What makes seaweed a protist

One of the defining characteristics of the Protista is that, unlike animals or plants, its members do not contain more than one clearly differentiated functional tissues. Kelp, for all their outward complexity and internal structure, are not considered to possess more than one clearly defined tissue type. This being the case, they cannot be considered plants, and for this and other reasons they clearly aren't animals or fungi either.

This leads to what is perhaps a more cynical, but frequently argued, view or even complaint : Protists are a group of organisms that are defined not as much by commonality but as by exclusion: a protist is simply something that is not an animal, or a plant, or a fungus, or a prokaryote.

So, much as it was in its first conception, the kingdom Protista in many regards may still represent the scrap pile of taxonomy -- it is where all of the misfits are thrown.

Of course, that can change. Why are kelp considered protists? Answer 1: To understand how kelp became members of the Protista, one must delve into the convoluted and messy history of systematics.

They are a large and diverse group. Some algae, the diatoms , are single-celled. Others, such as seaweed , are multicellular see Figure below.

Why are algae considered plant-like? The main reason is that they contain chloroplasts and produce food through photosynthesis. However, they lack many other structures of true plants. For example, algae do not have roots, stems, or leaves. Some algae also differ from plants in being motile.

They may move with pseudopods or flagella. Although not plants themselves, algae were probably the ancestors of plants. Algae play significant roles as producers in aquatic ecosystems. Microscopic forms live suspended in the water column. They are the main component of phytoplankton. As such, they contribute to the food base of most marine ecosystems. Multicellular seaweeds called kelp may grow as large as trees. They are the food base of ecosystems called kelp forests see Figure below.

Kelp forests are found throughout the ocean in temperate and arctic climates. They are highly productive ecosystems. Kelp Forest. This kelp forest supports a large community of many other types of organisms.

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