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Chapter 29

Chapter 29- Protists.docx

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University of Toronto Mississauga
Fiona Rawle

Chapter 29 – Protists -paraphyletic group- they represent some, but not all, of the descendents of a single common ancestor. - Protists are all eukaryotes that are not green plants, animals or fungi. 29.1 Why Do Biologists Study Protists? Impacts on Human Health and Welfare Malaria: Caused byApicomplexa. World’s most chronic health problem. Four species of the protist Plasmodium are capable of parasitizing humans and causing malaria. Plasmodium spends part of its life cycle inside mosquitoes; most antimalaria campaigns have focused on controlling these insects. HarmfulAlgal Blooms: Due to photosynthetic protists called dinoflagellates. Harmful at high population density because synthesize toxins to protect themselves from predation. Blooms known as red tides Ecological Importance of Protists -10 percent of euks Protists Play a Key Role inAquatic Food Chains Plankton: small organisms that live near the surface of oceans or lakes and that drift along or swim only short distances -Sugars and organic compounds produced by phytoplankton are the basis of food chains in freshwater and marine environments. Could Protists Help Reduce Global Warming? Global carbon cycle: Movement of carbon atoms from CO2 molecules in the atmosphere to organisms in the soil or ocean, and then back to atmosphere. -Phytoplankton die and sink to bottom of ocean: 1. Limestone and other carbon-containing rocks that form on the ocean floor can lock up carbon atoms. 2. Dead bacteria, archaea, protists accumulate at bottom of the ocean. C2 then passes from the atmosphere to the body of a photosynthetic protest and then to petroleum is removed from the atmosphere. 29.2 How Do Biologists Study Protists? Microscopy: Studying Cell Structure - Detailed studies of cell structure revealed that protists could be grouped according to characteristic overall form, according to organelles with distinctive features or both. - Synapomorphies: shared, derived traits that distinguish major monophyletic groups. Evaluating Molecular Phylogenies: Discovering New Lineages via Direct Sequencing 29.3 What Themes Occur in the Diversification of Protists? What Morphological Innovations Evolved in Protists? The Nuclear Envelope: Derived from infoldings of plasma membrane Evolution of envelope advantageous because it separated transcription and translation. Early morphological innovation gave early euks a new way to manage and process genetic info. Mitochondrion: Endosymbiosis theory: Mitochondria originated when a bacterial cell took up residence inside a eukaryote -Euk cells started to use their cytoskeletal elements to surround and engulf smaller prey. Instead of being digested, an engulfed bacterium began to live inside its euk host. Engulfed cell survived by absorbing carbon with high potential energy from host and oxidizing it using oxygen as final electron acceptor. Host supplied bacterium with protection from its other prey and carbon compounds, while bacterium produced much more ATP than host cell could. Following points support endosymbiosis theory: 1. Mitochondria are size of avg bacterium and replicate by fission like them. Duplication takes place independently of division by host cell. 2. Mitochondria have their own ribosomes and manufacture their own proteins. Ribosomes closely resemble bacterial ones in size and composition and are poisoned by antibiotics. 3. Double membranes, consistent with the engulfing mechanism of origin 4. Have their own genomes which are organized as circular molecules – much like a bacterial chromosome. 5. Mitochondrial gene sequences turned out to be much more closely related to the sequences from the a-proteobacteria than nuclear DNAof euks. Structures for Support and Protection - Diatoms surrounded by silicon-oxide shell - Dinoflagellates have a cell wall make of cellulose plates - Some lineages of Foraminifera secrete an intricate chambered test (hard external structure) of calcium carbonate - The parabasalids have a distinctive internal support rod, consisting of cross-linked microtubules - The euglenids have a collection of protein strips located under plasma membrane. Strips supported by microtubules and stiffen the cell - The alveolates have distinctive sac-like structures alveoli, under membrane that stiffen it. Multicellularity - Is a synapomorphy shared by all of brown algae and all of plasmodial and cellular slime moulds. Also arose in some lineages of red algae. How Do Protists Find Food? Ingestive Feeding: - The engulfing process is possible in protists that lack a cell wall - Flexible membrane and dynamic cytoskeleton gives these species the ability to swallow prey using pseudopodia. Absorptive Feeding - When nutrients are taken up directly from environment across plasma membrane -
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