Paramecium, showing contractile vacuole and also ciliary motion. Paramecium lives in fresh 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 opened in the cell membrane. The sweeping activity of the hair-like cilia helps the single-celled biology move. Differential interference contrast, 350x-1000x. Tenth Prize, 2013 Olympus BioScapes Digital Imaging Competition®. credit: Ralph Grimm, Jimboomba Queensland, Australia.)
Paramecia room single-celled protists that room naturally discovered in aquatic habitats. Castle are frequently oblong or slipper-shaped and are covered with short hairy structures referred to as cilia. Specific paramecia are likewise easily cultured in labs and also serve as useful model organisms.

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

Paramecia space a part of a team of organisms recognized as ciliates. Together the name suggests, their bodies space covered in cilia, or short hairy protrusions. Cilia are necessary for activity of paramecia. Together these structures whip ago and forth in one aquatic environment, lock propel the organism with its surroundings. Paramecia have the right to move forward at rates up come 2 millimeters per second, as José de Ondarza, an combine professor in the room of organic Sciences in ~ SUNY Plattsburgh notes on his study website. Sometimes the biology will carry out "avoidance reactions" through reversing the direction in which the cilia beat. This outcomes in stopping, rotate or turning, ~ which point the paramecium resumes swim forward. If multiple avoidance reactions monitor one another, it is feasible for a paramecium come swim backward, though not as smoothly together swimming forward.

Cilia also assist in feeding by advertise food right into a rudimentary mouth opening known as the oral groove. Paramecia feed primarily on bacteria, however are known to eat yeast, unicellular algae and also even part non-living building materials such as milk powder, starch and also powdered charcoal, follow to "Biology of Paramecium."

Cell structure

Paramecia room eukaryotes. In contrast to prokaryotic organisms, such as bacteria and archaea, eukaryotes have actually well-organized cells. The specifying features of eukaryotic cells room the presence of dedicated membrane-bound to move machinery dubbed organelles and the nucleus, i m sorry is a compartment that holds DNA. Paramecia have many organelles properties of all eukaryotes, such together the energy-generating mitochondria. However, the organism also contains some distinctive organelles.

Under an outside covering called the pellicle is a class of somewhat firm cytoplasm called the ectoplasm. This an ar consists that spindle-shaped organelles well-known as trichocysts. When they discharge your contents, they come to be long, thin and spiky, according to "Biology of Paramecium." The exact role of trichocysts is not quite clear, despite a well-known theory is that they are crucial for defense versus predators. This has actually been tested over the years and also has organized true for particular Paramecium species against certain predators. For example, a 2013 article published in the journal Zoological Science discovered that trichocysts the Paramecium tetraurelia were effective versus two of the 3 predators the were tested: the Cephalodella species that rotifers and the Eucypris species the arthropods.

Below the ectoplasm lies a more fluid kind of cytoplasm: the endoplasm. This region contains the bulk of cell components and organelles, consisting of vacuoles. These space membrane-enclosed pockets in ~ a cell. Follow to a 2013 document published in the newspaper Bioarchitecture, the surname "vacuole" explains the reality that they appear transparent, and empty. In actuality, this organelles have tendency to be filled with fluid and also other materials. Vacuoles take on specific functions with a paramecium cell. Food secret encapsulate food consumed by the paramecium. They then fuse through organelles called lysosomes, who enzymes rest apart food molecules and also conduct a form of digestion. Contractile vacuoles are responsible because that osmoregulation, or the discharge of overabundance water from the cell, according to the authors of "Advanced Biology, first Ed." (Nelson, 2000). Relying on the species, water is fed into the contractile secret via canals, or by smaller sized water-carrying vacuoles. When the contractile vacuole collapses, this overabundance water leaves the paramecium body through a spicy in the pellicle ("Biology of Paramecium").

Perhaps the most unusual characteristics of paramecia is your nuclei. "Paramecium together with the other ciliates have this rather distinct feature," stated James Forney, a professor that biochemistry at Purdue University. "They have actually two varieties of nuclei, which differ in your shape, your content and also function."

The two species of nuclei space the micronucleus and macronucleus. The micronucleus is diploid; the is, it has two duplicates of every paramecium chromosome. Forney notes that the micronucleus contains every one of the DNA that is current in the organism. "It"s the DNA that is passed indigenous one generation to the an additional during sexual reproduction," that said. ~ above the various other hand, the macronucleus includes a subset that DNA native the micronucleus, according to Forney. "It is the transcriptionally active nucleus," he added. "So it"s the nucleus the is spelling, orthography to make mRNAs and proteins indigenous those mRNAs." The macronucleus is polyploid, or includes multiple copies of each chromosome, sometimes up to 800 copies.

All Paramecium species have one macronucleus, follow to Forney. However the variety of micronuclei have the right to vary by species. He offers the example of the Paramecium aurelia types complex, which have actually two micronuclei and Paramecium multimicronucleatum, which have several.

