What structure, in the human body, performs similar function as sieve tube?

this is true, assuming that the allele is completely recessive and incomplete dominance is not a factor.

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.