Ch 23 Protists.docx

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University of Toronto Scarborough
Biological Sciences
Ivana Stehlik

Ch 23 Protists 23.1 Evolution of Protists Involved Endosymbiosis (Pg 498)  Evolved 1.5 to 2 billion years ago  Endosymbiosis played an important role. o Contain mitochondria and some contain chloroplasts o earliest eukaryotes acquired mitochondria by engulfing proteobacteria becoming heterotrophic eukaryotes  Chroloplast endosymbiosis o Cyanobacteria ingested by eukaryote that already had mitochondria. o Formed symbiotic relationship o Over evolutionary time, lost genes no longer required for independent existence and transferred most of its genes to the host’s nuclear genome.  Gave the host cell better control of overall cell function o Prokaryote became an organelle of an eukaryote o Some evolved this way, other: eukaryote engulfed a photosynthetic eukaryote that eventually became a chloroplast. 23.2 What is a Protist? Characteristics of Protists (Pg 499)  membrane-bound nucleus  multiple linear chromosomes  cytoplasmic organelles: mitochondria and chloroplast (in some species)  microtubules and microfilaments. o Provide motility and cytoskeletal support  characteristics of transcription and translation like eukaryotes  Phylogenetic relationship btw protists and eukaryotes is more complex. o Over evolutionary time, the eukaryotic family tree branched out in many directions o Plants, animals and fungi diverged from protest ancestors. o Some features similar, other distinctive.  Most protists are motile or have motile stages in their life cycle and their cell walls are made of cellulose o Fungi cell ways are made of chitin  Differences from plants: o Photoautotrophic protists can also live as heterotrophs  Some combine both modes of nutrition o Do not retain developing embryos in parental tissue o Do not have highly differentiated structures equivalent to roots, stems and leaves o Photosynthetic generally referred to as algae  Generally aquatic, unicellular and microscopic.  Many multicellular  Diff groups of algae are not closely related to each other.  Differences from animals: o Unlike protists, all animals are multicellular and have features such as an internal digestive tract and complex developmental stages o Protists lack nerve cells, highly differentiated structures such as limbs and a heart and collagen (extracellular support protein)  Animals in protest are not fungi, plants, animals or prokaryotes  Extremely diverse o Many were grouped into phyla under kingdom according to body form, nutrition modes and movement, forms of meiosis and mitosis. paraphyletic o Molecular data show that most protists do not share a common ancestor and the ones grouped together in a phyla are not closely related.  Some evolutionists believe that protista kingdom is collection of many kingdoms (as many as 30). 23.3 Protists’ Diversity is reflected in their metabolism, reproduction, structure and habitat (Pg 500)  Habitat o Live in aqueous habitats  Aquatic or moist terrestrial locations  Oceans, freshwater lakes, ponds, streams and moist soils and within host organisms  Saltwaters  extreme habitats (high/low pH, high/low salt, high/low temperature, high/low nutrients)  aerial habitats  Phytoplankton: in bodies of water, small photosynthetic protists collectively make up this  Capture light energy  Provide organic substance and oxygen for heterotrophic bacteria, other protists and animal larvae  Combined with large multicellular protists forming seaweeds, they account for half of the total organic matter produced by photosynthesis  Zooplankton: animal larvae that feed of phytoplankton  In moist soilds of terrestrial environments, protists play important roles among the detritus feeders that recycle matter from organic back to inorganic form  Enormously important in world ecosystems  Protists that live in host organisms are parasites, obtaining nutrients from the host.  Many human parasites are protists causing diseases such as malaria, sleeping sickness and amoebic dysentery.  Structure o Most single cells o Other live as colonies in which individual cells show little or no differentiation and are potentially independent.  Within colonies, individuals use cell signaling to cooperate on tasks such as feeding or movement. o Some are large multicellular organisms: giant kelp of coastal waters can rival forest trees in size. o Many single celled and colonial protists have complex intracellular structures  Reflect key aspects of habitats in which they live.  Fresh water protists.  Cytoplasm is hypertonic, water flows in.  Contractile vacuole gradually fills with fluid, when it reaches its maximum size, it moves to the plasma membrane and forcible contracts, expelling the fluid to the outside through a pore in the membrane. o Some are supported by an external cell wall or by an internal or external shell built up from organic or mineral matter o Instead of cell wall, other protists have a pellicle: a layer of supportive protein fibers located inside the cell just under the plasma membrane, providing strength and flexibility o Almost all protists move sometime during their lives.  Some move by amoeboid motion  Cell extends one or more lobes of cytoplasm called pseudopodia.  Rest of cytoplasm and nucleus then flow into the pseudopodium, completing the movement.  Other move by beating of the flagella or cilia.  Some protists: cilia are arranged in complex patterns, with an equally complex network of microtubules and other cytoskel
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