**1. Evolution of photosynthetic systems**

Photoautotrophy is a complex process that some eukaryotic organisms can carry out. Some bacteria, algae, and plants share this capacity to transform light and carbon dioxide into biomass. Photosynthesis requires chlorophyll and other accessory pigments. There are three evolution lines that are recognized according to the types of pigments present in chloroplasts (specialized organelle where photosynthesis is performed) of these organisms (**Figure 1**).

From the above figure,


It is believed that a second endosymbiosis event occurred and can explain the presence of additional membranes in chloroplasts. The members of the secondary red endosymbiotic event constitute a very diverse group of organisms, and the most important from the pharmaceutical point of view are diatoms (Heterokonta) and the dinoflagellate (Alveolata) [2].

In this sense, reaction centers of photosystems I and II (PSI and PSII) of photosynthetic prokaryotes have similar elements and homologous structures, and therefore it is believed that photosynthetic reaction centers have evolved only once. On the contrary, light harvesting complexes are very different between taxa, share no sequence, and have very little structural similarity (**Figure 2**). This indicates that light harvesting complexes of higher plants, cyanobacteria, purple bacteria, and green sulfur bacteria evolved independently from each other [6, 7]. This means that genes of the antenna may have duplicated and

Introductory Chapter: Evolution of Photosynthesis http://dx.doi.org/10.5772/intechopen.80230 5

**Figure 2.** Representation of the reaction center and antenna structures of different taxa of photosynthetic organisms. Reaction centers have similar structures. While the organization of light harvesting antenna complexes relative to the photosynthetic membrane have very different structure. Examples shown are representative of: a, Higher plants and

green algae. b, Cyanobacteria and red algae. c, Cryptophytes (Image from Scholes et al., 2011).

**Figure 1.** Schematic representation of the primary and secondary endosymbiosis events that gave origin to mayor taxonomic division of organisms that perform oxygenic photosynthesis. All terrestrial plants have their origin from a green primary endosymbiosis event. Most of the aquatic photoautotroph organisms are secondary endosymbionts with red plastids lineage [1].

What are the differences between algae and land plants? Algae are thallophyte, that means they lack of roots, leafs, stomas, and complex reproductive organs [3]. Algae do not form embryos, all reproductive structures are potentially fertile, and protective sterile cells are absent. Development of parenquimatic structures is only present in some groups and finally they exhibit sexual and nonsexual reproduction. By contrast, plants have an elevated level of differentiation like, for example, roots, leafs, vascular network xylem/phloem [4, 5], and other specific characteristics.
