Zoology 11101 Lecture 2 PDF

Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Lecture 2 TAXONOMY is the SCIENCE of CLASSIFICATION There are ma...

Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Lecture 2 TAXONOMY is the SCIENCE of CLASSIFICATION There are many different organisms. Scientists needed a method to name and group these organisms. th Carolus Linnaeus (Swedish scientist) was an 18 century scientist who invented a system called binomial nomenclature (two name system). Other scientists improved the system to include more categories (Kingdom, Phylum, Class, Order, Family..) Carolus Linnaeus is considered the father of taxonomy. Linnaeus used the Genus and species names. Example: Musca domestia* is the scientific name for house cat. *It is important to note that the Genus name (Musca) is written with an upper case letter and the species name (domestica) is written in all lower case letters. Modern scientists have developed seven different categories that we can use to name an organism. They are: Kingdom, Phylum, Class, Order, Family, Genus, and species. Taxonomy is the science of classifying organisms. The largest category is called the Kingdom, and this is broken down into a smaller group called a Phylum. Class is smaller than a Phylum, and so on. There are five major kingdoms used to classify living organisms:  Kingdom Animalia - These are made up of animals. Examples: Ants, frogs, horses, and humans  Kingdom Plantae – These are made up of plants which are organisms that can use photosynthesis to make their own food. Examples: Trees, grass, a cactus, and algae  Kingdom Fungi – These organisms feed on dead organisms. They also help to decay or decompose these organisms. Examples: Mushrooms, mold, and puffballs  Kingdom Protista – These are unicellular (one-celled) organisms and have a nucleus (prokaryotes). Some can make their own food and some cannot. Examples: Amoeba, Protists, and Euglena.  Kingdom Monera – These are unicellular organisms that do not have a nucleus (prokaryotes). Some can make their own food and some cannot. Examples: Eubacteria and Archaebacteria. All living things must be able to reproduce, grow, use energy, respond to their environment, and adapt to their environment. Zoology 11101 1 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE There are also some non-living things that can act like a living organism. These are not classified in the kingdoms of living organisms. Examples: Fire, virus* Note: *Even though a virus can reproduce inside a cell, it is not considered a living organism because it cannot reproduce on its own. The Kingdom Protista (Protists) The kingdom Protista contains many unicellular, colonial, and multicellular groups. Protists are the most diverse of the four kingdoms in the domain Eukaryota. Some can make their own food, but others do not. Some protists can move using cilia or flagella. Cilia and flagella are tail-like structures that protisits can use to swim. We must use a microscope to look at organisms in the kingdom protista because they are too small to see with just the eye. Concept Outline 1) Eukaryotes probably arose by endosymbiosis. (why?) Endosymbiosis. Mitochondria and chloroplasts are thought to have arisen by endosymbiosis from aerobic bacteria (How?). The theory of endosymbiosis proposes that aerobic eubacteria became mitochondria. Cyanobacteria became chloroplasts after being taken up by eukaryotic cells. Zoology 11101 2 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE 2) The kingdom Protista is by far the most diverse of any kingdom. (why?) General Biology of the Protists: Protista contains members exhibiting a wide range of methods of locomotion, nutrition, and reproduction. Protists are united on the basis of a single negative characteristic: they are not fungi, plants, or animals. In all other respects they are highly variable with no uniting features. Many are unicellular, but there are numerous colonial and multicellular groups. Most are microscopic, but some are as large as trees. The Cell Surface: Protists possess a varied array (group) of cell surfaces. Some protists, like amoebas, are surrounded only by their plasma membranes. All other protists have a plasma membrane but some, like algae and molds, are encased within strong cell walls. Still others, like diatoms and forams, secrete glassy shells of silica. Diatoms Forams Locomotor Organelles: Protists move principally by either flagellar rotation or pseudopodial movement. Many protists wave one or more flagella to propel themselves through the water, while others use flagella-like structures called cilia to create water currents for their feeding or propulsion. Pseudopodia are the chief means of locomotion among amoeba, whose pseudopods are large, extensions of the cell body called lobopodia. Other related protists extend thin, branching protrusions called filopodia. Other protists extend long, thin pseudopodia called axopodia supported by axial rods