49-474: Closteriaceae Desmidiaceae Gonatozygaceae Peniaceae Desmidiales , commonly called the desmids ( Gr. desmos , bond or chain), are an order in the Charophyta , a division of green algae in which the land plants ( Embryophyta ) emerged. Desmids consist of single-celled (sometimes filamentous or colonial) microscopic green algae. Because desmids are highly symmetrical, attractive, and come in
98-428: A fruit fly (mature after 10–14 days) can produce up to 900 offspring per year. These two main strategies are known as K-selection (few offspring) and r-selection (many offspring). Which strategy is favoured by evolution depends on a variety of circumstances. Animals with few offspring can devote more resources to the nurturing and protection of each individual offspring, thus reducing the need for many offspring. On
147-561: A diversity of forms, they are popular subjects for microscopists , both amateur and professional. The desmids belong to the class Zygnematophyceae . Although they are sometimes grouped together as a single family Desmidiaceae , most classifications recognize three to five families, usually within their own order, Desmidiales. The Desmidiales comprise around 40 genera and 5,000 to 6,000 species , found mostly but not exclusively in fresh water . In general, desmids prefer acidic waters (pH between 4.8 and 7.0), so many species may be found in
196-407: A much more complex task, but may well be possible to some degree according to current biological knowledge. A synthetic genome has been transferred into an existing bacterium where it replaced the native DNA, resulting in the artificial production of a new M. mycoides organism. There is some debate within the scientific community over whether this cell can be considered completely synthetic on
245-431: A narrow bridge or isthmus, wherein the spherical nucleus is located. Each semi-cell houses a large, often folded chloroplast for photosynthesizing . One or more pyrenoids can be found. These form carbohydrates for energy storage. The cell-wall, of two halves (termed semicells), which, in a few species of Closterium and Penium , are of more than one piece, has two distinct layers, the inner composed mainly of cellulose,
294-493: A new organism by combining the genetic material of two organisms in a process that starts with meiosis , a specialized type of cell division . Each of two parent organisms contributes half of the offspring's genetic makeup by creating haploid gametes . Most organisms form two different types of gametes. In these anisogamous species, the two sexes are referred to as male (producing sperm or microspores) and female (producing ova or megaspores). In isogamous species ,
343-413: A wide range of reproductive strategies employed by different species. Some animals, such as the human and northern gannet , do not reach sexual maturity for many years after birth and even then produce few offspring. Others reproduce quickly; but, under normal circumstances, most offspring do not survive to adulthood . For example, a rabbit (mature after 8 months) can produce 10–30 offspring per year, and
392-432: Is a stub . You can help Misplaced Pages by expanding it . Reproduction Reproduction (or procreation or breeding ) is the biological process by which new individual organisms – " offspring " – are produced from their "parent" or parents. There are two forms of reproduction: asexual and sexual . In asexual reproduction, an organism can reproduce without the involvement of another organism. Asexual reproduction
441-528: Is a process by which organisms create genetically similar or identical copies of themselves without the contribution of genetic material from another organism. Bacteria divide asexually via binary fission ; viruses take control of host cells to produce more viruses; Hydras ( invertebrates of the order Hydroidea ) and yeasts are able to reproduce by budding . These organisms often do not possess different sexes, and they are capable of "splitting" themselves into two or more copies of themselves. Most plants have
490-632: Is characterized by species such as Micrasterias ceratofera , while equatorial Africa is characterized by species such as Allorgeia incredibilis . Although desmids are incredibly diverse, with up to hundreds of them being found in a single site, their interactions with the environment are relatively unknown. Desmids are host to a wide array of parasites, particularly fungal parasites called chytrids . They are also grazed by microscopic aquatic heterotrophs , such as crustaceans , rotifers , and ciliates . Closteriaceae The Closteriaceae are one of four families of Charophyte green algae in
539-430: Is employed to exploit suitable conditions for survival such as an abundant food supply, adequate shelter, favorable climate, disease, optimum pH or a proper mix of other lifestyle requirements. Populations of these organisms increase exponentially via asexual reproductive strategies to take full advantage of the rich supply resources. When food sources have been depleted, the climate becomes hostile, or individual survival
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#1732793262512588-527: Is jeopardized by some other adverse change in living conditions, these organisms switch to sexual forms of reproduction. Sexual reproduction ensures a mixing of the gene pool of the species. The variations found in offspring of sexual reproduction allow some individuals to be better suited for survival and provide a mechanism for selective adaptation to occur. The meiosis stage of the sexual cycle also allows especially effective repair of DNA damages (see Meiosis ). In addition, sexual reproduction usually results in
