D Ciliata. Solution: The presence of two types of nuclei, a macronucleus and a micronucleus, is characteristic of protozoans which are grouped under the Class Ciliata, the Subphylum Ciliophora. They move by cilia throughout life. A localised inflammatory response appears at the site of infection causes redness, swelling, pain and heat due to certain chemicals. They are Human Health and Disease. Phenetic classification of organisms is based on Biological Classification.
Many blue-green algae occur in thermal springs hot water springs. The temperature tolerance of these algae has been attributed to Biological Classification.
Peptidoglycan is a characteristic constituent of the cell wall of Biological Classification. Which of the given statements is wrong? Euglena species also possess chlorophyll within chloroplasts. This pigment allows the organisms to synthesize organic compounds in the presence of sunlight. When no sunlight is available, the organism feeds on dead organic matter in the surrounding environment.
Thus, the organism is autotrophic and heterotrophic. Some biologists consider Euglena to be the basic stock of evolution for both animals and plants. Certain species of Mastigophora are zooflagellates, while some are phytoflagellates. The zooflagellates live within the bodies of animals and are typified by the wood-digesting flagellates in the intestines of termites.
Among the pathogenic zooflagellates are those that cause sleeping sickness, trichomoniasis, and giardiasis. The phytoflagellates have photosynthetic abilities and are often discussed with algae in textbooks. Some species of Mastigophora organize themselves into colonies. Members of the genus Volvox are typical colonial forms. The cell colonies are not differentiated into tissues or organs, but the colonies show how a preliminary step in evolutionary development might have occurred.
Members of the phylum Sarcodina are the amoebas and their relatives. Amoebas consist of a single cell without a definite shape. They feed on small organisms and particles of organic matter, and they engulf the particles by phagocytosis. Extensions of the cytoplasm called pseudopodia the singular is pseudopodium assist phagocytosis and motion in the organisms.
Amoebas are found in most lakes, ponds, and other bodies of freshwater. They move by a creeping form of locomotion called amoeboid motion. One amoeba called Entamoeba histolytica causes a type of dysentery in humans. Two interesting amoebas are the foraminiferans and the radiolarians. Both are marine amoebas that secrete shells. Their shells have been identified as markers for oil deposits because both were present in the ocean communities that became the organic deposits that, under pressure, became oil fields.
Volvox colonies contain to 60, cells, each with two flagella, contained within a hollow, spherical matrix composed of a gelatinous glycoprotein secretion. Individual cells in a Volvox colony move in a coordinated fashion and are interconnected by cytoplasmic bridges. Only a few of the cells reproduce to create daughter colonies, an example of basic cell specialization in this organism. Daughter colonies are produced with their flagella on the inside and have to evert as they are released.
True multicellular organisms, such as the sea lettuce, Ulva , are also represented among the chlorophytes. In addition, some chlorophytes exist as large, multinucleate, single cells. Species in the genus Caulerpa exhibit flattened fern-like foliage and can reach lengths of 3 meters Figure. Caulerpa species undergo nuclear division, but their cells do not complete cytokinesis, remaining instead as massive and elaborate single cells.
Link to Learning Take a look at this video to see cytoplasmic streaming in a green alga. Like the Archaeplastida, the Amoebozoa include species with single cells, species with large multinucleated cells, and species that have multicellular phases. Amoebozoan cells characteristically exhibit pseudopodia that extend like tubes or flat lobes. These pseudopods project outward from anywhere on the cell surface and can anchor to a substrate.
The protist then transports its cytoplasm into the pseudopod, thereby moving the entire cell. This type of motion is similar to the cytoplasmic streaming used to move organelles in the Archaeplastida, and is also used by other protists as a means of locomotion or as a method to distribute nutrients and oxygen.
The Amoebozoa include both free-living and parasitic species. The Gymnamoeba or lobose amoebae include both naked amoebae like the familiar Amoeba proteus and shelled amoebae, whose bodies protrude like snails from their protective tests. Although Pelomyxa may have hundreds of nuclei, it has lost its mitochondria, but replaced them with bacterial endosymbionts.
The secondary loss or modification of mitochondria is a feature also seen in other protist groups. Slime Molds A subset of the amoebozoans, the slime molds, has several morphological similarities to fungi that are thought to be the result of convergent evolution. For instance, during times of stress, some slime molds develop into spore-generating fruiting bodies, much like fungi.
