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protists

by Kdesilva
Last updated 7 years ago

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Why are Protists no longer considered a Kingdom?"In the past, taxonomists classified all protists in a single kingdom, Protista. However, it is now clear that Protista is in fact paraphyletic. Some protists are more closely related to plants, fungi, or animals than they are to other protists. As a result, the kingdom Protista has been abandoned.Various lineages are recognized as kingdoms in their own right."

PROTISTS

How did cholorplasts and mitochondria evolve through endosymbiosis?"Much of protist diversity is the result of endosymbiosis, a process in which unicellular organisms engulfed other cells that evolved into organelles in the host cell.The earliest eukaryotes acquired mitochondria by engulfing alpha proteobacteria. The early origin of mitochondria is supported by the fact that all eukaryotes studied so far either have mitochondria or had them in the past. Later in eukaryotic history, one lineage of heterotrophic eukaryotes acquired an additional endosymbiont—a photosynthetic cyanobacterium—that evolved into plastids. This lineage gave rise to red and green algae. This hypothesis is supported by the observation that the DNA of plastids in red and green algae closely resembles the DNA of cyanobacteria.Plastids in these algae are surrounded by two membranes, presumably derived from the cell membranes of host and endosymbiont. On several occasions during eukaryotic evolution, red and green algae underwent secondary endosymbiosis. They were ingested in the food vacuole of a heterotrophic eukaryote and became endosymbionts themselves. For example, algae known as chlorarachniophytes evolved when a heterotrophic eukaryote engulfed a green alga. This process likely occurred comparatively early in evolutionary time, because the engulfed alga still carries out photosynthesis with its plastids and contains a tiny, vestigial nucleus called a nucleomorph."

Multicelluler and Unicellular .Divided into protozoans and algae."Protists exhibit more structural and functional diversity than any other group of organisms."

Metabolism:-Phototrophs, heterotrophs, and mixotrophs.Reproduction:-Produce asexually and sexually-Reproduce or grow by mitosis(Binary Divsion), conjugation, and some reproduce by meiosis and fertilization.Where it Lives:-Thermal springs, briny pools, cave waters, snow and ice, beach sands and intertidal mud flats, bogs and marshes, swimming pools, and sewage treatment plants.Respiration:-Anaerobic and Aerobic Respiration-Hydrogenosomes or specialized symbiotic bacteria act as respiratory organelles.

By: Kelsey De SilvaAP Biology-C


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