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We all know plants like pines, oaks or beech. We all know seaweed such as sea lettuce, wakame or others used in Japanese cuisine. But do we really know what plants and algae are? Well, as we might well suppose, the answer is no. All the organisms mentioned above are evolutionarily related and belong to the same group, that of plants. However, algae are also called another group of organisms less known and less evolutionarily related, cyanobacteria, belonging to the kingdom of bacteria. If you want to know what the similarities and differences between algae and plants Keep reading because at Ecologista Verde we reveal the answer to you.
Evolutionary history to better understand plants and algae
Molecular analysis of ribosomal RNA from living beings at the end of the 70s allowed its division into three large domains: Bacteria, Archaea and Eukarya. The first two, Bacteria and Archaea, are formed by prokaryotic organisms and the third by eukaryotic organisms. The Eukarya domain is home to great biological diversity including unicellular and multicellular organisms, autotrophs and heterotrophs.
The first eukaryotic organisms according to the Endosymbiosis Theory (Lynn Margulis, 1967) come from the fusion of two prokaryotic organisms, one of which had the ability to breathe oxygen, which gave rise to mitochondria. Later, this primitive eukaryote would engulf a photosynthetic cyanobacterium, which became integrated into the cell and gave rise to the current chloroplasts of plant cells.
The knowledge of the origin of plant cells and subsequent phylogenetic analyzes have allowed us to know the relationship that exists between plant species and how and when they have diversified. These analyzes suggest that green algae and terrestrial plants (chlorobionts), red algae (rhodophytes), and a small group of freshwater unicellular algae (glaucophytes) descend from a common ancestor. This common ancestor would be the first eukaryote to acquire chloroplasts about 1.5 billion years ago. This monophyletic group is called Plantae or Archaeplastida.
What is a plant and what is an algae
The first of all is to explain a series of concepts widely used in evolutionary biology and taxonomy that help us better understand the kinship relationships between species: monophyletic, paraphyletic and polyphyletic groups. A monophyletic group is one that includes a common ancestor and all its descendants. A paraphyletic group does include the common ancestor but not all descendants, and a polyphyletic group includes species with different ancestors.
Understood this let's see what is a plant and what is an alga. For plants to be a monophyletic group, terrestrial plants, called Embryophytes, Glaucophytes, Rhodophytes and Chlorophytes must be included. The terrestrial plants or embryophytes They include non-vascular plants such as bryophytes (liverworts and mosses), and vascular plants such as ferns and seed plants (gymnosperms and angiosperms). However, terrestrial plants would be a paraphyletic group by not including all the descendants of the ancestor that originated them.
In contrast, the concept of "alga" broadly includes all photosynthetic eukaryotic organisms other than land plants. Thus the seaweed they would form a paraphyletic group. But they are also algae, or rather we call them that, cyanobacteria, photosynthetic prokaryotic organisms, which have a very different origin from the rest of the other algae (Glaucophytes, Rhodophytes and Chlorophytes). In this way, what we call algae would correspond to a polyphyletic group without any evolutionary or taxonomic meaning.
Therefore, we could conclude that the plants or the monophyletic group Plantae includes all terrestrial and aquatic plants (Embryophytes), and some algae (Chlorophytes, Rhodophytes, Glaucophytes). And on the other hand, that the group of algae consists of several photosynthetic eukaryotic descendants of the original ancestor of the group Plantae and by cyanobacteria, photosynthetic prokaryotic organisms.
Well, once we know what plants and algae are, we are going to see their similarities and differences. In this article, eukaryotic algae will be discussed, since cyanobacteria are less related organisms and for this we should better talk about similarities and differences between prokaryotic and eukaryotic organisms.
Similarities between plants and algae
We start with the similar points between these two types of living things. These are the main similarities between plants and algae:
- Have chloroplasts with two membranes. The existence of the two membranes suggests that in this group the organelles that enable photosynthesis evolved from an endosymbiotic event between a primitive eukaryotic ancestor and photosynthetic cyanobacteria. The chloroplasts of plant cells have chlorophyll.
- Chlorophytes, Rhodophytes, Glaucophytes, and Embryophytes store starch as a reserve carbohydrate.
- Cell mitochondria often have flattened ridges. Mitochondria are the organelles where it takes place cellular respiration, a process by which the cell consumes oxygen and organic matter in exchange for energy.
- Cell walls are made up of cellulose polysaccharides.
- Perform photosynthesis. Thanks to solar energy they fix CO2 and produce oxygen and organic matter that they will need to carry out cellular respiration and obtain energy.
- Are autotrophs, that is, they manufacture their organic matter from inorganic. Concept related to photosynthesis.
- Both algae and plants can live in aquatic and terrestrial environments.
Differences between plants and algae
Finally, we indicate the main differences between plants and algae. Before, we return to highlight what has been explained in the definition. The land plants, understood as Embryophytes, would form a paraphyletic group while the seaweed, including cyanobacteria, would form a polyphyletic group. Therefore, we are going to see the differences between Embryophytes (Terrestrial Plants) and algae.
- Differences in the level of structural complexity. All embryophytes are multicellular while algae can be multicellular or unicellular, like glaucophytes.
- Embryophytes, as their name suggests, go through a embryonic state in some of the phases of its life while in algae this does not happen. In embryophytes, during their development, the embryo develops and gives rise to a diploid multicellular sporophyte.
- Embryophytes can develop reproductive structures specialized, such as flowers.
- Although algae and embryophytes share photosynthetic pigments, some such as phycobilins are unique to algae such as Rhodophytes and Glaucophytes, although these can also be found in cyanobacteria.
- Although we have commented that both algae and embryophytes share the same habitatsIt is true that algae generally live in aquatic environments and plants have adapted much better to the terrestrial environment.
- Algae have no true tissues, tissue being understood as a group of specialized cells that perform a specific function. In the case of cells, the tissues of the leaves, stems and roots are different.
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