Current Events and History

Phyla

Taxonomists do not always agree on the usage of even the most common terms. Some textbooks and other publications will use alternate names or spellings to describe taxonomic groups, or will lump or split groups in different ways.

Under NAQT rules, unless the question states otherwise, both Latin names (Mollusca) or Anglicized names (molluscs) are acceptable for a given taxon.

Note that spelling and pronunciation are not completely standardized in the taxonomic world, so other sources may have slightly different versions of these phyla.

1. 
   Porifera (pore-IH-fer-ah; 5,000 species) The sponges are all water-dwellers (98% marine, 2% freshwater), and are sometimes classified separately from other animals because of their asymmetric bodies and lack of distinct tissues. They are sessile (immobile) except in early dispersing stages, and collect food particles via the sweeping motions of flagellated cells called choanocytes [koh-ANN-oh-sites].
   
2. 
   Cnidaria (nih-DARE-ee-ya; 10,000 species) Also called Coelenterata [se-LEN-ter-AH-tah], the cnidarians develop from a diploblastic (two-layered) embryo, and have two separate tissue layers and radial body symmetry. Many cnidarians have two life stages, the mobile, usually bell-like medusa and the sessile polyp. All cnidarians have nematocysts, or stinging cells, for capturing prey, and some can inflict painful stings on swimmers. Examples include the hydras, sea anemones, corals, jellyfishes, and Portuguese man-o-war (which is actually an aggregation of colonial cnidarians).
   
3. 
   Platyhelminthes (PLAT-ee-hel-MIN-theez; 15,000 species) The flatworms are the most primitive phylum to develop from a triploblastic (three-layered) embryo. They have bilateral body symmetry, and are acoelomate (lacking a true body cavity), so that the space between the digestive tract and the body wall is filled with tissue. As the name implies, they are generally flat-bodied. They have a true head and brain, but the digestive system has only one opening that functions as both mouth and anus. Most are hermaphroditic. This phylum includes parasites such as the tapeworms and flukes, as well as free-living (i.e., non-parasitic) organisms such as the planarians.
   
4. 
   Nematoda (NEM-ah-TOE-dah; 15,000 species) The roundworms are unsegmented worms that live in a variety of habitats. They are pseudocoelomate; the three tissue layers are concentric, but the body cavity is not lined with tissue derived from the mesoderm (middle embryonic layer). They include both free-living and parasitic species; human parasites include hookworms and the causative agents of elephantiasis, trichinosis, and river blindness. Soil nematodes may be crop pests, while others are beneficial predators on other plant pests. The nematode species Caenorhabdis elegans is a common subject in genetics and developmental-biology labs.
   
5. 
   Annelida (AN-el-LEE-dah; 11,500 species) The annelids are segmented worms and represent the first lineage of truly eucoelomate (having a body cavity lined with mesoderm-derived tissue) animals; their body cavities are lined with tissue derived from the embryonic mesoderm. Annelid classes include the marine Polychaeta, as well as the mostly terrestrial Oligochaeta (including the earthworms, Lumbricus) and the mostly-aquatic Hirudinea, or leeches. Characteristics of annelids include nephridia (kidney-like structures), blood vessels, and, in some classes, hermaphroditism.
   
6. 
   Arthropoda (ar-THROP-oh-dah or AR-thro-POE-dah; over 800,000 species described; estimates of actual diversity vary but go as high as 9 million species) The most diverse and successful animal phylum on earth (incorporating about 75% of all described animal species), the Arthropoda are characterized by jointed legs and a chitinous exoskeleton. Like annelids, they are segmented, but unlike annelids, their segments are usually fused into larger body parts with specialized functions (such as the head, thorax, and abdomen of an insect). Arthropods are often divided into four subphyla: Uniramia (insects, centipedes, millipedes); Chelicerata (arachnids, sea spiders, horseshoe crabs); Crustacea (shrimps, lobsters, crabs, crayfish, barnacles, pillbugs), and Trilobitomorpha (the trilobites, now extinct).
   
7. 
   Cycliophora (CY-clee-oh-FORE-ah; 1 species) The most recently named phylum; its only known member is Symbion pandora, a tiny invertebrate first identified in 1995 when a Danish biologist found specimens on the mouthparts of a Norwegian lobster. It is believed to be closely related to the marine phyla Entoprocta and Ectoprocta (Bryozoa), which are not discussed here.
   
