This story takes place a long, long time ago and is about the origins of our modern life. This is not just a scientific theory, but a legend that spans billions of years of life – it is the endosymbiosis hypothesis.
Imagine that in those ancient times, the ocean was vast, deep, and full of all kinds of strange creatures. The sun has just risen in the sky, and its rays are shining on the sparkling sea, and in this ocean full of life, some tiny life forms are performing a miracle of life.
The protagonist of this story is a single-celled microorganism called prokaryotes, which have a simple structure and no complex organelles. These microbes float freely in the pristine oceans, some are good at photosynthesis, and some like to devour the material around them.
One day, a microorganism that resembles a modern phagocytic protozoa, let's call it a "food bully", accidentally swallowed a cyanobacteria that excels at photosynthesis. These cyanobacteria, which we call "blue boys", have the wonderful ability to use sunlight to make food. Normally, "Eater" would digest the food he caught, but this time, for some mysterious reason, "Blue Boy" was not completely digested.
The Blue Boy lived in the body of the "Eater" and began to reproduce. Over time, the "food tyrant" found that not only did he not feel unwell because of the "Blue Boy" residence, but was able to use the nutrients produced by the "Blue Boy" to maintain his own survival. Thus, a wonderful symbiotic relationship was established.
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As the long river of evolution flows slowly, this symbiotic relationship becomes more and more intimate. Eventually, the Blue Boy became a permanent part of the Eater's body, which we call chloroplasts. Chloroplasts retain the ability of cyanobacteria to photosynthesize, giving host cells the ability to produce energy from sunlight. This is the origin of plants and algae having photosynthesis.
A lot has happened along the way. For example, the "blue boys" who were originally independent had to give up a lot of autonomy, and many of their genes were integrated into the genome of the host cell. This also makes the "eater" more complicated, and it gradually develops the characteristics of eukaryotes, such as having a real nucleus and other complex organelles.
Not only that, but this story also tells some other wonderful plots. For example, mitochondria, another important organelle we now use to produce energy, are also said to have evolved from an ancient aerobic bacterium through a similar endosymbiotic event.
The endosymbiosis hypothesis explains why the cells of plants, algae, and certain protists have unique structures that look like separate bacteria, but are an integral part of the cell. This hypothesis provides a framework for understanding the diversity and complexity of life.
Now, when you see a green leaf or a bunch of seaweed, you can imagine that those green chloroplasts were once free cyanobacteria, and the story between them and the host cell has been going on for billions of years. In this process, countless lives were born, evolved, and flourished, constituting the colorful biological world we see today.
So, the next time you're walking in the sun, think about this amazing story of how tiny chloroplasts support the functioning of entire ecosystems through photosynthesis. This is not only a scientific hypothesis about the origin of life, but also a vivid story of symbiosis and cooperation, as well as the continuous adaptation and evolution of life.