Final answer:
Algae developed chloroplasts through primary endosymbiosis by engulfing cyanobacteria, and variations such as secondary endosymbiosis gave rise to different algal groups. Gene mutations played a role in the diversity of photosynthetic pigments, such as chlorophylls and carotenoids.
Step-by-step explanation:
Algae developed their chloroplasts through a process known as endosymbiosis, where ancestral algae engulfed different photosynthetic bacteria. This event is recognized as the primary acquisition of chloroplasts. These primary chloroplasts have two membranes which correspond to the inner and outer membranes of the original cyanobacteria and the plasma membrane of the engulfing eukaryotic cell. Additionally, the chloroplasts found in later evolved algal lineages were often the result of secondary endosymbiosis, where another eukaryotic cell engulfed an algae that already had primary chloroplasts, leaving these new chloroplasts with three or four membranes.
Different pigments in various algal groups, such as chlorophylls and carotenoids, arose due to the presence of accessory pigments and types of chlorophyll molecules beyond chlorophyll a, which is common across all photosynthetic organisms. Gene mutations over time contributed to the diversity of these pigments. The carotenoids and varying chlorophylls allow algae to capture light energy for photosynthesis effectively. The chloroplasts of red and green algae contain DNA sequences similar to cyanobacteria, supporting the endosymbiotic theory and emphasizing the shared evolutionary history between these organisms.