What's The Deal With Plants and Algae?
Photosynthesis is the foundation for most of the foodwebs found on this planet that we call home and most people recognize plants as the champions of this complex process. But this only holds true on the land, because once one heads into the depths of the water they are entering a kingdom founded on the production of algae and other forgotten photosynthetic organisms. Today, we will still forget most of these photosynthesizers and highlight the differences between plants and their algal counterparts.
The first thing that one needs to understand about the mysterious organisms that pull energy directly from the rays of the sun that we are discussing today is that they are all members of Domain Eukarya in the tree of life. Organisms that belong under the eukaryote umbrella have complex eukaryotic cells with membrane-bound nuclei that contain their DNA as well as other organelles that carry out the various functions of the cell. This directly contrasts the prokaryotic organisms like bacteria that boast simple cells with no membrane-bound organelles and DNA that is not contained in a nucleus. For a bit of context, animals are also eukaryotes like the plants and algae we will be discussing in this article.
Let’s begin our exploration by focusing on algae. These organisms are often mistaken by the general population as annoying plants, but they are actually members of a kingdom that is currently being torn apart by a taxonomic civil war, Protista. The thing that protists have in common is that they are good at being so different that they do not fit into any of the other three major kingdoms in Domain Eukarya, and this especially holds true for those that are considered algae. Algae are so diverse that they cannot decide on existing as single-celled or multi-celled organisms, and some algal species exist as colonial organisms that fall somewhere between the two extremes. The difference between these three forms of existence is that single-celled organisms exist entirely as one cell that is not connected to any others, colonial organisms are essentially a connected pack of single-celled organisms, and multicellular organisms are a single creature made up of many cells with the same DNA.
No matter what kind of organism an algal species happens to be, it is likely found in an aquatic environment and carries out photosynthesis, but this does not mean that all algae are closely related. Algae are often split into groups based on the color that they predominantly boast, golden algae, yellow-green algae, red algae, brown algae, and green algae, but there are a few traits that they share that distinguish them from plants as a whole. Algal species lack specialization of cells and by extension organs to carry out specific functions, meaning that even in larger species the entire organism carries out all of the functions necessary for life. When species like giant kelp do get large enough to need some sort of anchor, they have evolved structures known as holdfasts that look similar to the roots of a plant, but the only function is to hold the algae in place. The holdfast, however, is a specialized anomaly in the algae world, not a widespread rule, as many algal species either float freely in the water column or retain some microscopic mobility structures.
If we now focus our attention on plants, we move on to Kingdom Plantae where all of the organisms are multicellular and sessile (attached to where they grow). At this point, it is important to note that the grouping of plants known as Bryophytes are considered primitive plants that lack vascular tissues and roots, but they still have specialization at the cellular level and organs that carry out specific functions. As you move further up the plant evolutionary tree the specialized structures become more obvious with roots for anchoring and nutrient absorption, flowers and fruits for reproduction, and other adaptations for protection and water efficiency. The main thing that distinguishes plants from algae is their specialization and their primarily terrestrial existence, of course, there are a couple of aquatic species, but they are the exception, not the rule.
To summarize the differences, algae are a very diverse group of organisms that exist on a spectrum ranging from uni- to multi-cellular, while plants have a common ancestor and are all multicellular. Plants also have a specialization that algae simply lack, and primarily occur on the land while algae remain aquatic organisms. No matter how different they may be, plants and algae both photosynthesize and help to form the foundations of the food webs where they exist.
References:
Raven Biology of Plants 8th edition (ISBN - 978-1429219617)
https://www.differencebetween.com/difference-between-algae-and-vs-plants/
