Funguslike Protists

Biologists recognize two groups of funguslike protists: slime molds and water molds. Slime molds are typically found on moist, decaying matter. They appear as glistening white, yellow, or red masses of slime, as shown in Figure 25-14. Slime molds have life cycles in which they spend part of their lives in a mobile, amoebalike feeding form, consuming organic matter and bacteria much as protozoa do. However, these protists have a stationary reproductive stage in which they produce a funguslike, spore-bearing structure called a fruiting body, shown in Figure 25-15. A water mold is a funguslike protist composed of branching filaments of cells. Water molds are found mainly in bodies of fresh water but sometimes live in soil or as parasites.

Phylum Myxomycota (Plasmodial Slime Molds)

The phylum Myxomycota (MIKS-oh-mie-KOH-tuh) includes about 700 species of plasmodial slime molds. During the feeding stage of its life cycle, a plasmodial slime mold is a mass of cytoplasm, called a plasmodium, that may be as large as several square meters. Each plasmodium is multinucleate, containing many diploid nuclei that are not separated by cell walls. As the plasmodium creeps along the forest floor by cytoplasmic streaming, it consumes decaying leaves and other debris by phagocytosis.

When food or water is scarce, the plasmodium begins to reproduce. It forms stalked fruiting bodies in which haploid spores are produced by meiosis. Spores are resistant to harsh conditions. Under favorable conditions, spores crack open and give rise to haploid reproductive cells. Two such cells fuse, and their nuclei combine to form a diploid nucleus. Repeated mitotic divisions follow, but the cells do not undergo cytokinesis. The lack of cytokinesis results in the multinucleated plasmodium.

Phylum Dictyostelida (Cellular Slime Mold)

The phylum Dictyostelida (dik-TEE-oh-STEL-uh-duh) includes about 65 species of cellular slime molds. Cellular slime molds live as individual haploid cells that move about like amoebas. Each cell moves as an independent organism, creeping over the ground or swimming in fresh water and ingesting food.

When food or water becomes scarce, the cells release a chemical that attracts nearby cells, causing them to gather by the thousands into a dense structure called a pseudoplasmodium. A pseudoplasmodium is a coordinated colony of individual cells that resembles a slug and leaves a slimy trail as it crawls. Although the cells move as one unit, each cell retains its membrane and identity. Eventually, the pseudoplasmodium settles and forms fruiting bodies in which haploid spores develop. When a fruiting body breaks open, the spores are dispersed. Each spore may grow into an individual amoeboid cell, thus completing the life cycle.

figure 25-14

Slime molds often grow on decomposing organic matter, such as rotting logs. Slime molds consume small organisms and organic matter.

figure 25-14

Slime molds often grow on decomposing organic matter, such as rotting logs. Slime molds consume small organisms and organic matter.

figure 25-15

Both plasmodial slime molds and cellular slime molds produce fruiting bodies that resemble those of fungi.

Both plasmodial slime molds and cellular slime molds produce fruiting bodies that resemble those of fungi.

figure 25-16

Some parasitic water molds attack aquatic organisms, such as fish, forming long filaments that eventually harm the fish.

Phylum Oomycota (Water Molds)

The phylum Oomycota (OH-mie-KOH-tuh) includes a number of organisms that are parasitic. For example, some oomycotes affect fish, as shown in Figure 25-16. Oomycotes reproduce asexually and sexually. During asexual reproduction, they produce flagellated zoospores. Zoospores germinate into threadlike cells. Some zoospores form a zoosporangium, which produces new zoospores. During sexual reproduction, water mold cells develop egg-containing and sperm-containing structures. Fertilization tubes grow between the two types of structures, enabling sperm to fertilize eggs, which forms diploid zygotes. A zygote grows into a new mass of filaments, which can again reproduce asexually or sexually.

Phylum Chytridiomycota (Water Molds)

Members of phylum Chytridiomycota (kie-TRID-ee-oh-mie-KOH-tuh), or the chytrids (KIE-tridz), are primarily aquatic protists characterized by gametes and zoospores with a single, posterior flagellum. Most chytrids are unicellular and parasitic.

Chytrids share many characteristics with fungi. They have similar means of obtaining nutrients, cell walls made of the same type of material, filamentous bodies, and similar enzymes and biochemical pathways. Because of these similarities, many biologists classify chytrids as fungi. Other biologists hypothesize that chytrids are a link between protists and fungi.

Comparing Funguslike Protists

Materials paper and pencil Procedure Create a chart that compares the phyla of funguslike protists. Include descriptions of cellular structure, locomotion, and means of reproduction. Analysis Which funguslike protists are haploid? Which are diploid? Which funguslike protists reproduce sexually? Which reproduce asexually?

Comparing Funguslike Protists

Materials paper and pencil Procedure Create a chart that compares the phyla of funguslike protists. Include descriptions of cellular structure, locomotion, and means of reproduction. Analysis Which funguslike protists are haploid? Which are diploid? Which funguslike protists reproduce sexually? Which reproduce asexually?

Was this article helpful?

0 0
Sirens Sleep Solution

Sirens Sleep Solution

Discover How To Sleep In Peace And Harmony In A World Full Of Uncertainty And Dramatically Improve Your Quality Of Life Today! Finally You Can Fully Equip Yourself With These “Must Have” Tools For Achieving Peace And Calmness And Live A Life Of Comfort That You Deserve!

Get My Free Ebook


Post a comment