Final answer:
The source of freshwater harmful algal blooms and chloroplasts in eukaryotic cells is believed to be cyanobacteria, specifically derived from photosynthetic bacterial endosymbionts. The endosymbiotic theory explains the evolution of chloroplasts and mitochondria in eukaryotic cells as a result of ancient symbiotic relationships. Cyanobacteria, also known as blue-green algae, obtain their energy through photosynthesis and are found in various environments.
Step-by-step explanation:
In the endosymbiont theory, cyanobacteria are identified as the source of freshwater harmful algal blooms, nitrogen fixation, and the source of chloroplasts in eukaryotic cells. Cyanobacteria, also known as blue-green algae, obtain their energy through photosynthesis and are found in terrestrial, marine, and freshwater environments.
Based on the endosymbiotic hypothesis, chloroplasts are thought to have originated from ancestral photosynthetic bacteria, specifically cyanobacteria, that were living in a symbiotic relationship within eukaryotic cells. This theory suggests that the evolution of eukaryotic cells involved the incorporation of cyanobacterial endosymbionts, which eventually formed chloroplasts.
The endosymbiotic theory is widely accepted and supported by evidence such as chloroplasts and mitochondria having their own DNA and ribosomes, similar size and features to bacteria, and their ability to reproduce independently. This theory proposes that organelles like mitochondria and chloroplasts are the result of ancient symbiotic relationships between ancestral host cells and bacteria.