Paramecium, showing contractile vacuole and also ciliary motion. Paramecium lives in new water. The excess water it absorbs via osmosis is gathered into two contractile vacuoles, one at every end, which swell and expel water through an opening in the cabinet membrane. The sweeping motion of the hair-like cilia helps the single-celled organism move. Differential interference contrast, 350x-1000x. Tenth Prize, 2013 Olympus BioScapes Digital Imaging Competition®. credit: Ralph Grimm, Jimboomba Queensland, Australia.)
Paramecia space single-celled protists that room naturally discovered in aquatic habitats. Castle are frequently oblong or slipper-shaped and also are extended with quick hairy structures dubbed cilia. Specific paramecia are likewise easily cultured in labs and also serve as beneficial model organisms.

You are watching: What organelle allows free-living protists to expel extra water?



Paramecia cells are characteristically elongated. Historically, based on cell shape, these organisms were split into 2 groups: aurelia and also bursaria, follow to the "The biology of Paramecium, 2nd Ed." (Springer, 1986). The aurelia morphological kind is oblong, or "cigar" shaped, with a rather tapered posterior end. Bursaria, ~ above the various other hand, represents cell that space "slipper" shaped. They often tend to it is in shorter, and also their posterior finish is rounded.

Paramecia room a component of a team of organisms recognized as ciliates. Together the surname suggests, your bodies are covered in cilia, or short hairy protrusions. Cilia are necessary for activity of paramecia. Together these frameworks whip back and soon in one aquatic environment, castle propel the organism v its surroundings. Paramecia can move forward at rates up to 2 millimeters per second, as José de Ondarza, an combine professor in the department of biological Sciences in ~ SUNY Plattsburgh note on his study website. Occasionally the biology will carry out "avoidance reactions" through reversing the direction in which the cilia beat. This outcomes in stopping, rotate or turning, after ~ which suggest the paramecium resumes swim forward. If lot of avoidance reactions follow one another, it is feasible for a paramecium come swim backward, though not as smoothly as swimming forward.

Cell structure

Paramecia space eukaryotes. In contrast to prokaryotes organisms, such as bacteria and archaea, eukaryotes have actually well-organized cells. The specifying features of eukaryotic cells are the presence of dedicated membrane-bound cellular machinery referred to as organelles and also the nucleus, i m sorry is a compartment that holds DNA. Paramecia have plenty of organelles characteristic of all eukaryotes, such as the energy-generating mitochondria. However, the organism additionally contains some distinctive organelles.

Under an external covering called the pellicle is a layer of rather firm cytoplasm called the ectoplasm. This region consists of spindle-shaped organelles well-known as trichocysts. Once they discharge your contents, they become long, thin and spiky, according to "Biology that Paramecium." The exact role of trichocysts is not rather clear, though a popular theory is the they are essential for defense against predators. This has been tested end the years and has held true for particular Paramecium species against specific predators. Because that example, a 2013 write-up published in the journal Zoological Science discovered that trichocysts that Paramecium tetraurelia were effective against two that the three predators the were tested: the Cephalodella species of rotifers and also the Eucypris species of arthropods.

Below the ectoplasm lies a more fluid form of cytoplasm: the endoplasm. This region contains the bulk of cell components and organelles, consisting of vacuoles. These room membrane-enclosed pockets in ~ a cell. Follow to a 2013 document published in the newspaper Bioarchitecture, the surname "vacuole" explains the truth that they show up transparent, and empty. In actuality, this organelles often tend to be filled through fluid and other materials. Vacuoles take on certain functions v a paramecium cell. Food secret encapsulate food spend by the paramecium. They then fuse with organelles called lysosomes, whose enzymes break apart food molecules and also conduct a type of digestion. Contractile vacuoles room responsible because that osmoregulation, or the discharge of overfill water indigenous the cell, follow to the writer of "Advanced Biology, 1st Ed." (Nelson, 2000). Relying on the species, water is fed into the contractile vacuoles via canals, or by smaller water-carrying vacuoles. When the contractile vacuole collapses, this overabundance water pipeline the paramecium body v a sharp in the pellicle ("Biology that Paramecium").

Perhaps the most unusual properties of paramecia is your nuclei. "Paramecium together with the various other ciliates have this rather distinctive feature," said James Forney, a professor of biochemistry at Purdue University. "They have actually two types of nuclei, which differ in their shape, your content and also function."

The two species of nuclei space the micronucleus and macronucleus. The micronucleus is diploid; the is, it includes two duplicates of every paramecium chromosome. Forney notes that the micronucleus contains every one of the DNA the is existing in the organism. "It"s the DNA that is passed indigenous one generation come the one more during sex-related reproduction," the said. ~ above the other hand, the macronucleus includes a subset that DNA indigenous the micronucleus, according to Forney. "It is the transcriptionally energetic nucleus," he added. "So it"s the nucleus the is spelling to do mRNAs and proteins from those mRNAs." The macronucleus is polyploid, or has multiple duplicates of each chromosome, sometimes up to 800 copies.

All Paramecium species have one macronucleus, follow to Forney. But the number of micronuclei can vary by species. He gives the example of the Paramecium aurelia types complex, which have two micronuclei and Paramecium multimicronucleatum, which have actually several.

