Explain why DNA replication is semi-conservative

When DNA is replicated, the original DNA double helix is separated into two strands. Each strand is used as a template for complimentary free nucleotides to bind to and create new complimentary DNA strand. This results in two DNA double helices, each one containing one old strand and a new strand. As the one of the two original DNA strands are conserved with each replication, DNA replication is said to be semi-conservative.