Final answer:
Bacteria grown on LB agar with ampicillin and a substance that changes color when exposed to the enzyme produced by the lacZ gene can be used to identify bacteria with a recombinant plasmid that contains a foreign DNA insert.
Step-by-step explanation:
To find the bacteria with the recombinant plasmid, the bacteria are grown on a plate with the antibiotic ampicillin and a substance that changes color when exposed to the enzyme produced by the lacZ gene. The ampicillin will kill any bacteria that did not take up a plasmid. The color of the substance will not change when the gene for lacZ contains the foreign DNA insert. These are the bacteria with the recombinant plasmid that we want to grow.