Answer
cyanobacteria
Work Step by Step
Like land plants and red algae, green algae have chloroplasts that evolved from cyanobacteria, single-celled organisms that make their own food through the process of photosynthesis. This transformation from cyanobacteria into chloroplasts was the result of endosymbiosis, the process by which a single-celled organism lives inside another single-celled organism, and the two organisms become dependent on one another for survival.
