Bacteria didn't directly become plants. Instead, plants evolved through a process called endosymbiosis, where a eukaryotic cell engulfed a cyanobacterium.
The Endosymbiotic Theory and Plant Evolution
The modern understanding of plant evolution hinges on the endosymbiotic theory. This theory posits that certain organelles within eukaryotic cells, specifically chloroplasts in plants and algae, originated as free-living prokaryotic organisms (bacteria).
Key Steps in the Process:
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Engulfment: A eukaryotic cell (a cell with a nucleus) engulfed a cyanobacterium, a type of bacteria capable of photosynthesis.
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Symbiosis: Instead of digesting the cyanobacterium, the eukaryotic cell formed a symbiotic relationship with it.
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Chloroplast Formation: Over time, the cyanobacterium evolved into a chloroplast, the organelle responsible for photosynthesis in plant cells. The cyanobacterium effectively became an "internal solar power plant."
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Inheritance: This symbiotic relationship was passed down through generations, ultimately leading to the evolution of algae and, eventually, land plants.
Importance of Cyanobacteria
Cyanobacteria are crucial to this process because they are photosynthetic, meaning they can convert sunlight into energy. By incorporating cyanobacteria, eukaryotic cells gained the ability to perform photosynthesis, a key characteristic of plants.
Examples
- All plants and algae owe their photosynthetic capabilities to this single endosymbiotic event involving a cyanobacterium. From giant redwood trees to microscopic diatoms, their existence is rooted in this ancient symbiosis.
Summary
The evolution of plants involved a critical step: a eukaryotic cell engulfed a cyanobacterium and transformed it into a chloroplast through endosymbiosis. This event enabled the eukaryotic cell, and its descendants, to perform photosynthesis, a defining characteristic of plants.