637-450: Is not limited to single-celled organisms . The cloning of an organism is a form of asexual reproduction. By asexual reproduction, an organism creates a genetically similar or identical copy of itself. The evolution of sexual reproduction is a major puzzle for biologists. The two-fold cost of sexual reproduction is that only 50% of organisms reproduce and organisms only pass on 50% of their genes . Sexual reproduction typically requires
686-514: Is sometimes substituted for autogamous pollination (not necessarily leading to successful fertilization) and describes self-pollination within the same flower, distinguished from geitonogamous pollination , transfer of pollen to a different flower on the same flowering plant , or within a single monoecious gymnosperm plant. Mitosis and meiosis are types of cell division . Mitosis occurs in somatic cells , while meiosis occurs in gametes . Mitosis The resultant number of cells in mitosis
735-413: Is the growth and development of embryo or seed without fertilization . Parthenogenesis occurs naturally in some species, including lower plants (where it is called apomixis ), invertebrates (e.g. water fleas , aphids , some bees and parasitic wasps ), and vertebrates (e.g. some reptiles, some fish, and very rarely, domestic birds ). Sexual reproduction is a biological process that creates
784-409: Is twice the number of original cells. The number of chromosomes in the offspring cells is the same as that of the parent cell. Meiosis The resultant number of cells is four times the number of original cells. This results in cells with half the number of chromosomes present in the parent cell. A diploid cell duplicates itself, then undergoes two divisions ( tetraploid to diploid to haploid), in
833-430: The ciliate Paramecium aurelia , have more than two "sexes", called mating types . Most animals (including humans) and plants reproduce sexually. Sexually reproducing organisms have different sets of genes for every trait (called alleles ). Offspring inherit one allele for each trait from each parent. Thus, offspring have a combination of the parents' genes. It is believed that "the masking of deleterious alleles favors
882-540: The order Desmidiales (desmids). It contains two genera, Closterium and Spinoclosterium . Closteriaceae consists of individual cells that are longer than wide. The cell shape ranges from straight to curved (lunate), with some species having cells curved only at the poles. The cell wall is hyaline or brownish in color, and may be covered with various ornamentation such as grooves, ribs, scores, and polar thickenings. Cells contain axial chloroplasts with several pyrenoids . This green algae -related article
931-459: The Desmidiales. The structure of these algae is unicellular , and lacks flagella . Although most desmid species are unicellular, some genera form chains of cells, called filaments. A few genera form non-filamentous colonies, with individual cells connected by threads or remnants of parent cell walls. The cell of a desmid is often divided into two symmetrical compartments separated by
980-665: The ability to reproduce asexually and the ant species Mycocepurus smithii is thought to reproduce entirely by asexual means. Some species that are capable of reproducing asexually, like hydra , yeast (See Mating of yeasts ) and jellyfish, may also reproduce sexually. For instance, most plants are capable of vegetative reproduction – reproduction without seeds or spores – but can also reproduce sexually. Likewise, bacteria may exchange genetic information by conjugation . Other ways of asexual reproduction include parthenogenesis , fragmentation and spore formation that involves only mitosis . Parthenogenesis
1029-541: The basis for their classification. The largest among them may be visible to the unaided eye. Desmids possess characteristic crystals of barium sulphate at either end of the cell which exhibit continuous Brownian motion . The function of these crystals is completely unknown. Many desmids also secrete translucent, gelatinous mucilage from pores in the cell wall that acts as a protecting agent. These pores are either, as in Micrasterias , uniformly distributed across
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#17327932625121078-472: The boundaries between life and machines until the two overlap to yield "truly programmable organisms". Researchers involved stated that the creation of "true synthetic biochemical life" is relatively close in reach with current technology and cheap compared to the effort needed to place man on the Moon. Sexual reproduction has many drawbacks, since it requires far more energy than asexual reproduction and diverts
1127-606: The canal passes. This is termed the pore-organ. The canals are no doubt in all cases occupied by threads of mucilage in process of excretion. At the inner surface of the wall they terminate in lens- or button-shaped swellings, while from the outer end of the pore-organ there sometimes arise delicate radiating or club-shaped masses of mucilage through which the canal passes and which appear to be more or less permanent in character. In most cases, however, these are absent or only represented by small perforated buttons. Desmids most commonly reproduce by asexual fission . During cell division,
1176-514: The cell-wall but always appear to be absent in the region of the isthmus, or, in highly ornamented forms, as many genera of Cosmarium , grouped symmetrically around the bases of the spines, warts and so on with which the cell is provided. In the inner layer of the wall the pore is a simple canal, but in the outer, except in Closterium , the canal is surrounded by a specially differentiated cylindrical zone, not composed of cellulose, through which