8. 
   Mollusca (mol-LUS-kah; 50,000 species) The molluscs are second in diversity only to the arthropods. Body plans within this phylum are diverse, but general characteristics include a soft body covered by a thin mantle, with a muscular foot and an internal visceral mass. There are two fluid-filled body cavities derived from mesodermal tissue; a small coelom and a large hemocoel that functions as an open circulatory system. Many molluscs have a shell composed of calcium carbonate and proteins, secreted by the mantle. Familiar groups within the Mollusca include the classes Gastropoda (slugs, snails), Bivalvia (clams, oysters, scallops), and Cephalopoda (nautilus, squids, octopi).
   
9. 
   Echinodermata (ek-KY-no-der-MAH-tah; 6,500 species) Characteristics of this phylum include an endoskeleton composed of many ossicles of calcium and magnesium carbonate, a water vascular system (WVS), a ring canal around the esophagus, and locomotion by tube feet connected to the WVS. Unique to echinoderms is the five-fold radial symmetry obvious in sea stars (seafish), sea urchins, and sea lilies. Others, like sea cucumbers, have varying degrees of bilateral symmetry. In the echinoderm body plan, a true head is absent; the anatomical terms oral (mouth-bearing) and aboral (away from the mouth) are used to describe orientation of the body surfaces. Feeding adaptations include particle feeding through the WVS, everting the stomach to engulf prey (sea stars), and a scraping device called Aristotle's lantern (sea urchins).
   
10. 
    Chordata (kor-DAH-tah; 44,000 species) Our home phylum is divided into three subphyla: Urochordata, the sea squirts; Cephalochordata, the lancelets, and the true vertebrates (Vertebrata, the most diverse subphylum). Defining traits of chordates include pharyngeal gill slits, a notochord, a post-anal tail, and a dorsal hollow nerve cord. In vertebrates, some of these structures are found only in embryonic stages. The lancelet Amphioxus (Branchiostoma) is often used as a demonstration organism in biology labs.
    

1. 
   Charon (Pluto) Named for the mythical boatman of the Greek underworld. Its expected pronunciation of "KAIR-en" is not the correct one, which is actually "SHAHR-en", in honor of Charlene Christy, wife of Jim Christy, its discoverer. The largest moon relative to the size of its orbiting planet, Charon not only is in synchronous orbit with Pluto, but the two show the same face toward each other at all times. The relative sizes of the two bodies has led some to call Charon and Pluto a double planet system. Charon's surface is believed to be water ice.
   
2. 
   Deimos and Phobos (Mars) Named for two sons of Ares and Aphrodite. Phobos and Deimos (Greek for "fear" and "panic") are the two moons of Mars and both were discovered in 1877 by Asaph Hall. Phobos orbits closer to the planet and has as its most prominent feature the crater Stickney (Hall's wife's maiden name). Unlike the Earth's moon, it rises in the west and sets in the east, about twice per Martian day. This is due to it being below the radius for synchronous orbit. This position also means it will either impact Mars or break into a ring in around 50 million years. Deimos is the smallest moon in the solar system. It was discovered two days before Phobos. Deimos was likely an asteroid brought into Mars' orbit after being disturbed by Jupiter.  Like Phobos, Deimos is heavily cratered, rich in carbon, and believed to have water ice.
   
3. 
   Europa (Jupiter) One of the Galilean moons, discovered in 1610 by Galileo (the others are Callisto, Ganymede, and Io). It resembles Io, and to a degree, Earth, in its composition of silicate rocks. However, it is coated in a thin layer of ice, which causes it to be exceedingly smooth. This ice layer may also provide a thin atmosphere as hydrogen and oxygen are released when the planet is exposed to sunlight. There is the possibility of an active sea of liquid water beneath the surface. The most striking feature of the surface is a series of dark streaks that may be due to geysers or volcanic eruptions.
   
4. 
   Ganymede (Jupiter) The largest satellite in the solar system, this Galilean moon is larger than Mercury, but has only half its mass. Based on the observations of the Galileo spacecraft, it is thought to have a three-layer structure of a molten iron core, silicate mantle, and ice exterior. Its surface is marked by older, dark, highly cratered regions, mixed with lighter, grooved regions. These grooves indicate tectonic activity, but Ganymede does not appear to have undergone recent tectonic shifts.
   
