Chloroplasts ended up in producers' cells through a process called endosymbiosis, where an early eukaryotic cell engulfed a photosynthetic cyanobacterium. This cyanobacterium then became a permanent resident inside the host cell, evolving into the chloroplast organelle found in plants and algae today
. Key points about this process include:
- The engulfed cyanobacterium was capable of photosynthesis, producing energy that benefited the host cell
- This event likely occurred over 2 billion years ago, with the chloroplast lineage splitting from its closest cyanobacterial ancestor around that time
- Over evolutionary time, many genes from the cyanobacterium were transferred to the host cell’s nucleus, reducing the chloroplast genome and integrating its function tightly with the host cell
- Chloroplasts retain some bacterial features, such as their own DNA and the ability to reproduce independently within the cell, supporting their origin as once free-living bacteria
- This symbiotic relationship allowed the host cells to perform photosynthesis, turning them into producers capable of converting sunlight into chemical energy
Thus, chloroplasts are descendants of ancient cyanobacteria that became endosymbionts inside early eukaryotic cells, leading to the photosynthetic cells we see in plants and algae today. This endosymbiotic origin is the foundation of how chloroplasts came to reside in producer cells.
