Different types of motility in protists : Protists use various methods for transportation. Protists live in a wide variety of habitats, including most bodies of water, as parasites in both plants and animals, and on dead organisms. 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. 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.
Plasmodial slime mold life cycle : Haploid spores develop into amoeboid or flagellated forms, which are then fertilized to form a diploid, multinucleate mass called a plasmodium. This plasmodium is net-like and, upon maturation, forms a sporangium on top of a stalk. The sporangium forms haploid spores through meiosis, after which the spores disseminate, germinate, and begin the life cycle anew.
The brightly-colored plasmodium in the inset photo is a single-celled, multinucleate mass. 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.
Cellular slime mold life cycle : Cellular slime molds may engage in two forms of life cycles: as solitary amoebas when nutrients are abundant or as aggregated amoebas inset photo when nutrients are scarce. In aggregate form, some individuals contribute to the formation of a stalk, on top of which sits a fruiting body full of spores that disseminate and germinate in the proper moist environment.
There are over , described living species of protists. This particular eukaryote is one of the smallest, simplest organisms in the domain, called a protist. As a human parasite, it can make us sick. Figure 1: This scanning electron micrograph revealed some of the external ultrastructural details displayed by a flagellated Giardia lamblia protozoan parasite, which is the organism responsible for causing the diarrheal disease "giardiasis".
Protists are a group of all the eukaryotes that are not fungi, animals, or plants. As a result, it is a very diverse group of organisms. The eukaryotes that make up this kingdom, Kingdom Protista , do not have much in common besides a relatively simple organization. Protists can look very different from each other. Some are tiny and unicellular, like an amoeba , and some are large and multicellular, like seaweed.
However, multicellular protists do not have highly specialized tissues or organs. This simple cellular-level organization distinguishes protists from other eukaryotes, such as fungi, animals, and plants. Many have both asexual and sexual reproduction. An example is a protist called Spirogyra , a type of algae, shown Figure below. It usually exists as haploid cells that reproduce by binary fission. In a stressful environment, such as one that is very dry, Spirogyra may produce tough spores that can withstand harsh conditions.
Spores are reproductive cells produced by protists and various other organisms. If two protist spores are close together, they can fuse to form a diploid zygote. This is a type of sexual reproduction. The zygote then undergoes meiosis, producing haploid cells that repeat the cycle. Spirogyra is a genus of algae with a complex life cycle. Each organism consists of rectangular cells connected end-to-end in long filaments.
Protists get food in one of three ways. They may ingest, absorb, or make their own organic molecules. Sexual or asexual reproduction for protists? Protist Habitats Most protists are aquatic organisms.
Motility of Protists Most protists have motility. Protists use cilia, pseudopods, or flagella to move. Protist Reproduction Protists have complex life cycles.
Protist Nutrition Protists get food in one of three ways.
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