5. 
   Io (Jupiter) Like Europa, Io (named for a lover of Zeus) is primarily formed of silicate rock. Its surface, however, is unlike any other satellite. Rather than craters, Io is dotted with active volcanoes, calderas, and other signs of geological activity. The eruptions are believed to consist of sulfurous compounds that comprise Io's thin atmosphere. The tremendous activity is due to tidal warming from the gravity of Jupiter and other satellites. Additionally, as Io orbits it is heated electrically from currents produced by Jupiter's magnetic field. This action strips material from Io, producing a radiation field and increasing Jupiter's magnetosphere.
   
6. 
   Nereid (Neptune) Discovered by Gerard Kuiper (who also discovered Miranda, Titan's atmosphere, and an asteroid belt), Nereid (named for the daughters of Nereus and Doris) has the most eccentric orbit of any known satellite, ranging from 1.3 million kilometers to 9.6 million. The oddity of this orbit indicates it is likely a captured asteroid.
   
7. 
   Oberon (Uranus) Named for the King of the Fairies in A Midsummer Night's Dream (all of Uranus' satellites are named for literary, rather than mythological, characters), Oberon is both the second largest of Uranus' satellites, and the outermost of its large satellites. Like all large Uranian moons, its structure is about half water ice, half rock. Large faults are visible across its southern hemisphere, but its surface is heavily cratered, indicating long-term tectonic stability. Some craters have dark floors that could possibly indicate post-impact upwellings of water.
   
8. 
   Titan (Saturn) The largest of Saturn's satellites, Titan might be the largest satellite in the solar system, but this awaits more accurate measurements. Those measurements are difficult because of Titan's major characteristic: It is the only satellite to have a substantial atmosphere. Its significant atmosphere, a mix of nitrogen (80%), methane (20%), and argon (trace), also makes it unique among satellites.
   
9. 
   Titania (Uranus) Another of Herschel's discoveries, Titania is named for Oberon's wife, the Queen of the Fairies, and is the largest of the Uranian satellites. Its surface is an odd mix of craters and valleys. One theory regarding this is that it began as a liquid, then cooled surface first. Once ice had formed, the interior, freezing forced surface cracks which formed the valleys. This also accounts for the appearance of some craters, where ice appears to have melted and filled in.
   
10. 
    Triton (Neptune) By far the largest of Neptune's satellites, Triton is also unusual for its retrograde orbit, which indicates that it was not part of the natural formation of Neptune's other moons. It also features seismic activity in the form of ice volcanoes, a tenuous nitrogen-methane atmosphere, and a southern hemisphere "ice cap" of nitrogen and methane. All of these may be caused by Triton's odd rotational axis, which tends to alternate polar and equatorial regions facing the sun.
    

The word "organelle" comes from the Latin for "little organ," which fits their function as organized structures found within cells that allow the cell to survive.

1. 
   Nucleus The nucleus is the "command central" of the cell because it contains almost all of the cell's DNA, which encodes the information needed to make all the proteins that the cell uses. The DNA appears as chromatin through most of the cell cycle but condenses to form chromosomes when the cell is undergoing mitosis. Commonly seen within the nucleus are dense bodies called nucleoli, which contain ribosomal RNA. In eukaryotes, the nucleus is surrounded by a selectively-permeable nuclear envelope.
   
2. 
   Ribosomes Ribosomes are the machines that coordinate protein synthesis, or translation. They consist of several RNA and protein molecules arranged into two subunits. Ribosomes read the messenger RNA copy of the DNA and assemble the appropriate amino acids into protein chains.
   
3. 
   Mitochondria The "mighty mitos" are the powerhouses of the cell. Mitochondria are double-membrane-bound organelles that are the site of respiration and oxidative phosphorylation, processes that produce energy for the cell in the form of ATP. The inner membrane of a mitochondrion forms folds called cristae [KRIS-tee], which are suspended in a fluid called the matrix. The mitochondrial matrix contains DNA and ribosomes.
   
4. 
   Endoplasmic Reticulum (ER) The ER is a network of tube-like membranes continuous with the nuclear envelope that comes in rough (with ribosomes) and smooth (without ribosomes) varieties. In the ER, proteins undergo modifications and folding to yield the final, functional protein structures.
   
5. 
   Golgi Apparatus The stack of flattened, folded membranes that forms the Golgi apparatus acts as the "post office of the cell." Here proteins from the ribosomes are stored, chemically modified, "addressed" with carbohydrate tags, and packaged in vesicles for delivery.
   