of microtubules. Cyst Formation Many protists with delicate surfaces are successful in quite harsh habitats. How do they manage to survive so well? They survive in hospitable conditions by forming cysts. A cyst is a dormant (still) form of a cell with a resistant outer covering in which cell metabolism is more or less completely shut down. Not all cysts are so sturdy (strong). Zoology 11101 3 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Nutrition Some protists are photosynthetic autotrophs and are called phototrophs. Others are heterotrophs that obtain energy from organic molecules synthesized by other organisms. Among heterotrophic protists, those that ingest visible particles of food are called phagotrophs, or holozoic feeders. Those ingesting food in soluble form are called osmotrophs, or saprozoic feeders. Phagotrophs ingest food particles into intracellular vesicles called food vacuoles or phagosomes. Lysosomes fuse with the food vacuoles, introducing enzymes that digest the food particles within. Reproduction Protists typically reproduce asexually, reproducing sexually only in times of stress. Asexual reproduction includes mitosis, but the process is often somewhat different from the mitosis that occurs in multicellular animals. In some groups, asexual reproduction involves spore formation, in others fission. The most common type of fission is binary, in which a cell simply splits into nearly equal halves. When the progeny cell is considerably smaller than its parent, and then grows to adult size, the fission is called budding. In multiple fission, or schizogony, common among some protists, fission is preceded by several nuclear divisions, so that fission produces several individuals almost simultaneously. Sexual reproduction also takes place in many forms among the protists. In ciliates and some flagellates, gametic meiosis occurs just before gamete formation, as it does in metazoans. In the sporozoans, zygotic meiosis occurs directly after fertilization, and all the individuals that are produced are haploid until the next zygote is formed. 3) Protists can be categorized into five groups (Five Groups of Protists) The protists are divided into five general groups according to some of the major shared characteristics. These are characteristics: (1) The presence or absence and type of cilia or flagella. (2) The presence and kinds of pigments (3) The type of mitosis (4) The kinds of cristae present in the mitochondria. (5) The molecular genetics of the ribosomal “S” subunit (6) Overall body form (amoeboid, coccoid, and so forth) (8) The protest has any kind of shell or other body “armor,” and (9) Modes of nutrition and movement. The protists are divided into five general groups: Heterotrophs with No Permanent Locomotor Apparatus. Amoebas and other sarcodines have no permanent locomotor apparatus. Photosynthetic Protists. The flagellates are photosynthesizers that propel themselves through the water with flagella. Diatoms are photosynthesizers with hard shells of silica. Algae are photosynthetic protists, some are multicellular. Zoology 11101 4 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Heterotrophs with Flagella. Flagellates induce themselves through the water. Single cells with many cilia, the ciliates possess highly complex and specialized organelles. Non-motile Spore-Formers. The sporozoans are nonmotile parasites that spread by forming spores. Heterotrophs with Restricted Mobility. Heterotrophs with restricted (limited) mobility, molds have cell walls made of carbohydrate. Group No 1: Heterotrophs with No Permanent Locomotor Apparatus The largest of the five general groups of protists are primarily unicellular organisms with amoeboid forms. There are three principle phyla: the forms and the radiolarians have carbonate shells and the rhizopods lack shells. Zoology 11101 5 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Rhizopoda: The Amoebas Hundreds of species of amoebas are found throughout the world in both fresh and salt waters. They are also numerous in soil. Many kinds of amoebas are parasites of animals. Reproduction in amoebas occurs by fission, or the direct division into two cells of equal volume. Amoebas of the phylum Rhizopoda lack cell walls, flagella, meiosis, and any form of sexuality. They do undergo mitosis, with a spindle apparatus that resembles that of other eukaryotes. Amoebas move from place to place by means of their pseudopods. An amoeba puts a pseudopod forward and then flows into it. Microfilaments of actin and myosin similar to those found in muscles are associated with these movements. Some kinds of amoebas form resistant cysts. In parasitic species such as Entamoeba histolytica, which causes amoebic dysentery, cysts enable the amoebas to resist digestion by their animal hosts. The primary infection takes place in the intestine, but it often moves into the liver and other parts of the body. The cysts are dispersed in the feces and may be