1225-436: The evolution of a dominant diploid phase in organisms that alternate between haploid and diploid phases" where recombination occurs freely. Bryophytes reproduce sexually, but the larger and commonly-seen organisms are haploid and produce gametes . The gametes fuse to form a zygote which develops into a sporangium , which in turn produces haploid spores. The diploid stage is relatively small and short-lived compared to
1274-411: The expression of a wider range of traits and thus making the population more able to survive environmental variation. Allogamy is the fertilization of flowers through cross-pollination, this occurs when a flower's ovum is fertilized by spermatozoa from the pollen of a different plant's flower. Pollen may be transferred through pollen vectors or abiotic carriers such as wind. Fertilization begins when
1323-602: The families and genera in the Desmidiales: The family Gonatozygaceae is sometimes included within the Peniaceae , reducing the number of families from four to three. A fifth family Mesotaeniaceae was formerly included in the Desmidiales, but analysis of cell wall structure and DNA sequences show that the group is more closely related to the Zygnemataceae , and so is now placed together with that family in
1372-449: The family Mesotaeniaceae in the order Zygnematales , consist of cells that are unconstricted at the middle, lack median suture lines, and do not have mucilage-secreting pores in the cell wall. Meanwhile, placoderm desmids, corresponding to the order Desmidiales, consist of cells with two symmetrical halves, and mucilage-secreting pores in the cell wall. Here, the term "desmids" and "placoderm desmids" will be used interchangeably to refer to
1421-439: The fissures between patches of sphagnum moss in marshes. As desmids are sensitive to changes in their environments, they are useful as bioindicators for water and habitat quality. The term "desmid" typically refers to a group of microscopic, mostly single-celled algae in the class Zygnematophyceae. Within the desmids, a distinction is typically made between "saccoderm" and "placoderm" desmids. Saccoderm desmids, corresponding to
1470-399: The formation of a life stage that is able to endure the conditions that threaten the offspring of an asexual parent. Thus, seeds, spores, eggs, pupae, cysts or other "over-wintering" stages of sexual reproduction ensure the survival during unfavorable times and the organism can "wait out" adverse situations until a swing back to suitability occurs. The existence of life without reproduction is
1519-401: The function of a few genes involved with imprinting, other Japanese scientists combined two mouse eggs to produce daughter mice and in 2018 Chinese scientists created 29 female mice from two female mice mothers but were unable to produce viable offspring from two father mice. Researches noted that there is little chance these techniques would be applied to humans in the near future. There are
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1568-402: The gametes are similar or identical in form ( isogametes ), but may have separable properties and then may be given other different names (see isogamy ). Because both gametes look alike, they generally cannot be classified as male or female. For example, in the green alga, Chlamydomonas reinhardtii , there are so-called "plus" and "minus" gametes. A few types of organisms, such as many fungi and
1617-692: The grounds that the chemically synthesized genome was an almost 1:1 copy of a naturally occurring genome and, the recipient cell was a naturally occurring bacterium. The Craig Venter Institute maintains the term "synthetic bacterial cell" but they also clarify "...we do not consider this to be "creating life from scratch" but rather we are creating new life out of already existing life using synthetic DNA". Venter plans to patent his experimental cells, stating that "they are pretty clearly human inventions". Its creators suggests that building 'synthetic life' would allow researchers to learn about life by building it, rather than by tearing it apart. They also propose to stretch
1666-402: The haploid stage, i.e. haploid dominance . The advantage of diploidy, heterosis, only exists in the diploid life generation. Bryophytes retain sexual reproduction despite the fact that the haploid stage does not benefit from heterosis. This may be an indication that the sexual reproduction has advantages other than heterosis, such as genetic recombination between members of the species, allowing
1715-402: The integrity of the genome to be maintained and offspring health to be protected. Scientific research is currently investigating the possibility of same-sex procreation, which would produce offspring with equal genetic contributions from either two females or two males. The obvious approaches, subject to a growing amount of activity, are female sperm and male eggs . In 2004, by altering
1764-442: The laboratory. Several scientists have succeeded in producing simple viruses from entirely non-living materials. However, viruses are often regarded as not alive. Being nothing more than a bit of RNA or DNA in a protein capsule, they have no metabolism and can only replicate with the assistance of a hijacked cell 's metabolic machinery. The production of a truly living organism (e.g. a simple bacterium) with no ancestors would be
1813-749: The order Zygnematales . However, the Zygnemataceae may have emerged in the Mesotaeniaceae . Desmids are found in freshwater habitats all over the world, but strongly prefer bogs, mires, and other nutrient-poor wetlands. They generally have strict ecological requirements: most species prefer waters with low amounts of dissolved calcium and magnesium, low salinity levels, and somewhat acidic pH. In waters with higher amounts of nutrients, desmids rapidly become outcompeted . Desmid species are generally found attached to aquatic vegetation, such as Utricularia , or tychoplanktonic ; that is, free-floating in
