white-eyed females. this proved that white eyes are not lethal to either sex (ruling out a and b). since the percentage of white eyes to red eyes is so low, white eyes are not a dominant trait. it would be a recessive trait. 

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