~~8. a horticulturist has a purple plant and a white plant. the horticulturist knows that purple is dominant over white. when they are bred, all of the resulting offspring are purple. what is the most likely genotype of the parent or original purple plant

The purple allele(P) - dominant
white allele (p) - recessive 
for the recessive allele to be expressed, both alleles should be recessive. The white plant therefore should have both p alleles. Genotype of white plant is pp.

the other parent is a purple plant. For the dominant allele to be expressed, at least one of the alleles should be P. Therefore genotype of the purple plant should have one P allele. the other allele needs to be determined.

For all the offspring, they receive one p allele from the white plant, since they are purple the other allele should be P.Genotypes of offspring should be Pp. For all the offspring to receive P from purple plant then purple plant should be homozygous PP, to give only P alleles.

Therefore genotype of parent purple plant is PP. 

Ithink that b is correct but just in case wait to see if someone else answers