Eukaryotic Microorganisms and Parasites

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an organism that lives at the expense of another organism

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Parasite

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another organism, called the

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host

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Parasites that cause disease are called

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Pathogens

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study of parasites

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PARASITOLOGY

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refer to the study of protozoa, helminths, and arthropods that live at the expense of other organisms

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PARASITOLOGY

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such as ticks and lice, which live on the surface of other organisms

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Ectoparasites

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some protozoa and worms, which live within the bodies of other
organisms.

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Endoparasites

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spend at least
some of their life cycle in or on a host.
For example, the protozoan that cau-
ses malaria invades red blood cells

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Obligate parasites

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normally are free-living, such as
some soil fungi, but they can obtain
nutrients from a host, as many fungi do when they cause skin infections

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Facultative parasites

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Parasites are also categorized according to the duration of their association with their hosts: such as tapeworms, remain in or on a host once they have invaded it.

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Permanent parasites

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Parasites are also categorized according to the duration of their association with their hosts: such as many biting insects, feed on and then leave their hosts.

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Temporary parasites

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Parasites are also categorized according to the duration of their association with their hosts: invade an organism other than their normal host. Ticks that ordinarily attach to dogs or to wild ani- mals sometimes attach to humans; the ticks are then acci- dental parasites.

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Accidental parasites

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Parasites are also categorized according to the duration of their association with their hosts: refers to a parasite itself having parasites. Some mosquitoes, which are temporary parasites, harbor the malaria parasite or other parasites

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Hyperparasitism

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insects serve as ? , or agents of transmission, of many human parasitic diseases.

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vectors

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A vector in which the parasite goes through part of its life cycle is a

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biological vector

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malaria mos-quito is both a ?

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host and a biological vector.

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? is a vector in which the parasite does not go through any part of its life cycle during transit. Flies that carry parasite eggs, bacteria, or viruses from feces to human food are?

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Mechanical vector

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Hosts are classified as ? hosts if they harbor a parasite

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definitive

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reproduces sexually; they are said to be ? if they harbor the parasite during some other developmental stages.

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Intermediate host

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? are infected organisms that make parasites available for transmission to other hosts. ? for human parasitic diseases typically are wild or domestic animal

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Reservoir hosts

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refers to the range of different hosts in which a parasite can mature. Someparasites are quitehost specific—they maturein only one host. T

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Host specificity

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host defense mechanisms: the formation of an outer covering that protects against unfavorable environmental conditions.

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Encystment

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faster than the host can make new antibodies

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parasite’s surface antigens

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cannot react with the parasite’s antigens.

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host’s immune system to make antibodies

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parasites are out of reach of host defense mechanisms.

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Invading host cells

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dog heartworm ? , perforates the heart wall and leaves holes in the heart when the worms die and decay.

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Dirofilaria immitis

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parasites that leave the human body through feces die from

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desiccation

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Some parasites, such as certain protozoa, undergo ? or multiple fission, in which one cell gives rise to many cells, all of which are infective.

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schizogony

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one organism has both male and female reproductive systems andbothare functiona

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Hermaphroditic

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Have chloroplasts; live in moist, sunny environments Examples ex: Euglenoids, diatoms, and dinoflagellates

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Plantlike protists

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Most are saprophytes; may be unicellular or multicellular Ex: Water molds; plasmodial and cellular slime molds

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Funguslike protists

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Heterotrophs; most are unicellular, most are free-living, but some are commensals or parasites Ex: Mastigophorans, sarcodines, apicomplexans, and ciliates

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Animal-like protists

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usually have a single flagellum and pigmented eyespot

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Euglenoids

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pigmented eyespot

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Stigma

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Euglena gracilis ,has an elongated, cigar-shaped, flexible body. Instead of a cell wall, it has a ? , or outer membranous cover.

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pellicle

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? , which lack flagella, is and several other groups, which have flagella and are distinguished by their yellow and brown pigments. ? are an especially numerous group and are important as producers in both freshwater and marine environments.

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diatoms (di0ah-tomz)

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are plantlike protists that usually have two flagella—one extending behind the organism like a tail, and the other lying in a transverse groove

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dinoflagellates (di0no-flaj00el-atz)

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, a tightly affixed, secreted layer that typically contains cellulose.

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theca

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is an uncommon substance in protists, although it is abundant in plants

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Cellulose

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? and related protists that cause mildew—the Oomycota—are sometimes classified as fungi.

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The water molds

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These molds, mildews, and plant blights produce flagellated spores, called ? duringasexual reproduction and large motile gametes during sexual reproduction.

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zoospores

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are commonly found as glistening, viscous masses of slime on rotting logs; they also live in other decaying matter or in soil

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Slime molds

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? form a multinucleate, amoeboid mass called a plasmodium

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Plasmodial slime molds

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, which moves about slowly and phagocytizes dead matter

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plasmodium

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Sometimes a plasmodium stops moving and forms ?