transmitted from person to person in infected food or water, or by flies. It is estimated that up to 10 million people in the United States have infections of parasitic amoebas. Group No 2: Photosynthetic Protists Euglenophyta: The Euglenoids Most of the approximately 1000 known species of euglenoids live in fresh water. About a third of the approximately 40 genera of euglenoids have chloroplasts and are fully autotrophic; the others lack chloroplasts, ingest their food, and are heterotrophic. These organisms are not significantly different from some groups of zoomastigotes. Some euglenoids with chloroplasts may become heterotrophic if the organisms are kept in the dark; the chloroplasts become small and nonfunctional. If they are put back in the light, they may become green within a few hours. Normally photosynthetic euglenoids may sometimes feed on dissolved or particulate food. Zoology 11101 6 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Individual euglenoids range from 10 to 500 micrometers long and are highly variable in form. Interlocking proteinaceous strips arranged in a helical pattern form a flexible structure called the pellicle, which lies within the cell membrane of the euglenoids. Because its pellicle is flexible, a euglenoid is able to change its shape. Reproduction in this phylum occurs by mitotic cell division. The nuclear envelope remains intact throughout the process of mitosis. No sexual reproduction is known to occur in this group. In Euglena, the genus for which the phylum is named, two flagella are attached at the base of a flask-shaped opening called the reservoir, which is located at the anterior end of the cell. One of the flagella is long and has a row of very fine, short, hair-like along one side. A second, shorter flagellum is located within the reservoir but does not emerge from it. Contractile vacuoles collect excess water from all parts of the organism and empty it into the reservoir, which apparently helps regulate the osmotic pressure within the organism. The stigma, an organ that also occurs in the green algae (phylum Chlorophyta), is light-sensitive and aids these photosynthetic organisms to move toward light. Cells of Euglena contain numerous small chloroplasts. These chloroplasts, like those of the green algae and plants. Group No 3: Heterotrophs with Flagella The phylum Sarcomastigophora contains a diverse group of protists combined into one phylum because they all possess a single kind of nucleus and use flagella or pseudopodia (or both) for locomotion. We will focus on the class Zoomastigophora. Zoomastigophora: The Zoomastigotes The class Zoomastigophora is composed of unicellular, heterotrophic organisms that are highly variable in form. Each has at least one flagellum, with some species having thousands. They include both freeliving and parasitic organisms. Many zoomastigotes apparently reproduce only asexually, but sexual reproduction occurs in some species. The members of one order, the kinetoplastids, include the genera Trypanosoma and Crithidia, pathogens of humans and domestic animals. Zoology 11101 7 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Trypanosomes cause many serious human diseases, the most familiar of which is trypanosomiasis also known as African sleeping sickness. Trypanosomes cause many other diseases including East Coast fever, leishmaniasis, and Chagas’ disease, all of great importance in tropical areas where they afflict millions of people each year. Leishmaniasis, which is transmitted by sand flies, afflicts about 4 million people a year. The effects of these diseases range from extreme fatigue and lethargy in sleeping sickness to skin sores and deep eroding lesions that can almost obliterate the face in leishmaniasis. The trypanosomes that cause these diseases are spread by piercing-sucking insects, including tsetse flies and assassin bugs. A serious effort is now under way to produce a vaccine for trypanosome caused diseases. These diseases make it impossible to raise domestic cattle for meat or milk in a large portion of Africa. For example, tsetse fly-transmitted trypanosomes have evolved an elaborate genetic mechanism for repeatedly changing the antigenic nature of their protective glycoprotein coat, thus dodging the antibodies their hosts produce against them. Only a single one out of some 1000 to 2000 variable antigen genes is expressed at a time. When the trypanosomes are ingested by a tsetse fly, they go up on a complicated cycle of development and multiplication, first in the fly’s gut and later in its salivary glands. It is their position in the salivary glands that allows them to move into their vertebrate host. Recombination has been observed between different strains of trypanosomes introduced into a single fly, thus suggesting that mating, syngamy, and meiosis occur, even though they have not been observed directly. Although most trypanosome reproductionis asexual, this sexual cycle, reported for the first