“When a cell ‘dies’ is a hard question,” he says, “Some cells stay alive inside others for a long time, even after partially being digested.” There are single-celled creatures that feed on algae but leave the parts that turn sunshine into food—the chloroplast—alive and working for long periods.

Interesting - that reminds me of what I was taught back in high school/university, which is that we suspect that mitochondria/chloroplasts were actually the result of a very simple organism "consuming" another bacteria and it ends up surviving and incorporating over time. This is very simplified, but a quick google says this is called the endosymbiosis theory.