Protists

Chapter 27 Opening Roadmap. © 2017 Pearson Education, Inc.

Protists All eukaryotes except land plants, fungi, and animals Figure 27.1 Protists All eukaryotes except land plants, fungi, and animals Tend to live in environments where they are surrounded by water most of the time Open ocean: Surface waters teem with microscopic protists, such as these diatoms. Shallow coastal waters: Gigantic protists, such as these kelp, form underwater forests. Intertidal habitats: Protists such as these brown algae are particularly abundant in tidal habitats. Figure 27.1 Protists Are Particularly Abundant in Aquatic Environments. 1 mm © 2017 Pearson Education, Inc.

Impacts on Human Health and Welfare Several types of protists can cause human disease, and some also cause disease in our crops Irish potato famine of 1845: caused by the protist Phytophthora infestans Type of water mold Led to emigration, and mass starvation caused deaths

Malaria is one of the world’s most chronic public health problems Figure 27.2 Malaria is one of the world’s most chronic public health problems Five species of the parasitic protist Plasmodium transferred to humans from mosquitoes Haploid (n) Plasmodium cell type present in mosquito saliva that infects humans MITOSIS MITOSIS Diploid (2n) Mosquito bite (n) (n) Infection of liver cells in human Human host Figure 27.2 Plasmodium Lives in Mosquitoes and in Humans, Where It Causes Malaria. Mosquito host Infec tion o f gut w all in m o Male gametes (n) squito Plasmodium cell types present in human blood that infect mosquitoes MEIOSIS followed by MITOSIS Mosquito bite Zygote SYNGAMY (2n) Female gamete (n) © 2017 Pearson Education, Inc.

Table 27.1 Some Human Health Problems Caused by Protists. © 2017 Pearson Education, Inc.

Red tide: caused by photosynthetic dinoflagellates Figure 27.3 Shellfish filter-feed these organisms out of the water and are not harmed. Toxins accumulating in the shellfish poison animals including humans. 20 µm Figure 27.3 Harmful Algal Blooms Caused by Dinoflagellates. © 2017 Pearson Education, Inc.

CO2 Photosynthetic protists fix carbon from the atmosphere. Figure 27.4 CO2 Arrows indicate movement of carbon atoms Photosynthetic protists fix carbon from the atmosphere. Heterotrophic protists consume producers. All protists eventually die. Decomposers return carbon. But dead cells accumulate as a carbon reserve: limestone and/or fossil fuels. Primary producers Primary consumers Figure 27.4 Protists Play a Key Role in the Marine Carbon Cycle. Decomposers and scavengers Sinking Sinking Sinking Dead cells and CaCO3 shells accumulate on bottom © 2017 Pearson Education, Inc.

Flagellum Hairs on flagellum Branches on hairs 1 µm Table 27.2 Table 27.2 Distinguishing Features (Synapomorphies) of Major Lineages of Eukaryotes. © 2017 Pearson Education, Inc.

Most are unicellular, most are aquatic. Figure 27.6 Protista, a kingdom, was established in the 1900s – to contain organisms difficult to place. Most are unicellular, most are aquatic. Can be thought of as polyphyletic, or as monophyletic with nested kingdoms. Bacteria The Amoebozoa and Opisthokonta form the monophyletic group Unikonta (one tailed) Archaea AMOEBOZOA Lobose amoebae Cellular slime molds UNIKONTA Plasmodial slime molds OPISTHOKONTA Fungi Choanoflagellates All eukaryotes are protists except for the fungi, animals, and land plants Animals EXCAVATA Parabasalids EUKARYOTES Diplomonads Euglenids Kinetoplastids PLANTAE The other five major lineages form the monophyletic group Bikonta (two tailed) Glaucophyte algae Red algae Green algae Green plants Land plants BIKONTA Figure 27.6 Phylogenetic Analyses Have Identified Seven Major Lineages of Eukaryotes. RHIZARIA Actinopods Foraminiferans Chlorarachniophytes ALVEOLATA Ciliates Dinoflagellates Apicomplexans STRAMENOPILA Water molds Diatoms Brown algae © 2017 Pearson Education, Inc.

Related to muscle movement in animals Figure 27.14 Amoeboid motion is a sliding movement observed in some protists that is accomplished by streaming of pseudopodia Amoeboid motion via pseudopodia Chaos carolinensis Figure 27.14 Amoeboid Motion Is Possible in Species That Lack Cell Walls. 0.2 mm Requires ATP Related to muscle movement in animals Key immune system cells in humans use amoeboid motion © 2017 Pearson Education, Inc.

Flagella and cilia have identical structures, however: Figure 27.15 Flagella and cilia have identical structures, however: Flagella are long and are usually found alone or in pairs Cilia are short and numerous (a) Swimming via flagella (b) Swimming via cilia Figure 27.15 Many Protists Swim Using Flagella or Cilia. © 2017 Pearson Education, Inc.

Protists evolved the complementary processes: Figure 27.16a Protists evolved the complementary processes: mitosis, meiosis, and syngamy in their life cycles (a) A life cycle dominated by haploid cells (species shown here is the dinoflagellate Gyrodinium uncatenum) Haploid (n) Diploid (2n) SYNGAMY (n) Zygote (2n) Sexual reproduction (offspring produced by meiosis) Asexual reproduction (offspring produced by mitosis) Flagella 10 µm Fusing gamete pair Mature cell Figure 27.16a Life Cycles Vary Widely among Unicellular Protists. (n) (n) Gamete Gametes (n) (n) This is a unicellular life cycle which is dominated by populations of haploid cells with asexual reproduction © 2017 Pearson Education, Inc.

Other protists evolved the life cycle differently: Figure 27.16b Other protists evolved the life cycle differently: (b) A life cycle dominated by diploid cells (species shown here is the diatom Thalassiosira punctigera) In each division both halves become the external template of the daughter cells, therefore one of the daughter cells will be smaller Haploid (n) Diploid (2n) Zygote (2n) Initial cell Asexual reproduction (offspring produced by mitosis) Sexual reproduction (offspring produced by meiosis) 60 µm Mature cell (2n) Figure 27.16b Life Cycles Vary Widely among Unicellular Protists. Silicon dioxide cell wall Sperm MEIOSIS SYNGAMY (2n) Nucleus The smaller cells cannot divide any more and undergo sexual reproduction 20 µm Egg MEIOSIS Gametes (n) This is a unicellular life cycle which is dominated by populations of diploid cells with asexual reproduction © 2017 Pearson Education, Inc.

Figure 27.17a Yet other protists evolved with multicellular stages in their life cycles (a) Alternation of generations in which multicellular haploid and diploid forms look identical (Ectocarpus siliculosus) Male and female gametophytes are separate Meiosis occurs in specialized structures Spores (n) 100 µm Gametes are produced by mitosis in specialized structures Gametophytes 1 cm (n) Figure 27.17a Alternation of Generations Occurs in Many Multicellular Protists. Gametes Sporophyte (n) (2n) Egg Sperm Haploid (n) 50 µm Diploid (2n) SYNGAMY Zygote germinates and grows into sporophyte Zygote (2n) This is a diplohaplontic life cycle with multicellular diploid (sporophyte) and multicellular haploid (gametophyte) stages. © 2017 Pearson Education, Inc.

Table 27.3-1 Key Lineages of Protists. © 2017 Pearson Education, Inc.

Table 27.3-2 Key Lineages of Protists. © 2017 Pearson Education, Inc.