Why the presence of two distinct nuclei? One evolutionary reason is that it is a mechanism whereby paramecia and other ciliates deserve to stave off genetic intruders: piece of DNA that embed themselves right into the genome. "In the case of ciliates, there"s a device in which, if a item 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 various other words, if something foreign got right into the micronuclear genome, then as soon as the following macronucleus is made, it would removed and not included in the expressed version the the genome." Forney notes that this has been defined by some as a primitive DNA immune system; that is, surveying the genome and trying to keep out invading elements.


Diagram that a paramecium. (Image credit: Designua Shutterstock


Paramecia can reproduce one of two people asexually or sexually, relying on their eco-friendly conditions. Asexual reproduction takes ar when ample nutrients are available, while sex-related reproduction takes location under problems of starvation. In addition, paramecia can likewise undergo "autogamy" or self-fertilization under problems of an extensive starvation, follow to de Ondarza’s study website.

Asexual reproduction (binary fission)

During binary fission, one paramecium cabinet divides into two genetically the same offspring, or daughter cells. According to Forney, the micronucleus undergoes mitosis, however the macronucleus divides another way, dubbed an amitotic, or non-mitotic, mechanism. "It is not based upon mitosis but it divides between the 2 cells and also somehow is able come keep approximately the same number of copies of every gene," that said.

Sexual reproduction (conjugation)

Conjugation among paramecia is akin to mating. Forney said that there are two mating species for paramecia, i m sorry are described as odd and even. This shows the reality that the mating varieties for assorted Paramecium species room denoted by one of two people an odd or even number. Because that example, follow to Forney, Paramecium tetraurelia have mating varieties 7 and also 8. "Odd will certainly mate through the also mating kind but you cannot mate if you are the very same mating type," he said. Moreover, just cells within a single Paramecium species have the right to mate with one another.

The procedure is conveniently distinguishable under activities conditions. "The cells stick together. They deserve to actually type rather dramatic clumps that cells once they are at first mixed," Forney said. "Then those gradually pair off right into individual pairs in culture."

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

Autogamy (self-fertilization)

"Autogamy is essentially the exact same thing together conjugation, yet it is just happening with a solitary cell," Forney said. Throughout this process, the micronucleus replicates many times. Among these brand-new micronuclei undergo rearrangement the their hereditary content. Part DNA is fragmented and also some DNA sequences, well-known as "Internal removed Sequences," space removed, follow to de Ondarza’s study website.


The basic term "paramecium" describes a single organism in ~ the genus Paramecium. A genus, according to Oregon State University, refers to a closely related team of organisms the share comparable characteristics. The genus Paramecium is further split in teams known together subgenera, which every contain one or more species.

The techniques of classifying paramecia have changed over the years. The earliest approaches were with visual observation and also were based upon morphology, at some point describing every paramecia as either aurelia or bursaria. Much more recently, category has an unified morphological monitoring with molecular and genetic information. This has actually helped to develop a family members tree, known as a phylogenetic tree, the represents evolution relationships. This transition from morphology to molecule phylogenetics has influenced the knowledge of relationship within theParamecium genus and species diversity, according to Michaela Strüder-Kypke, manager of advanced light microscopy in ~ the Molecular and also Cellular Imaging basic at the college of Guelph in Ontario, Canada. She said that as of 2012, over there are five subgenera normally supported by molecular phylogeny to differing degrees: Chloroparamecium, Helianter, Cypriostomum, Viridoparamecium and Paramecium.

Strüder-Kypke said that a technique of identifying varieties known as "DNA barcoding" has been supplied for Paramecium. "Identification of varieties based on the succession of a specific fragment of DNA has been described as DNA barcoding," she explained. "Just like a barcode in the stores identifies every product, a quick DNA sequence that is sufficiently divergent, can identify every species." One together barcode, the cox1 gene, has been "extensively utilized for the genus Paramecium," Strüder-Kypke said.

There are right now 19 known morphospecies that Paramecium, follow to Strüder-Kypke. She described that a morphospecies is a types defined just by unique morphological characteristics, no by genetics or the capacity to produce fertile offspring. The this, 15 sibling species form what is well-known as the Paramecium aurelia species complex. Sibling species, according to Strüder-Kypke, look at alike through no morphologically differentiating characteristics, but they different in biochemical and genetic aspects and also cannot conjugate with one another. The Paramecium aurelia complex counts together a solitary morphospecies.

New insights right into Paramecium taxonomy and also the presence of brand-new species continue to be explained even today. The 19th morphospecies,Paramecium buetschlii, was uncovered in a freshwater pool in Norway and described in a 2015 research paper, released in the newspaper Organisms Diversity & Evolution. The same record also described three brand-new "cryptic species" found in Germany, Hungary and Brazil. The authors describe that they were treated as cryptic species because they were daunting to differentiate morphologically from other members of theParamecium genus. However, taxonomic markers in your DNA show that they room a separate species.

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