1862-484: The organisms from other pursuits, and there is some argument about why so many species use it. George C. Williams used lottery tickets as an analogy in one explanation for the widespread use of sexual reproduction. He argued that asexual reproduction, which produces little or no genetic variety in offspring, was like buying many tickets that all have the same number, limiting the chance of "winning" – that is, producing surviving offspring. Sexual reproduction, he argued,
1911-582: The other hand, animals with many offspring may devote fewer resources to each individual offspring; for these types of animals it is common for many offspring to die soon after birth, but enough individuals typically survive to maintain the population. Some organisms such as honey bees and fruit flies retain sperm in a process called sperm storage thereby increasing the duration of their fertility. Organisms that reproduce through asexual reproduction tend to grow in number exponentially. However, because they rely on mutation for variations in their DNA, all members of
1960-485: The outer is stronger and thicker, often furnished with spines, granules, warts et cetera. It is made up of a base of cellulose impregnated with other substances including iron compounds, which are especially prominent in some species of Closterium and Penium and is not soluble in an ammoniacal solution of copper oxide. Desmids assume a variety of highly symmetrical and generally attractive shapes, among those elongated, star-shaped and rotund configurations, which provide
2009-446: The pollen is brought to a female gamete through the pollen tube. Allogamy is also known as cross fertilization, in contrast to autogamy or geitonogamy which are methods of self-fertilization. Self- fertilization , also known as autogamy, occurs in hermaphroditic organisms where the two gametes fused in fertilization come from the same individual, e.g., many vascular plants , some foraminiferans , some ciliates . The term "autogamy"
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2058-555: The process forming four haploid cells. This process occurs in two phases, meiosis I and meiosis II. Animals, including mammals, produce gametes (sperm and egg) by means of meiosis in gonads (testicles in males and ovaries in females). Sperm are produced by spermatogenesis and eggs are produced by oogenesis . During gametogenesis in mammals numerous genes encoding proteins that participate in DNA repair mechanisms exhibit enhanced or specialized expression. Male germ cells produced in
2107-413: The sexual interaction of two specialized reproductive cells, called gametes , which contain half the number of chromosomes of normal cells and are created by meiosis , with typically a male fertilizing a female of the same species to create a fertilized zygote . This produces offspring organisms whose genetic characteristics are derived from those of the two parental organisms. Asexual reproduction
2156-446: The species have similar vulnerabilities. Organisms that reproduce sexually yield a smaller number of offspring, but the large amount of variation in their genes makes them less susceptible to disease. Many organisms can reproduce sexually as well as asexually. Aphids , slime molds , sea anemones , some species of starfish (by fragmentation ), and many plants are examples. When environmental factors are favorable, asexual reproduction
2205-441: The subject of some speculation. The biological study of how the origin of life produced reproducing organisms from non-reproducing elements is called abiogenesis . Whether or not there were several independent abiogenetic events, biologists believe that the last universal ancestor to all present life on Earth lived about 3.5 billion years ago . Scientists have speculated about the possibility of creating life non-reproductively in
2254-582: The testes of animals are capable of special DNA repair processes that function during meiosis to repair DNA damages and to maintain the integrity of the genomes that are to be passed on to progeny. Such DNA repair processes include homologous recombinational repair as well as non-homologous end joining . Oocytes located in the primordial follicle of the ovary are in a non-growing prophase arrested state, but are able to undergo highly efficient homologous recombinational repair of DNA damages including double-strand breaks. These repair processes allow
2303-533: The two halves of a cell separate, and each half develops into a new cell. After division, a cell may be asymmetric since the recently formed half is smaller than the original half. In adverse conditions, desmids may reproduce sexually through a process of conjugation , which are also found among other closely related taxa in the Zygnematophyceae . Sexual reproduction is rare, and many species have never been observed sexually reproducing. Classification of
2352-475: The water column after being disturbed. Although the Desmidiales are cosmopolitan, a number of species appear to be restricted to continents or biogeographical realms ; this is likely because desmids have strict ecological requirements and do not produce resting spores , making successful dispersal less likely. Therefore, they can be grouped into several regions each with their own characteristic desmid floras. The Indo-Malayan to North Australian realm, for example,
2401-420: Was like purchasing fewer tickets but with a greater variety of numbers and therefore a greater chance of success. The point of this analogy is that since asexual reproduction does not produce genetic variations, there is little ability to quickly adapt to a changing environment. The lottery principle is less accepted these days because of evidence that asexual reproduction is more prevalent in unstable environments,
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