Flexi Says: The first organisms to photosynthesize were cyanobacteria. These organisms may have been around as far back as 3.5 billion years. Cyanobacteria are still alive today. Now they are called blue-green algae. They are common in lakes and seas, and they account for 20% to 30% of photosynthesis today.
Scientists think that red and green algae evolved from endosymbiotic relationships with cyanobacteria. Their chloroplasts have two membranes because the cell membranes of the cyanobacteria became additional plasma membranes of the chloroplasts.