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fruiting bodies.

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produce pseudoplasmodia, fruiting bodies, and spores with characteristics that are quite different

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cellular slime molds

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is a slightly motile aggregation of cells. It produces fruiting bodies, which in turn produce spores. The spores germinate into amoeboid phagocytic cells that divide repeatedly, producing more independent amoeboid cells

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pseudoplasmodium

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are heterotrophic, mostly unicellular organisms, but a few form colonies.

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Protozoa

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which live in or on other organisms without harming them, and a few are parasites

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Commensals

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have flagella. A few species are free-living in either fresh or salt water, but most live in symbiotic relationships with plants or animals.

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mastigophorans (mas00ti-gof0oranz)

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lives in the termite gut and contributes enzymes that digest cellulose.

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Trichonympha

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formerly called sarcodines) move by means of pseudopodia. A few ? have flagella at some stage in their life cycle. They feed mainly on other microorganisms, including other protozoa and small algae.

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amebozoa

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(or sporozoans) are parasitic and immobile. Enzymes present in groups (complexes) of organelles at the tips (apices) of their cells digest their way into host cells, giving the group the name ? These parasites usually have complex life cycles. An important example is the life cycle of the malaria parasite.

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apicomplexans

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which are present as ? in the salivary glands of an infected mosquito, enter human blood through the mosquito’s bite.

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sporozoites

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The sporozoites migrate to the liver and become ?

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merozoites (meh-rozo0itz).

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After about 10 days, they emerge into the blood, invade red blood cells, and become ? . ? reproduce asexually, producing many more merozoites, which are released into the blood by the rupture of red blood cells.

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trophozoites (tro-fo-zo0itz)

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The largest group of protozoans, the ? , have cilia over most of their surfaces. ? have a basal body near their origin that anchors them in the cytoplasm and enables them to extend from the surface of the cell.

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ciliates

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cilia assist in food gathering.

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Paramecium

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only ciliate that parasitizes humans, causes dysentery.

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Balantidium coli,

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? , tentacles that can be used to capture prey, or long stalks by which they attach themselves to surfaces.

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trichocysts

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Ciliates also undergo ?

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Ciliates also undergo conjugation

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studied in the specialized field of mycology, are a diverse group of heterotrophs. Many are saprophytes that digest dead organic matter and organic wastes. Some are parasites that obtain nutrients from the tissues of other organisms

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Fungi

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body of a fungus is called a

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thallus

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The thallus of most multicellular fungi consists of a

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mycelium

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a loosely organized mass of threadlike structures called

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hyphae

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a polysaccharide also found in the exoskeletons (outer coverings) of arthropods such as ticks and spiders.

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Chitin

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many hyphal cells are separated by cross-walls called

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septa (singular: septum

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In one way, haploid gametes unite, and their cytoplasm mingles in a process called

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plasmogamy (

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if the nuclei fail to unite, a ? cell forms; it can persist for several cell divisions

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dikaryotic (‘‘two-nucleus

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Eventually, the nuclei fuse in a process called ? to produce a diploid cell.

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karyogamy (kar00-e-og0am-e)

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are filamentous structures that break through weakened spore walls and develop into hyphae.

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Germ tubes

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In the soil, the production of such toxins, which are antibiotics, is called? .

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antibiosis

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? Often are caused by more than one organism. ? can be classified as superficial, subcutaneous, or systemic.

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Human fungal diseases, or mycoses,

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Affectt only keratinized tissue in the skin, hair, and nails.

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Superficial diseases

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affect skin layers beneath keratinized tissue and can spread to lymph vessels.

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Subcutaneous species

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affect skin layers beneath keratinized tissue and can spread to lymph vessels.

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Subcutaneous disease

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affect skin layers beneath keratinized tissue and can spread to lymph vessels.

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Subcutaneous disease

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invade internal organs and cause significant destruction.

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Systemic disease

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Acidic, high-sugar media with antibiotics added help prevent bacterial growth and allow fungal growth. The medium ? , which was developed nearly a century ago by a French mycologist, is still used in many laboratories

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Sabouraud agar

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Phylum: Zygomycota Common name? Characteristics: Display conjugation Examples: Rhizopus and other bread molds

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Bread molds

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Phylum: Ascomycota Common name? Characteristics: Produce asci and ascospores during sexual reproduction Examples: Neurospora, Penicillium, Saccharomyces, and other yeasts; Candida, Trichophyton, and several other human pathogens

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Sac fungi

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Phylum: Basidiomycota Common name? Characteristics: Produce basidia and basidiospores Examples: Amanita and other mushrooms; Claviceps (which produces ergot); Cryptococcus

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Club fungi

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Phylum: Deuteromycota Common name? Characteristics: Sexual stage nonexistent or unknown Examples: Soil organisms; various human pathogens

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Fungi Imperfecti