Final answer:
The family of Henrietta Lacks found out about the existence of cell culture from their mother's cells, which were taken without her consent. Her cells, known as HeLa cells, are immortal and have been used in various experiments and treatments.
Step-by-step explanation:
The family of Henrietta Lacks found out about the existence of cell culture from their mother when they learned that her cells had been taken and used for medical research without her consent. They discovered that her cells, known as HeLa cells, were immortal and could reproduce rapidly and indefinitely. Henrietta Lacks' cells have been widely used in experiments and treatments, including the development of the polio vaccine.