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 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. Learning Objectives Describe the habitats and life cycles of various protists. 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.
Life Cycle of Slime Molds Protist life cycles range from simple to extremely elaborate. Plasmodial slime molds The slime molds are categorized on the basis of their life cycles into plasmodial or cellular types. 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. Cellular slime molds The cellular slime molds function as independent amoeboid cells when nutrients are abundant. Still, in response to a chemicals signal, these individual cells aggregate, forming swarms.
Also, the multicellular slug, which forms as a result of this aggregation, is known as the pseudoplasmodia. Moreover, the uninucleate cell stage of the cellular slime molds is the haploid stage.
However, through the formation of the pseudoplasmodium , they enter into the asexual reproductive stage. Also, this pseudoplasmodium forms a stalked fruiting body in which spores are produced. Plasmodial or acellular slime molds refers to the slime molds enclosed within a single membrane without walls and is one large cell, while the cellular slime molds refer to the slime molds that exist in their vegetative form as uninucleate ameboid cells.
Plasmodial slime molds are bags of cytoplasm with thousands of individual nuclei, forming a multinucleate plasmodium form, while the cellular slime molds live most of their lives as unicellular protists. The somatic phase of plasmodial slime molds is diploid while the somatic phase of cellular slime molds is haploid. No aggregation occurs prior to the formation of sporangia in plasmodial slime molds while cellular slime molds aggregate, forming a pseudoplasmodium before the formation of sporangia.
The sporangium of plasmodial slime molds is covered by peridium while the sporangium of cellular slime molds is naked. Capitalum occurs inside the sporangium of plasmodial slime molds while capitalum is absent inside the sporangium of cellular slime molds. The spores germinate to produce flagellated gametes. These gametes fuse to form a diploid zygote. The zygote grows and its nucleus divides mitotically, but the cytoplasm does not divide, resulting in another plasmodium. Jekyll and Mr. SparkTeach Teacher's Handbook.
Summary Slime Molds. Previous section Problems Next section Problems. Take a Study Break.
0コメント