time in 1986, affords still further possibilities for recombination in these organisms. In the guts of the flies that spread them, trypanosomes are non-infective. Zoology 11101 8 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE When they are ready to transfer to the skin or bloodstream of their host, trypanosomes migrate to the salivary glands and acquire the thick coat of glycoprotein antigens that protect them from the host’s antibodies. When they are taken up by a fly, the trypanosomes again shed their coats. The production of vaccines against such a system is complex, but tests are underway. Releasing sterilized flies to impede the reproduction of populations is another technique used to try to control the fly population. Traps made of dark cloth and scented like cows, but poisoned with insecticides, have likewise proved effective. Research is proceeding rapidly because the presence of tsetse flies with their associated trypanosomes blocks the use of some 11 million square kilometers of potential grazing land in Africa. Group No 3 (cont.): Ciliophora: The Ciliates As the name indicates, most members of the Ciliophora feature large numbers of cilia. These heterotrophic, unicellular protists range in size from 10 to 3000 micrometers long. About 8000 species have been named. Despite their unicellularity, ciliates are extremely complex organisms, inspiring some biologists to consider them organisms without cell boundaries rather than single cells. Their most characteristic feature, cilia, are usually arranged either in longitudinal rows or in spirals around the body of the organism. In some groups, the cilia have specialized locomotory and feeding functions, becoming fused into sheets, spikes, and rods which may then function as mouths, paddles, teeth, or feet. The ciliates have a tough but flexible outer covering called the pellicle that enables the organism to squeeze through or move around many kinds of obstacles. All ciliates that have been studied have two very different types of nuclei within their cells, small micronuclei and larger macronuclei. The micronuclei, which contain apparently normal diploid chromosomes, divide by meiosis and are able to undergo genetic recombination. Macronuclei are derived from certain micronuclei in a complex series of steps. Within the macronuclei are multiple copies of the genome, and the DNA is divided into small pieces smaller than individual chromosomes. Ciliates form vacuoles for ingesting food and regulating their water balance. Food first enters the gullet, which in the well-known ciliate Paramecium is lined with cilia fused into a membrane. From the gullet, the food passes into food vacuoles, where enzymes and hydrochloric acid aid in its digestion. After the digested material has been completely absorbed, the vacuole empties its waste contents through a special pore in the pellicle known as the cytoproct. The cytoproct is essentially an exocytotic vesicle that appears periodically when solid particles are ready to be expelled. The contractile vacuoles, which function in the regulation of water balance, periodically expand and contract as they empty their contents to the outside of the organism. Ciliates usually reproduce by transverse fission of the parent cell across its short axis, thus forming two identical Zoology 11101 9 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE individuals. In this process of cell division, the mitosis of the micronuclei proceeds normally, and the macronuclei divide as just described. In Paramecium, the cells divide asexually for about 700 generations and then die if sexual reproduction has not occurred. Like most ciliates, Paramecium has a sexual process called conjugation, in which two individual cells remain attached to each other for up to several hours. Only cells of two different genetically determined mating types, odd and even, are able to conjugate. Meiosis in the micronuclei of each individual produces several haploid micronuclei, and the two partners exchange a pair of these micronuclei through a cytoplasmic bridge that appears between the two partners. In each conjugating individual, the new micronucleus fuses with one of the micronuclei already present in that individual, resulting in the production of a new diploid micronucleus in each individual. After conjugation, the macronucleus in each cell disintegrates, while the new diploid micronucleus undergoes mitosis, thus giving rise to two new identical diploid micronuclei within each individual. One of these micronuclei becomes the precursor of the future micronuclei of that cell, while the other micronucleus undergoes multiple rounds of DNA replication, becoming the new macronucleus. This kind of complete segregation of the genetic material is a unique feature of the ciliates and makes them ideal organisms for the study of certain aspects of genetics. Progeny from a sexual division in Paramecium must go through about 50 asexual divisions before