Life of Plants (part 1)
Cyanobacterias, endosymbiosis, alga and diatoms
The role of the plants began on planet earth 2 billion years ago, creating a collaboration between the unicellular forms of the time, especially by cyanobacteria (also known as blue-green algae), where mutually beneficial relationships were created between them or with bacteria that allowed the formation of chloroplasts, the organelle that allows the development of photosynthesis, the process by which plants convert the dioxide present in the atmosphere into sugars (which provide energy) through the use of sunlight. Thanks to the development of photosynthesis, these organisms (cyanobacteria) became the main source of the rapid increase in oxygen levels in the atmosphere, today they continue to provide more than half of the earth’s oxygen. The evidence is based in the form of microfossils and stromatolites.
Cyanobacteria are prokaryotic organisms, which are simple, unicellular organisms, lacking a nucleus to concentrate their genetic material and other structures. The first colonies of microfossil bacteria and the first stromatolites appear during the Archean, 3 billion years ago, and bacterial life on earth dominated for more than 1 billion years.
There is convincing evidence of shared features suggesting that chloroplasts were a type of free-living cyanobacteria, as is the case with the photosynthetic pigments of cyanobacteria, which are the same as those found in chloroplasts of algae and algae land plants; microstructures found in chloroplasts, which are similar to those found in modern cyanobacteria; Chloroplasts are almost the size of cyanobacteria and also reproduce in the same way. These similarities point to a common ancestry between cyanobacteria and chloroplasts, a link explained in the endosymbiosis theory proposed by Lynn Margulis in the 1960s.
Two billion years ago, the first eukaryotic cells appeared as a result of the endosymbiosis process, composed of internal structures such as chloroplasts or mitochondria.
Simple modern plant-like algae consist of a number of organisms with very different structures, but identical photosynthetic pigments. This is because the various types of algae evolved when a number of different host organisms formed symbiotic unions with the same photosynthetic prokaryotic cells. These mixed origins have caused algae to be extraordinarily diverse, from single-celled diatoms, to marine algae (green, red, and brown), from sea lettuce to Laminaria digitata and giant brown algae, to freshwater algae like Chara. It should be noted that the first red and brown algae appeared 1.2 billion years ago, organisms similar to plants, unicellular or concentrations of similar cells, more complex than cyanobacteria.
Diatoms are common freshwater marine algae, they may have been around for billions of years. Living diatoms contain chloroplasts and carry out photosynthesis. They are highly diversified, with 200,000 different species.
Considered (normally) as unicellular algae, diatoms are divided into two large groups according to their shape: diatoms of radial symmetry in which their parts radiate from a central point, on the other hand, diatoms of bilateral symmetry in the that the left and right parts are mirror images of each other. The cell walls of diatoms are made of opaline silica through which, through small perforations, they absorb nutrients and excrete waste (each species has a unique configuration of holes). The importance of diatoms is due to the fact that their presence and evolutionary forms are used to determine nutrients, temperatures and other changes in marine and freshwater environments over millions of years.
The information in this story was taken from the work of Parker, S. (2016). “Evolution. The Whole Story”, from pages 56, 57, 58 and 59.