Final answer:
The statement that chloroplasts are descendants of cyanobacteria is true, originating from a symbiotic relationship that occurred billions of years ago, known as primary endosymbiosis.
Step-by-step explanation:
Through a process known as primary endosymbiosis, an ancestral eukaryotic cell engulfed cyanobacteria which eventually led to the evolution of modern-day chloroplasts. This relationship has allowed chloroplasts to retain characteristics reminiscent of their bacterial ancestors, such as thylakoids, circular DNA, and ribosomes.
The endosymbiotic theory, first proposed by Lynn Margulis, suggests that organelles like chloroplasts originated from free-living bacteria that were taken inside a host cell. Over time, these internalized bacteria became integral to their host cells, losing the ability to live independently and becoming the organelles we see today.
This evolutionary step is crucial for photosynthesis in eukaryotes, with most photosynthetic eukaryotes descended from a common ancestor that experienced this symbiotic event. Therefore, the statement is true.