Green microalgae and diatoms are responsible for roughly half of the oxygen we breathe every day.
They were also the first organisms in history to start producing oxygen, long before the first plants developed. In doing so, they laid the basis for earth’s atmosphere, which in turn allowed other organisms to evolve into the rich fauna and flora we know today.
The evolution of chloroplasts, the specialised organelles responsible for photosynthesis in plants and microalgae, is closely linked to cyanobacteria. According to the 'endosymbiotic theory', chloroplasts descended from ancient cyanobacteria (which were the first photosynthetic organisms), which were engulfed by early eukaryotic cells in a symbiotic relationship.
Over time, these cyanobacteria became integrated into host cells, giving them the ability to perform photosynthesis independently, paving the way for the evolution of plants and algae. This mutualistic relationship was incredibly advantageous and led to the development of multicellular organisms with the capacity for more complex life cycles and diverse ecological niches.
Achnanthes cf. subsessilis (DCG 0322)
Diatoms are amongst the most successful photosynthetic organisms on the planet, being in charge for about 40% of the world's annual primary productivity. This remarkable efficiency is thanks to the diatom’s glass cell wall, also known as a frustule. The frustule consists of many layers which are lined with pores of different sizes in each layer. Together these interact as a biological photonic structure: a structure with the ability to change its refractive index to manipulate the light. In the case of diatoms, even a small amount of light can be transferred evenly throughout the entire cell. As such, all incident light can be transferred to all chloroplasts due to the conduction through the frustule. This leads to a more efficient photosynthesis compared to other green algae.