23.2B: Protist Life Cycles and Habitats
- Describe the habitats and life cycles of various protists
Life Cycle of Slime Molds
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, which is a strategy also employed by animals. Other protists have multicellular stages in both haploid and diploid forms, a strategy called alternation of generations that is also used by plants.
Plasmodial slime molds
The slime molds are categorized on the basis of their life cycles into plasmodial or cellular types. Plasmodial slime molds are composed of large, multinucleate cells and move along surfaces like an amorphous blob of slime during their feeding stage. The slime mold glides along, lifting and engulfing food particles, especially bacteria. Upon maturation, the plasmodium takes on a net-like appearance with the ability to form fruiting bodies, or sporangia, during times of stress. Meiosis produces haploid spores within the sporangia. Spores disseminate through the air or water to potentially land in more favorable environments. If this occurs, the spores germinate to form amoeboid or flagellate haploid cells that can combine with each other and produce a diploid zygotic slime mold to complete the life cycle.
Cellular slime molds
The cellular slime molds function as independent amoeboid cells when nutrients are abundant. When food is depleted, cellular slime molds aggregate into a mass of cells that behaves as a single unit called a slug. Some cells in the slug contribute to a 2–3-millimeter stalk, which dries up and dies in the process. Cells atop the stalk form an asexual fruiting body that contains haploid spores. As with plasmodial slime molds, the spores are disseminated and can germinate if they land in a moist environment. One representative genus of the cellular slime molds is Dictyostelium , which commonly exists in the damp soil of forests.
Habitats of Various Protists
There are over 100,000 described living species of protists. Nearly all protists exist in some type of aquatic environment, including freshwater and marine environments, damp soil, and even snow. Paramecia are a common example of aquatic protists. Due to their abundance and ease of use as research organisms, they are often subjects of study in classrooms and laboratories. In addition to aquatic protists, several protist species are parasites that infect animals or plants and, therefore, live in their hosts. Amoebas can be human parasites and can cause dysentery while inhabiting the small intestine. Other protist species live on dead organisms or their wastes and contribute to their decay. Approximately 1000 species of slime mold thrive on bacteria and fungi within rotting trees and other plants in forests around the world, contributing to the life cycle of these ecosystems.
Contributions and Attributions
- OpenStax College, Biology. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44616/latest...ol11448/latest . License : CC BY: Attribution
- OpenStax College, Biology. October 23, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44616/latest...ol11448/latest . License : CC BY: Attribution
- OpenStax College, Biology. November 14, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44629/latest...ol11448/latest . License : CC BY: Attribution
- phagocytosis. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/phagocytosis . License : CC BY-SA: Attribution-ShareAlike
- multinucleate. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/multinucleate . License : CC BY-SA: Attribution-ShareAlike
- phagosome. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/phagosome . License : CC BY-SA: Attribution-ShareAlike
- amorphous. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/amorphous . License : CC BY-SA: Attribution-ShareAlike
- pellicle. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/pellicle . License : CC BY-SA: Attribution-ShareAlike
- taxis. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/taxis . License : CC BY-SA: Attribution-ShareAlike
- OpenStax College, Characteristics of Protists. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44616/latest..._B23_02_02.jpg . License : CC BY: Attribution
- OpenStax College, Characteristics of Protists. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44616/latest..._B23_02_01.jpg . License : CC BY: Attribution
- OpenStax College, Biology. October 23, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44616/latest...ol11448/latest . License : CC BY: Attribution
- OpenStax College, Biology. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44616/latest...ol11448/latest . License : CC BY: Attribution
- OpenStax College, Groups of Protists. November 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44617/latest/ . License : CC BY: Attribution
- plasmodium. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/plasmodium . License : CC BY-SA: Attribution-ShareAlike
- diploid. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/diploid . License : CC BY-SA: Attribution-ShareAlike
- haploid. Provided by : Wiktionary. Located at : en.wiktionary.org/wiki/haploid . License : CC BY-SA: Attribution-ShareAlike
- sporangia. Provided by : Wikipedia. Located at : en.Wikipedia.org/wiki/sporangia . License : CC BY-SA: Attribution-ShareAlike
- OpenStax College, Characteristics of Protists. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44616/latest..._B23_02_02.jpg . License : CC BY: Attribution
- OpenStax College, Characteristics of Protists. October 16, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44616/latest..._B23_02_01.jpg . License : CC BY: Attribution
- OpenStax College, Groups of Protists. November 18, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44617/latest/ . License : CC BY: Attribution
- OpenStax College, Groups of Protists. November 18, 2013. Provided by : OpenStax CNX. Located at : http://cnx.org/content/m44617/latest/ . License : CC BY: Attribution
Key Points
- Slime molds are categorized on the basis of their life cycles into plasmodial or cellular types, both of which end their life cycle in the form of dispersed spores.
- Plasmodial slime molds form a single-celled, multinucleate mass, whereas cellular slime molds form an aggregated mass of separate amoebas that are able to migrate as a unified whole.
- Slimes molds feed primarily on bacteria and fungi and contribute to the decomposition of dead plants.
Key Terms
- haploid : of a cell having a single set of unpaired chromosomes
- sporangia : an enclosure in which spores are formed (also called a fruiting body)
- plasmodium : a mass of cytoplasm, containing many nuclei, created by the aggregation of amoeboid cells of slime molds during their vegetative phase
- diploid : of a cell, having a pair of each type of chromosome, one of the pair being derived from the ovum and the other from the spermatozoon