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BIO153H5 (147)
Chapter 29

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Christoph Richter

Chapter 29 NotesFundamental features that distinguish eukaryotes from bacteria and archaeaThe nuclear envelope is a synapomorphy that defines the EukaryaCompared to bacteria and archaea most eukaryotic cells are large have many more organelles and have much more extensive system of structural proteins called the cytoskeletonMulticellular is rare in bacteria and unknown in archaea but has evolved multiple times in eukaryotesBacteria and archaea reproduce asexually by fission many eukaryotes reproduce asexually via mitosisMany eukaryotes undergo meiosis and reproduce sexuallyThe term protist refers to all eukaryotes that are not land plants fungi or animals Protists are multicellular in both haploid and diploid phases of life cycleWhichprotistlineagecontainsorganismsthatalllackmitochondriaorchloroplastsExcavateProtists do not make a monophyletic group Instead they refer to a paraphyletic groupthey represent some but not all of the descendants of a single common ancestor No synapomorphies define the protists There is no trait found in protists that is not found in other organisms Protists tend to live in environments where they are surrounded by water 3 reasons why protists are studied1They are important medically2They are important ecologically3They are critical to understanding the evolution of plants fungi and animalsThree major infectious diseases currently affecting world1Tuberculosis2Human immunodeficiency virus HIV3MalariaTuberculosis is caused by a bacterium HIV is caused by a virusMalaria is caused by a protistspecifically by four species in the eukaryotic lineage called ApicomplexaMalaria ranks as the worlds most chronic public health problemFour species of the protist Plasmodium are capable of parasitizing humans Infections start when Plasmodium cells enter a persons bloodstream during a mosquito bite Plasmodium initially infects liver cell later some of the Plasmodium cells change into a distinctive cell type that infects the hosts red blood cells as well The Plasmodium cells multiply inside the host cells which are killed as parasite cells exit to infect additional liver cells or red blood cells If infected red blood cells are transferred to an Anopheles mosquito during a bite they differentiate to form gametes Inside the mosquito gametes fuse to form a diploid cell called an oocyst which undergoes meiosis The haploid cells that result from meiosis can infect a human when the mosquito bites again Although Plasmodium is arguably the best studied of all protists researchers have still not been able to devise effective and sustainable measures to control it Natural selection has favoured mosquito strains that are resistant to the insecticides that have been sprayed in their breeding habitats in attempts to control malarias spread Several species of Plasmodium have evolved resistance to most of the drugs used to control their growth in infected peopleEfforts to develop a vaccine against Plasmodium have been fruitless to date in part because the parasite evolves so quickly flu virus and HIV pose similar problemsWhen a unicellular species experiences rapid population growth and reaches high densities in an aquatic environment it is said to bloomHarmful algal blooms are usually due to photosynthetic protists called dinoflagellates Certain dinoflagellates synthesize toxins to protect themselves from predation by small animals called copepods Because toxinproducing dinoflagellates have high concentrations of accessory pigments called xanthophylls their blooms can sometimes discolour seawater producing the red tidesTABLE 291 ON PAGE 574Algal blooms can be harmful to people because clams and other shellfish filter photosynthetic protists out of water as food During a bloom high levels of toxins can build up in the flesh of these shellfish Typically the shellfish themselves are not harmed But if a person eats toxic shellfish several types of poisoning can resultParalytic shellfish poisoning occurs when people eat shellfish that have fed heavily on protists that synthesize poisons called saxitoxins Saxitoxins block ion channels that have to open for electrical signals to travel through nerve cells In humans high dosages of saxitoxins cause unpleasant symptoms such as prickling sensations in the mouth or even lifethreatening symptoms such as muscle weakness and paralysis
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