How do Protists Reproduce

3 Key excerpts on "How do Protists Reproduce"

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  eBook - PDF

  Biology 2e

  • Mary Ann Clark, Jung Choi, Matthew Douglas(Authors)
  • 2018(Publication Date)
  • Openstax

    (Publisher)

  Some protists such as the true slime molds exhibit multiple fission and simultaneously divide into many daughter cells. Others produce tiny buds that go on to divide and grow to the size of the parental protist. Sexual reproduction, involving meiosis and fertilization, is common among protists, and many protist species can switch from asexual to sexual reproduction when necessary. Sexual reproduction is often associated with periods when nutrients are depleted or environmental changes occur. Sexual reproduction may allow the protist to recombine genes and produce new variations of progeny, some of which may be better suited to surviving changes in a new or changing environment. However, sexual reproduction is often associated with resistant 638 Chapter 23 | Protists This OpenStax book is available for free at http://cnx.org/content/col24361/1.8 cysts that are a protective, resting stage. Depending on habitat of the species, the cysts may be particularly resistant to temperature extremes, desiccation, or low pH. This strategy allows certain protists to “wait out” stressors until their environment becomes more favorable for survival or until they are carried (such as by wind, water, or transport on a larger organism) to a different environment, because cysts exhibit virtually no cellular metabolism. Protist life cycles range from simple to extremely elaborate. Certain parasitic protists have complicated life cycles and must infect different host species at different developmental stages to complete their life cycle. Some protists are unicellular in the haploid form and multicellular in the diploid form, a strategy employed by animals. Other protists have multicellular stages in both haploid and diploid forms, a strategy called alternation of generations, analogous to that used by plants. Habitats Nearly all protists exist in some type of aquatic environment, including freshwater and marine environments, damp soil, and even snow.

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  eBook - PDF

  The Biology of Reproduction

  • Giuseppe Fusco, Alessandro Minelli(Authors)
  • 2019(Publication Date)
  • Cambridge University Press

    (Publisher)

  Of the large and heterogeneous set of the remaining unicellular algae, we discuss here only some of the better-known groups and those with more remarkable phenomena of reproduction and sexuality; along- side these, we mention some groups of autotrophic unicellular eukaryotes once classified among the protozoans. 7.1 Protists (Unicellular Eukaryotes) All groups of unicellular eukaryotes (for a recent overview, see Archibald et al. 2017) can be referred to collectively as protists. Most protists reproduce by binary division, but multiple division is also widespread, especially among the parasitic taxa. In this case, the nucleus is divided repeatedly, giving rise to up to hundreds of nuclei. Binary division 342 takes place according to mechanisms that in many cases diverge significantly from the mitosis of metazoans or flowering plants. In fact, the nuclear envel- ope often remains intact during the separation of the chromosomes, in which case the mitotic spindle can be internal to the nuclear envelope, or external; in turn, the spindle can have the usual conformation, or be divided into two differently oriented half-spindles (Section 5.1.5). There are several types of multiple division, which often occur at different stages of a species’ life cycle; these types include budding and schizogony (Section 3.1.1.2). In some groups of protists, sexuality has never been observed. However, residual traces or indirect evidence of sexuality have been found in these species. For example, a more or less complete set of meiotic genes has been found in Entamoeba spp.

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  Origins of Sex

  • Mark Carlson Williams(Author)
  • 1977(Publication Date)
  • Yale University Press

    (Publisher)

  6 • THE EMERGENCE OF PROTISTS Symbiotic Bacteria and Organellar Sex NEW CELLS Present-day members of the kingdom Protoctista are as diverse as and more numerous than members of the kingdom Animalia or Plantae. Yet our knowledge of protoctists is still in its infancy. Nonetheless, a study of protoc-tists, and especially of the unicellular protoctists, by definition protists, is indispensable to an understanding of the origin of meiotic sex. The protists undergo more varieties of meiotic sex than any other kind of organism. All are capable of single-parent, asexual reproduction. In addition to the asexuality standard in this group, some protists have two-parent sexuality in their life cycle. Some divide mitotically, just like cells of our bodies cultured in the laboratory. Other cells undergo reduction division (meiosis) and subsequent fertilization, a sexual life cycle similiar to that of most animals and plants. Yet some protists divide by processes that are clearly simpler than mitosis and meiosis, and still others die whenever they atavistically engage in sex. The protoctist world thus provides us with a reflecting mirror into which we can look when speculating on the origins of mitosis and, later, of meiotic sex. Since mitosis and meiosis undoubtedly evolved in protoctists, we have included here an introduction to the biology of each of the major groups of this diverse and important kingdom. To understand the differences—and the similarities—between the an-cient bacterial style of sexuality that we have been discussing and modern modes of sex, such as the meiotic sexuality of animals, we must first recognize the evolution of a new kind of cell. This was the eukaryotic cell, or protist. In the thirty years since the French zoologist Edouard Chatton first pointed it 62

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