Why is DNA replication called semiconservative?
DNA replication is called semiconservative because an existing DNA strand is used to create a new strand.
DNA is a double stranded molecule. When DNA is copied the two strand of DNA (old strands) separate and new nucleotides match up with the two separated strands.
This process creates two identical double stranded DNA molecules are formed. Each DNA molecule contains one strand of the original DNA molecule and one newly synthesized (made) strand.
You can watch how this happens in the video below.
Hope this helps!