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Biology (Biological Sciences)
Richard Moses

Topic 5 Monday, February-23-09: • Last time: o Finished key events: the invasion of land and continental drift o Begin topic 5, the Protists o Protist characteristics o Supergroup Excavata • Today o Supergroup Chromalveolata  Dinoflagellates  Plasmodium, malaria, and sickle cell anemia o Introduction to protist life cycles • Midterm Test worth 15% of mark o Friday, February 27, 2009-02-23 50 minutes o 20-25 multiple choice o 5-10 true or false o 2-3 written (worth about 15% of total) o Covers material from start of semester o Covers material including Wednesday’s class • Phylogeny of the “Protists” – figure 28.3 • Excavata – seem to be missing mitochondria o Actually have degraded or secondarily modified mitochondria or organelles that stemmed from mitochondria Supergroup: Chromaveolata • Though to be united by secondary endosymbiosis with ancestral red algae? o See figure 28.2 • Most are photosynthetic and thought to get their plastids from red algae o Though to have multiple membranes around their chloroplasts o This is due to secondary endosymbiosis where a bigger cell engulfs a red algae, which had previously engulfed a chloroplast o Asynapomorphic trait is the secondary endosymbiosis of chloroplasts and red algae • Alveolata: membrane-bound alveoli – all chromaveolata have these – synapomorphic trait • Dinoflagellata: the dinoflagellates o Most are photosynthetic (algae) o Most are maring and unicellular o Armour of cellulose plates o Important component of phytoplankton with diatoms (stramenopilan chromaveolates)  Phytoplankton floats around on their own o Many are bioluminescent  Do this to attract the predators of their predators  Then the predators that are eating the dinoflagellates get eaten by their predators  The “burglar” hypothesis o Many are symbionts  E.g. Coral reefs  o Many dinoflagellates exhibit population explosions  E.g. “red tides” (red from xanthophylls) • Dinoflagellates that go crazy with their growth • E.g. Pfiesteria • Massive fish kills from neurotoxins secreted by the dinaflagellates occur • Responds to anthropogenic nutrient loading (“eutrification”) o Put a lot of nutrients into a water system causing the dinoflagellates to grow excessively • In Science May and December 2007 o Global temperatures are increasing, and thus the water is getting too warm for the dinaflagellates to photosynthesize and thus the symbiotic relationship that creates coral reefs cannot function properly o Called the “bleaching” of coral reefs • In Nature 2004 o Corals’adaptive response to climate change o “increased seawater temperature cause corals to lose their symbiotic algae” o “Some corals have adapted to higher temperatures by hosting high temperature- adapted Symbiodinium” • Apicomplexans – sister group to Dinoflagellagtes o But are not photosynthetic o Have “apicoplasts”  remnany of red aldal chloroplast? o In Science Feb 2008  Aphotosynthetic alveolate closely related to apicomplexan parasites o New species sister toApicomplexans but with photosynthetic plastid o Are all parasites o Terminal apex for penetrating host o Complex life cycles with > 1 host o Part of that life cycle involves sexual reproduction, and part involves asexual reproduction • E.g. Plasmodium  malaria o Requires 2 hosts for its life cycle: mosquito and humans o Malaria – dominates in tropical areas where mosquitoes live  1.5 million deaths/year  most are children • Equivalent to 10 Boeing 747s full of children crashing every day of the year  Incidence of malaria is increasing worldwide o Plasmodium Life Cycle – Figure 28.10 The two-host life cycle of Plasmodium, the apicomplexan that causes malaria  Throughout the textbook the blue arrows represent the haploid lifecycle  The brown arrows represent the diploid life cycle  Mosquito lands on your arm and it is infected with plasmodium  The sporozoites (haploid) from the plasmodium oocyst are in the salivary gland  They then go trhoguh the human bloodstream and then enter your liver  They go thorugh asexual reproduction in the liver and mature into merozoites (haploid) • When they become the merozoites they can then burrow into your red blood cells  The merozoites asexually reproduce in the RBC’s and then break free as the gametocytes (haploid)  The gametocytes develop and become gametes (haploid stages that are going to go through fertilization)  The male and female gametes get fertilized inside a female mosquito  The zygote (diploid) is then formed and immediately goes through meiosis  When they go through meiosis they form an oocyst, and eventually burst releasing sporozoites (haploid) o The plasmodium life cycle is mostly haploid and asexual o Zygote  in mosquito  Quick meiosis “zygotic meiosis” o Massive mitotic division in RBC’s cause fever in humans • Sickle CellAnaemia and Malaria in Humans – related to a simple genetic mutation o Sickle CellAnemia results from a simple genetic mutation (1 amino acid substitution in haemoglobin” o Homozygotes are severely affected and cannot take in as much oxygen o The allele persists because the people who are heterozygotes for the sickle-cell anaemia allele are resistant to malaria  You have some normal RBC’s and some sickle cell RBC’s o Natural selection actually causes the retention of an allele that causes disease and death in some individuals • Remember that protists are a very diverse group o All the other eukaryotes that we know of (plants, fungi and animals) all come from protists ancestor o Arch Wednesday, February 25, 2009 • Figure 28.2 is supposed to show how secondary endosymbiosis occurs with red and green algae o Primary endosymbiotic event occurs when a heterotrophic eukaryote engulfs a cyanobacterium o Then there is differentiation into red algae and green algae o Then secondary endosymbiosis occurs when the red algae and the green algae are engulfed by larger eukaryotes o The whole Chromalveolata clade inherited the photosynthetic ability from red algae  Alarge eukaryote engulfed red algae t form the chromalveolata  Some Chromalveolata lost their photosynthetic abilities o The green algae was engulfed by the Euglenids and the Chlorarachniophytes Protist Sexual Life Cycles: • There are three types of life cycles in eukaryotes (Figure 13.6) o Seen in animals – mostly diploid and a small haploid part o Plants and some algae – about half and half for diploid and haploid o Most fungi and some protists – mostly haploid and a small diploid part • Which stage is multicellular (or dominant)? Hapoid or Diploid? o 1. Haploid is multicellular and/or dominant  “haplontic” or “zygotic meiosis” – the zygote goes through meiosis  The fertilization and diploidy stage doesn’t last very long  Haploid stage is dominant  Only on cell type (zygote) is diploid  Examples • Plasmodium • Chlamydomonas (unicellular green algae) • Cellular slime molds (Dictyostelida) • All fungi  Figure 13.6 c o 2. Haploid and Diploid are both multicellular (Figure 13.6 b)  Both the haploid stage and the diploid stage have multicellular stages from mitosis  “alternation of generations” and “sporic meiosis” • The products of meiosis are spores • The spore goes through mitotic division to produce something multicellular o Sporophyte (2n) goes through meiosis producing spores o Haploid cells produced through meiosis o Divide mitotically to produce multicellular gametophyte o Do not fuse with other cells like gametes do • The gamete fuses with another gamete to go through sexual reproduction forming a zygote o Gametophyte produces gametes • Diploid stage is sporophyte • Haploid stage is gametophyte • All plants that we know of have alternation of generations • Alternation of generat
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