Lecture 3 Protists Discussion PDF
Document Details
Uploaded by PromisedScandium
Tags
Summary
This document is a lecture on the topic of protists, focusing on their life cycles. It discusses the two-host life cycle of Plasmodium, the organism that causes malaria, as well as the life cycles of slime molds, including plasmodial slime molds and Dictyostelium.
Full Transcript
Lecture 3 Protists Details on life cycles seen in the class The Two-Host Life Cycle of Plasmodium, the Apicomplexan that Causes Malaria Figure 28.17 The two-host life cycle of Plasmodium, the apicomplexan that causes malaria. The Two-Host Life Cycle of Plasmodium, the Apicomplexan th...
Lecture 3 Protists Details on life cycles seen in the class The Two-Host Life Cycle of Plasmodium, the Apicomplexan that Causes Malaria Figure 28.17 The two-host life cycle of Plasmodium, the apicomplexan that causes malaria. The Two-Host Life Cycle of Plasmodium, the Apicomplexan that Causes Malaria 1. An infected Anopheles mosquito bites a person, injecting Plasmodium sporozoites (haploid) in its saliva. 2. The sporozoites enter the person’s liver cells. After several days, the sporozoites undergo multiple divisions and become merozoites, which use their apical complex to penetrate red blood cells. 3. The merozoites divide asexually inside the red blood cells. At intervals of 48 or 72 hours (depending on the species), large numbers of merozoites break out of the blood cells, causing periodic chills and fever. Some of the merozoites infect other red blood cells. 4. Some merozoites form gametocytes (haploid). 5. Another Anopheles mosquito bites the infected person and picks up Plasmodium gametocytes along with blood. 6. Gametes (haploid) form from gametocytes; each male gametocyte produces several slender male gametes. Female gametes are also formed. 7. Fertilization occurs in the mosquito’s digestive tract, and a diploid zygote forms. 8. Following meiosis, an oocyst (haploid) develops from the zygote in the wall of the mosquito’s gut. The oocyst releases thousands of haploid sporozoites, which migrate to the mosquito’s salivary gland. The life cycle of a plasmodial slime mold Figure 28.26 The life cycle of a plasmodial slime mould. The life cycle of a plasmodial slime mold The life cycle diagram of plasmodial slime mould highlights fertilization, meiosis, and haploid and diploid stages, as follows: In the feeding stage, the cells form a slug-like aggregate and get ready to mature. The feeding stage is a multinucleate plasmodium. The mature plasmodium form webbings and prepare to fruit by forming young sporangium that resembles a conical mass. The diploid plasmodium erects stalked fruiting bodies (sporangia) when conditions become harsh. The sporangium matures to form a circular ball supported by a stalk. The ball has many spores inside it. As the sporangium undergoes meiosis, a coat develops over the spores. In the sporangia, meiosis produces haploid spores, which disperse through the air. Germinating spores releases motile cells. The resistant haploid spores germinate in favourable conditions, releasing haploid motile cells. Haploid flagellated cells and haploid amoeboid cells are formed. The motile haploid cells are either amoeboid or flagellated; the two forms readily convert from one to the other. 6. During fertilization, the motile cells fuse, forming diploid zygotes. 7. Repeated mitotic divisions of the diploid zygote’s nucleus, without cytoplasmic division, form the plasmodium. The life cycle of Dictyostelium, a cellular slime mold Figure 28.27 The life cycle of Dictyostelium, a cellular slime mould. The life cycle of Dictyostelium, a cellular slime mold 1. In the feeding stage, solitary haploid amoebas (cells with lobe-like extensions) engulf bacteria; these solitary cells periodically divide by mitosis (asexual reproduction). 2. During sexual reproduction, two haploid amoebas fuse and form a diploid zygote. 3. The diploid zygote becomes a giant cell by consuming haploid amoebas. After developing a resistant wall, the giant cell undergoes meiosis followed by several mitotic divisions. 4. The wall ruptures, releasing new haploid amoebas. 5. When food is depleted, hundreds of amoebas congregate in response to a chemical attractant and form a haploid slug-like aggregate. A photo shows slug-like form at a scale of 200 micrometres. 6. The haploid aggregate migrates for a while and then stops. Some of the cells dry up after forming a stalk that supports a haploid asexual fruiting body. 7. Other cells crawl up the stalk of the haploid fruiting bodies and develop into haploid spores. 8. Haploid spores are released from the fruiting bodies. 9. In favourable conditions, haploid amoebas emerge from the spore coats and feed, and the cycle can begin again.