Chapter 5- The eukaryotes of microbiology Flashcards
Protist
Refers to a diverse group of microscopic eukaryotic organisms. It is not considered a formal taxonomic term because the organisms it describes do not have a shared evolutionary origin. Historically, the protists were informally grouped into the “animal-like” protozoans, the “plant-like” algae, and the “fungus-like” protists such as water molds.
Plankton
An informal term used to describe microorganisms that drift or float in water.
Trophozoites
Describes protozoans during the feeding and growth part of their life cycle. They feed on small particles of food, like bacteria. Some protozoa stay in this stage, others develop into a cyst stage
Encystment
The process by which a trophozoite becomes a cyst. This occurs when environmental conditions are too harsh for a trophozoite. Eimeria is a protozoan genus that is capable of encystment
Excystment
When cysts are triggered by environmental cues to become active again.
Cyst
A cell with a protective wall.
Schizogony
The nucleus of a cell divides multiple times before the cell divides into many smaller cells. This is an asexual method of reproduction for protozoans
3 types of asexual reproduction in protozoa
Binary fission, budding, or schizogony
Merozoites
Products of schizogony, they are stored in structures called schizonts.
Syngamy
When a protozoa’s haploid gametes fuse
Conjugation
When protozoa’s gametes join to exchange DNA. It is a true form of eukaryotic sexual reproduction between two cells of different mating types. It is found in ciliates, a group of protozoans
Plasmalemma
The plasma membrane of protozoans. Some protists, including protozoans, have distinct layers of cytoplasm under the membrane. In these protists, the outer gel layer (with microfilaments of actin) is called the ectoplasm. Inside this layer is a fluid region of cytoplasm called the endoplasm. The membrane structures contribute to complex shell shapes in some protozoans
Protozoa
Nonphotosynthetic, motile organisms
that are always unicellular. They are heterotrophic. . Mitochondria may be absent in parasites or altered to kinetoplastids (modified mitochondria) or hydrogenosomes
Pellicle
A structure in the plasma membrane of protozoans, formed by bands of proteins. It adds to rigidity in the membrane
Cytostome
A specialized structure of taking in food through phagocytosis in protozoans. Oral grooves leading to cytostomes are lined with hair-like cilia to sweep in food particles
Cytoproct
A specialized structure for the exocytosis of wastes in protozoans
Holozoic
Protozoans that ingest whole food particles through phagocytosis
Saprozoic
Protozoans that ingest small, soluble food molecules
How are protists able to move?
Some have flagella or hairs (cilia) made of microtubules that they can use for movement. Others use extensions of the cytoplasm (pseudopodia) to attach the cell to the surface and cytoplasm moves into the extensions so the cell can move forward
Contractile vacuoles
Organelles that can be used to move water out of the cell for osmotic regulation (salt and water balance)
Polyphyletic
Protists are polyphyletic because they lack a shared evolutionary origin. They are all eukaryotic and are therefore all in the domain Eukarya, but protists are scattered across different taxonomic groups
Amoebozoa
A eukaryotic supergroup that includes protozoans that use amoeboid movement. Includes subgroups entamoebas and slime molds
Amoeboid movement
Actin microfilaments produce
pseudopodia. Protoplasm flows into the extensions and moves the organism.
Entamoeba
A genus that is a subgroup of the eukaryotic supergroup Amoebozoa. Includes commensal or parasitic species, including the medically important E. histolytica, which is transmitted by cysts in feces and is the primary cause of amoebic dysentery. Another member of this group
that is pathogenic to humans is Acanthamoeba, which can cause keratitis (corneal inflammation) and blindness
Slime molds
A group of organisms that is a subgroup of the eukaryotic supergroup Amoebozoa. They are classified into cellular slime molds and plasmodial slime molds.
Cellular slime molds
The cellular slime molds exist as individual amoeboid cells that periodically aggregate into a mobile slug. The aggregation of cells forms a “fruiting body”, which can produce haploid spores
Plasmodial slime molds
Large, multinucleate amoeboid cells that form reproductive stalks to produce spores that divide into gametes
Chromalveolata (4)
A eukaryotic supergroup united by similar origins of its members’ plastids. Includes the apicomplexans, ciliates, diatoms, and dinoflagellate
Apicomplexans
A member of the supergroup Chromalveolata. They are parasites that can be intracellular or extracellular. They have an apical complex at one end of the cell, where organelles, vacuoles, and microtubules are concentrated. This concentration of structures allows the parasite to enter host cells. Apicomplexans have complex life cycles that include an
infective sporozoite that undergoes schizogony to make many merozoites, and requires transmission between multiple hosts. The genus Plasmodium is an example of this group. Another example is Toxoplasma gondii, which causes toxoplasmosis and can be transmitted from cat feces, unwashed fruit and vegetables, or from undercooked meat.
Toxoplasmosis can be associated with serious birth defects
Ciliates
Located within the supergroup Chromalveolata. They are a diverse group characterized by cilia on their cell surface. Cilia can be used for locomotion or feeding. These organisms have a micronucleus and a macronucleus. Balantidium coli is the only parasitic ciliate that affects humans by causing intestinal illness, although it rarely causes serious medical issues except in the immunocompromised
Micronucleus
Diploid, somatic, and used for sexual reproduction by conjugation.
Macronucleus
Derived from the micronucleus- the macronucleus becomes polyploid (multiple sets of duplicate chromosomes), and has a reduced set of metabolic genes.
How do ciliates reproduce?
Through conjugation. Two cells attach to each other, and the diploid micronuclei undergo meiosis in each cell. Eventually, one haploid micronucleus and the macronucleus are left in each cell. The haploid micronucleus undergoes mitosis. s. The two cells then exchange one micronucleus each, which fuses with the remaining micronucleus present to form
a new, genetically different, diploid micronucleus. The diploid micronucleus undergoes two mitotic divisions, so each cell has four micronuclei, and two of the four combine to form a new macronucleus. The chromosomes in the macronucleus replicate until it’s polyploid, and the two cells separate. The two cells are now genetically different from each other and from their previous versions.
Oomycetes
Similar to fungi, but have several different characteristics. Located within the supergroup Chromalveolata. They have cell walls of cellulose (unlike the chitinous cell walls of fungi) and they are generally diploid, whereas the dominant life forms of fungi are typically haploid. One example is Phytophthora, the plant pathogen found in the soil that caused the Irish potato famine
Excavata
A eukaryotic supergroup. Includes primitive eukaryotes and parasites with limited metabolic abilities. These organisms often have a depression on the cell surface, called an excavate. Includes the subgroups Fornicata, Parabasalia, and Euglenozoa.
Fornicata
Part of the supergroup Excavata. They have flagella, but no mitochondria. One example is Giardia lamblia, which causes diarrheal illness and can be spread through cysts from feces that contaminate water
supplies
Parabasalia
Part of the supergroup Excavata. Live in animals as part of an endosymbiotic relationship. They live in the intestines of animals like termites and cockroaches. They have basal bodies and modified mitochondria (kinetoplastids). They also have a large, complex cell structure with an undulating membrane and often have many flagella. Includes pathogens such as Trichomonas vaginalis, which causes the human sexually transmitted disease trichomoniasis. In women, it causes vaginal discomfort and can cause complications in pregnancy.
Euglenozoa
Part of the supergroup Excavata. Can be photosynthetic, but others are not. Includes members of the genus Euglena and trypanosomes, which are parasitic pathogens.