Why the visibility of two distinctive nuclei? One evolutionary factor is the it is a mechanism through which paramecia and other ciliates can stave off genetic intruders: pieces of DNA the embed themselves into the genome. "In the situation of ciliates, there"s a device in which, if a piece of DNA is in the micronucleus but it"s not in the macronucleus, it will certainly be removed from the next macronucleus that is made," Forney explained. "In other words, if something international got right into the micronuclear genome, then once the following macronucleus is made, it would certainly removed and also not contained in the expressed variation of the genome." Forney notes that this has actually been explained by some as a primitive DNA immune system; the is, surveying the genome and also trying to store out invading elements.


Diagram the a paramecium. (Image credit: Designua Shutterstock


Paramecia have the right to reproduce either asexually or sexually, relying on their eco-friendly conditions. Asexual reproduction takes location when ample nutrients room available, while sexual reproduction takes ar under problems of starvation. In addition, paramecia can likewise undergo "autogamy" or self-fertilization under conditions of an extensive starvation, follow to de Ondarza’s research study website.

Asexual reproduction (binary fission)

During binary fission, one paramecium cabinet divides right into two genetically the same offspring, or daughter cells. Follow to Forney, the micronucleus experience mitosis, but the macronucleus divides an additional way, referred to as an amitotic, or non-mitotic, mechanism. "It is not based upon mitosis yet it divides in between the two cells and also somehow is able to keep around the same number of copies of every gene," the said.

Sexual reproduction (conjugation)

Conjugation among paramecia is akin to mating. Forney stated that there room two mating varieties for paramecia, which are referred to as odd and also even. This shows the fact that the mating species for assorted Paramecium species are denoted by one of two people an strange or also number. For example, follow to Forney, Paramecium tetraurelia have actually mating types 7 and 8. "Odd will mate v the even mating type but you can not mate if you are the exact same mating type," that said. Moreover, just cells within a single Paramecium species have the right to mate with one another.

The procedure is conveniently distinguishable under laboratory conditions. "The cells stick together. They have the right to actually type rather dramatic clumps the cells once they are initially mixed," Forney said. "Then those slowly pair off into individual pairs in culture."

During sex-related reproduction, the micronuclei of each paramecium undergo meiosis, eventually halving the genetic content to develop a haploid nucleus. These are exchanged in between the two connected mates. The haploid nuclei from every mate fuse to produce a new, gene varied, micronucleus. In turn, the new micronucleus replicates to provide rise come a brand-new macronucleus, follow to de Ondarza’s research study website.

Autogamy (self-fertilization)

"Autogamy is basically the exact same thing together conjugation, however it is only happening v a single cell," Forney said. During this process, the micronucleus replicates lot of times. One of these new micronuclei experience rearrangement the their genetic content. Some DNA is fragmented and some DNA sequences, well-known as "Internal got rid of Sequences," space removed, according to de Ondarza’s research website.


The general term "paramecium" describes a single organism within the genus Paramecium. A genus, according to Oregon State University, describes a closely related group of organisms that share similar characteristics. The genus Paramecium is further separated in groups known together subgenera, which each contain one or much more species.

The methods of classifying paramecia have readjusted over the years. The earliest approaches were v visual observation and were based on morphology, eventually describing every paramecia as either aurelia or bursaria. Much more recently, classification has merged morphological observation with molecular and also genetic information. This has actually helped to build a family tree, known as a phylogenetic tree, the represents evolutionary relationships. This shift from morphology to molecule phylogenetics has influenced the understanding of relationship within theParamecium genus and types diversity, follow to Michaela Strüder-Kypke, manager of advanced light microscopy in ~ the Molecular and Cellular Imaging facility at the college of Guelph in Ontario, Canada. She said that together of 2012, over there are 5 subgenera usually supported by molecule phylogeny to varying degrees: Chloroparamecium, Helianter, Cypriostomum, Viridoparamecium and Paramecium.

Strüder-Kypke claimed that a an approach of identifying types known together "DNA barcoding" has actually been used for Paramecium. "Identification of types based ~ above the succession of a certain fragment the DNA has actually been referred to as DNA barcoding," she explained. "Just like a barcode in the shop identifies each product, a brief DNA sequence that is saturated divergent, have the right to identify every species." One together barcode, the cox1 gene, has actually been "extensively used for the genus Paramecium," Strüder-Kypke said.

There are at this time 19 recognized morphospecies of Paramecium, according to Strüder-Kypke. She explained that a morphospecies is a species defined just by distinct morphological characteristics, no by genetics or the ability to create fertile offspring. That this, 15 sibling species form what is well-known as the Paramecium aurelia species complex. Sibling species, follow to Strüder-Kypke, look alike v no morphologically separating characteristics, however they differ in biochemical and also genetic aspects and cannot conjugate v one another. The Paramecium aurelia complex counts as a solitary morphospecies.

New insights into Paramecium taxonomy and the presence of brand-new species continue to be defined even today. The 19th morphospecies,Paramecium buetschlii, was found in a freshwater swimming pool in Norway and described in a 2015 study paper, published in the journal Organisms Diversity & Evolution. The same record also explained three new "cryptic species" discovered in Germany, Hungary and Brazil. The authors describe that they were treated as cryptic species because they were an overwhelming to identify morphologically from other members that theParamecium genus. However, taxonomic markers in your DNA indicate that they are a separate species.

See more: How Do Write 54 As A Product Of Prime Factors., How Do You Write 54 As A Product Of Prime Factors

"The idea is that, if we look in unexplained habitats or "under sampled" areas of this world, we might still find new species," Strüder-Kypke told