The slime molds are categorized on the basis of their life cycles into plasmodial or cellular types. Plasmodial slime molds are composed of large, multinucleate cells and move along surfaces like an amorphous blob of slime during their feeding stage Figure. Food particles are lifted and engulfed into the slime mold as it glides along. Upon maturation, the plasmodium takes on a net-like appearance with the ability to form fruiting bodies, or sporangia, during times of stress.
Haploid spores are produced by meiosis within the sporangia, and spores can be disseminated through the air or water to potentially land in more favorable environments. If this occurs, the spores germinate to form ameboid or flagellate haploid cells that can combine with each other and produce a diploid zygotic slime mold to complete the life cycle.
The cellular slime molds function as independent amoeboid cells when nutrients are abundant. When food is depleted, cellular slime molds aggregate into a mass of cells that behaves as a single unit, called a slug. Some cells in the slug contribute to a 2—3-millimeter stalk, drying up and dying in the process. Cells atop the stalk form an asexual fruiting body that contains haploid spores Figure.
As with plasmodial slime molds, the spores are disseminated and can germinate if they land in a moist environment. One representative genus of the cellular slime molds is Dictyostelium , which commonly exists in the damp soil of forests. View this video to see the formation of a fruiting body by a cellular slime mold. The Opisthokonts are named for the single posterior flagellum seen in flagellated cells of the group.
The flagella of other protists are anterior and their movement pulls the cells along, while the opisthokonts are pushed.
Protist members of the opisthokonts include the animal-like choanoflagellates, which are believed to resemble the common ancestor of sponges and perhaps, all animals. Choanoflagellates include unicellular and colonial forms Figure , and number about described species.
In these organisms, the single, apical flagellum is surrounded by a contractile collar composed of microvilli. The collar is used to filter and collect bacteria for ingestion by the protist. A similar feeding mechanism is seen in the collar cells of sponges, which suggests a possible connection between choanoflagellates and animals. The Mesomycetozoa form a small group of parasites, primarily of fish, and at least one form that can parasitize humans. Their life cycles are poorly understood.
These organisms are of special interest, because they appear to be so closely related to animals. In the past, they were grouped with fungi and other protists based on their morphology. The next three supergroups all contain at least some photosynthetic members whose chloroplasts were derived by secondary endosymbiosis.
They also show some interesting variations in nuclear structure, and modification of mitochondria or chloroplasts. The Rhizaria supergroup includes many of the amoebas with thin threadlike, needle-like or root-like pseudopodia Figure , rather than the broader lobed pseudopodia of the Amoebozoa.
Many rhizarians make elaborate and beautiful tests—armor-like coverings for the body of the cell—composed of calcium carbonate, silicon, or strontium salts. Rhizarians have important roles in both carbon and nitrogen cycles. When rhizarians die, and their tests sink into deep water, the carbonates are out of reach of most decomposers, locking carbon dioxide away from the atmosphere.
The biological carbon pump is a crucial component of the carbon cycle that maintains lower atmospheric carbon dioxide levels. Foraminiferans are unusual in that they are the only eukaryotes known to participate in the nitrogen cycle by denitrification, an activity usually served only by prokaryotes. Foraminiferans Foraminiferans, or forams, are unicellular heterotrophic protists, ranging from approximately 20 micrometers to several centimeters in length, and occasionally resembling tiny snails Figure.
As a group, the forams exhibit porous shells, called tests that are built from various organic materials and typically hardened with calcium carbonate. The tests may house photosynthetic algae, which the forams can harvest for nutrition. Foram pseudopodia extend through the pores and allow the forams to move, feed, and gather additional building materials.
Typically, forams are associated with sand or other particles in marine or freshwater habitats. Foraminiferans are also useful as indicators of pollution and changes in global weather patterns. Radiolarians A second subtype of Rhizaria, the radiolarians, exhibit intricate exteriors of glassy silica with radial or bilateral symmetry Figure. Needle-like pseudopods supported by microtubules radiate outward from the cell bodies of these protists and function to catch food particles.
The shells of dead radiolarians sink to the ocean floor, where they may accumulate in meter-thick depths. Preserved, sedimented radiolarians are very common in the fossil record. Cercozoa The Cercozoa are both morphologically and metabolically diverse, and include both naked and shelled forms.
The Chlorarachniophytes Figure are photosynthetic, having acquired chloroplasts by secondary endosymbiosis. The chloroplast contains a remnant of the chlorophyte endosymbiont nucleus, sandwiched between the two sets of chloroplast membranes.
Chromalveolata Current evidence suggests that species classified as chromalveolates are derived from a common ancestor that engulfed a photosynthetic red algal cell, which itself had already evolved chloroplasts from an endosymbiotic relationship with a photosynthetic prokaryote. Therefore, the ancestor of chromalveolates is believed to have resulted from a secondary endosymbiotic event.
