Final answer:
The semiconservative model of DNA replication means that each new DNA molecule consists of one old (parental) and one new strand, a discovery confirmed by Meselson and Stahl.
Step-by-step explanation:
The term semiconservative refers to the method by which DNA is replicated. During DNA replication, each of the original DNA strands, or parental strands, serves as a template for a new strand, resulting in two DNA molecules that each contain one original and one new strand. Thus, half of the parent DNA molecule is conserved in each daughter molecule, which justifies the term 'semiconservative'. This important discovery was made by Matthew Meselson and Franklin Stahl in 1958, through their famous experiment utilizing densities of different nitrogen isotopes to demonstrate that each new DNA molecule consisted of one old and one new DNA strand.
The elucidation of the double helix structure by James Watson and Francis Crick in 1953 provided the clue to the semi-conservative mechanism that was later experimentally validated by Meselson and Stahl. The alternative models that they disproved were the conservative model, where the original DNA molecule might have remained intact and generated a completely new molecule, and the dispersive model, where each strand would be a mix of old and new DNA.