they are able to conjugate. Zoology 11101 10 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Zoology 11101 11 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Notes: The zoomastigotes are a highly diverse group of flagellated unicellular heterotrophs, containing among their members the ancestors of animals as well as the very primitive Giardia. Ciliates possess characteristic cilia, and have two types of nuclei. The macronuclei contain multiple copies of certain genes, while the micronuclei contain multigene chromosomes. Group No 4: Nonmotile Spore-Formers Apicomplexa: The Sporozoans All sporozoans are nonmotile, sporeforming parasites of animals. Their spores are small, infective bodies that are transmitted from host to host. These organisms are distinguished by a unique arrangement of fibrils, microtubules, vacuoles, and other cell organelles at one end of the cell. There are 3900 described species of this phylum; best known among them is the malarial parasite, Plasmodium. Sporozoans have complex life cycles that involve both asexual and sexual phases. Sexual reproduction involves an alternation of haploid and diploid generations. Both haploid and diploid individuals can also divide rapidly by mitosis, thus producing a large number of small infective individuals. Sexual reproduction involves the fertilization of a large female gamete by a small, flagellated male gamete. The zygote that results soon becomes an oocyst. Within the oocyst, meiotic divisions produce infective haploid spores called sporozoites. An alternation between different hosts often occurs in the life cycles of sporozoans. Sporozoans of the genus Plasmodium are spread from person to person by mosquitoes of the genus Anopheles ; at least 65 different species of this genus are involved. When an Anopheles mosquito penetrates human skin to obtain blood, it injects saliva mixed with an anticoagulant. If the mosquito is infected with Plasmodium, it will also inject the elongated sporozoites into the bloodstream of its victim. The parasite makes its way through the bloodstream to the liver, where it rapidly divides asexually. After this division phase, merozoites, the next stage of the life cycle, form, either reinvading other liver cells or entering the host’s bloodstream. In the bloodstream, they invade the red blood cells, dividing rapidly within them and causing them to become enlarged and ultimately to rupture. This event releases toxic substances throughout the body of the host, bringing about the well-known cycle of fever and chills that is characteristic of malaria. The cycle repeats itself regularly every 48 hours, 72 hours, or longer. Zoology 11101 12 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Plasmodium enters a sexual phase when some merozoites develop into gametocytes, cells capable of producing gametes. There are two types of gametocytes: male and female. Gametocytes are incapable of producing gametes within their human hosts and do so only when they are extracted from an infected human by a mosquito. Within the gut of the mosquito, the male and female gametocytes form sperm and eggs, respectively. Zygotes develop within the mosquito’s intestinal walls and ultimately differentiate into oocysts. Within the oocysts, repeated mitotic divisions take place, producing large numbers of sporozoites. These sporozoites migrate to the salivary glands of the mosquito, and from there they are injected by the mosquito into the bloodstream of a human, thus starting the life cycle of the parasite again. Malaria. Malaria, caused by infections by the sporozoan Plasmodium, is one of the most serious diseases in the world. According to the World Health Organization, about 500 million people are affected by it at any one time, and approximately 2 million of them, mostly children, die each year. The symptoms, familiar throughout the tropics, include severe chills, fever, and sweating, an enlarged and tender spleen, confusion, and great thirst. Ultimately, a victim of malaria may die of anemia, kidney failure, or brain damage. The disease may be brought under control by the person’s immune system or by drugs. As discussed in chapter 21, some individuals are genetically resistant to malaria. Other persons develop immunity to it. Efforts to eradicate malaria have focused on (1) the elimination of the mosquito vectors; (2) the development of drugs to poison the parasites once they have entered the human body; and (3) the development of vaccines. Notes: The best known of the sporozoans is the malarial parasite Plasmodium. Like other sporozoans, Plasmodium has a complex life cycle involving sexual and asexual phases and alternation between different hosts, in this case mosquitoes and humans. Malaria kills about 2 million people each year. Zoology 11101 13 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Zoology 11101 14 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Kinds of Protists Zoology 11101 15 Dr. Ahmed M. EL-SABROUT