Final answer:
To determine if a cell took up the plasmid, a selective marker like an antibiotic resistance gene is used. If the cell took up the plasmid, it will be able to grow on a medium containing the specific antibiotic.
Step-by-step explanation:
The presence of the plasmid in the cell can be determined using a selective marker, such as an antibiotic resistance gene. Plasmids contain a resistance gene for a specific antibiotic, so if a cell takes up the plasmid, it will be able to grow on a medium containing that antibiotic. In the case of ampicillin, for example, cells that have taken up the plasmid will grow on media with ampicillin, while cells that have not taken up the plasmid will not grow.