However, some chromalveolates appear to have lost red alga-derived plastid organelles or lack plastid genes altogether. Therefore, this supergroup should be considered a hypothesis-based working group that is subject to change. Chromalveolates include very important photosynthetic organisms, such as diatoms, brown algae, and significant disease agents in animals and plants.
The chromalveolates can be subdivided into alveolates and stramenopiles. A large body of data supports that the alveolates are derived from a shared common ancestor. The alveolates are named for the presence of an alveolus, or membrane-enclosed sac, beneath the cell membrane. The exact function of the alveolus is unknown, but it may be involved in osmoregulation. The alveolates are further categorized into some of the better-known protists: the dinoflagellates, the apicomplexans, and the ciliates.
Dinoflagellates exhibit extensive morphological diversity and can be photosynthetic, heterotrophic, or mixotrophic. The chloroplast of photosynthetic dinoflagellates was derived by secondary endosymbiosis of a red alga.
Many dinoflagellates are encased in interlocking plates of cellulose. Two perpendicular flagella fit into the grooves between the cellulose plates, with one flagellum extending longitudinally and a second encircling the dinoflagellate Figure.
Together, the flagella contribute to the characteristic spinning motion of dinoflagellates. These protists exist in freshwater and marine habitats, and are a component of plankton , the typically microscopic organisms that drift through the water and serve as a crucial food source for larger aquatic organisms. Dinoflagellates have a nuclear variant called a dinokaryon. The chromosomes in the dinokaryon are highly condensed throughout the cell cycle and do not have typical histones.
Mitosis in dinoflagellates is closed, that is, the spindle separates the chromosomes from outside of the nucleus without breakdown of the nuclear envelope. Some dinoflagellates generate light, called bioluminescence , when they are jarred or stressed. Large numbers of marine dinoflagellates billions or trillions of cells per wave can emit light and cause an entire breaking wave to twinkle or take on a brilliant blue color Figure. For approximately 20 species of marine dinoflagellates, population explosions also called blooms during the summer months can tint the ocean with a muddy red color.
This phenomenon is called a red tide, and it results from the abundant red pigments present in dinoflagellate plastids. In large quantities, these dinoflagellate species secrete an asphyxiating toxin that can kill fish, birds, and marine mammals. Red tides can be massively detrimental to commercial fisheries, and humans who consume these protists may become poisoned. The apicomplexan protists are named for a structure called an apical complex Figure , which appears to be a highly modified secondary chloroplast.
The apicoplast genome is similar to those of dinoflagellate chloroplasts. The apical complex is specialized for entry and infection of host cells. Indeed, all apicomplexans are parasitic. This group includes the genus Plasmodium , which causes malaria in humans.
Apicomplexan life cycles are complex, involving multiple hosts and stages of sexual and asexual reproduction. The ciliates, which include Paramecium and Tetrahymena , are a group of protists 10 to 3, micrometers in length that are covered in rows, tufts, or spirals of tiny cilia.
By beating their cilia synchronously or in waves, ciliates can coordinate directed movements and ingest food particles. Certain ciliates have fused cilia-based structures that function like paddles, funnels, or fins. Ciliates also are surrounded by a pellicle, providing protection without compromising agility.
The genus Paramecium includes protists that have organized their cilia into a plate-like primitive mouth, called an oral groove, which is used to capture and digest bacteria Figure. Food captured in the oral groove enters a food vacuole, where it combines with digestive enzymes. Waste particles are expelled by an exocytic vesicle that fuses at a specific region on the cell membrane, called the anal pore.
In addition to a vacuole-based digestive system, Paramecium also uses contractile vacuoles , which are osmoregulatory vesicles that fill with water as it enters the cell by osmosis and then contract to squeeze water from the cell. Ciliates therefore exhibit considerable structural complexity without having achieved multicellularity. Link to Learning Watch the video of the contractile vacuole of Paramecium expelling water to keep the cell osmotically balanced.
Paramecium has two nuclei, a macronucleus and a micronucleus, in each cell. The micronucleus is essential for sexual reproduction, and is in many ways a typical eukaryotic nucleus, except that its genes are not transcribed. The transcribed nucleus is the macronucleus, which directs asexual binary fission and all other biological functions. The macronucleus is a multiploid nucleus constructed from the micronucleus during sexual reproduction. Periodic reconstruction of the macronucleus is necessary because the macronucleus divides amitotically, and thus becomes genetically unbalanced over a period of successive cell replications.
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