6. 
   Lysosomes Lysosomes are membrane-bound organelles that contain digestive enzymes that break down proteins, lipids, carbohydrates, and nucleic acids. They are important in processing the contents of vesicles taken in from outside the cell. It is crucial to maintain the integrity of the lysosomal membranes because the enzymes they contain can digest cellular components as well.
   
7. 
   Chloroplasts Found only in plants and certain protists, the chloroplast contains the green pigment chlorophyll and is the site of photosynthesis. Like the mitochondrion, a chloroplast is a double-membrane-bound organelle, and it has its own DNA and ribosomes in the stroma. Chloroplasts contain grana, which are stacks of single membrane structures called thylakoids on which the reactions of photosynthesis occur.
   
8. 
   Vacuoles Found mainly in plants and protists, vacuoles are liquid-filled cavities enclosed by a single membrane. They serve as storage bins for food and waste products. Contractile vacuoles are important for freshwater protists to rid their cells of excess water that accumulates because of salt imbalance with the environment.
   
9. 
   Cilia/Flagella Cilia and flagella are important organelles of motility, which allow the cell to move. Flagella are long, whip-like structures, while cilia are short hair-like projections. Both contain a 9 + 2 arrangement of microtubules in cross section and are powered by molecular motors of kinesin and dynein molecules.
   
10. 
    Centrioles Not found in plant cells, centrioles are paired organelles with nine sets of microtubule triplets in cross section. They are important in organizing the microtubule spindle needed to move the chromosomes during mitosis.
    

1. 
   Gabriel García Marquez (1928-present, Colombia; Nobel Prize for Literature 1982). The master of magic realism, his birthplace of Aracataca was the model for the fictional town of Macondo. The town played a prominent role in many of García Marquez's works, such as Leaf Storm and his seminal novel, One Hundred Years of Solitude (1967), which details the decline of the Buendía family over seven generations. A newspaper journalist in the 1950s, García Marquez exposed a naval scandal (chronicled in The Story of a Shipwrecked Sailor). Other prominent novels include In Evil Hour, Love in the Time of Cholera, and The General in His Labyrinth, a depiction of Simón Bolívar's final years.
   
2. 
   Pablo Neruda (1904-1973, Chile; Nobel 1971). Born Neftalí Reyes, he adopted the surname of the 19th century Czech poet Jan Neruda. Gabriela Mistral (see below) was the head of his school in the small city of Temuco. 1923 saw the publication of Neruda's best-known work, Twenty Love Poems and a Song of Despair, which led to diplomatic appointments. As a penniless consul in Burma in the 1930s, he wrote the surrealist collection Residence on Earth. He served in the Chilean senate in the 1940s, though government opponents forced him into exile over his Communist views. Crossing the Andes on horseback inspired his epic Canto general (1950). He died of cancer days after his friend Salvador Allende was executed.
   
3. 
   Jorge Luis Borges (1899-1986, Argentina). One-quarter English, Borges learned that language before he learned Spanish. Educated in Europe during World War I, he met a circle of avant-garde poets in Spain, which inspired him to found the ultraismo movement and publish the collection Fervor of Buenos Aires (1923) when he returned to Argentina. While working in a library, Borges developed his greatest short stories, collected in A Universal History of Infamy (1935), Ficciones (1944), and The Aleph (1949). By his fifties, a disorder inherited from his father had taken Borges's eyesight, but in 1962 he completed the influential story collection Labyrinths.
   
4. 
   Isabel Allende (1942-present, Chile). Actually born in Peru, at age three she moved to her mother's native Chile. A successful news reporter in her twenties, she and her family fled to Venezuela after General Augusto Pinochet deposed and executed her uncle Salvador Allende, setting up a dictatorship. Her formal literary career began at age 40, when she published The House of the Spirits, a magic realist work that chronicles several generations of the Trueba family. Other works of fiction include the short-story collection Eva Luna (1989) and Paula (1995), which detailed Allende's care for her terminally ill daughter.
   
5. 
   Gabriela Mistral (1889-1957, Chile; Nobel 1945). The first Latin American to win the Nobel Literature Prize, Mistral was actually named Lucila Godoy Alcayaga, but took her pen name from the Italian and French poets Gabriele D'Annunzio and Frédéric Mistral respectively. At first a prominent educator, she wrote "Sonnets of Death" (1914) after the suicide of her fiancé. Those sonnets later appeared in her most famous collection, Desolation (1922). A native Chilean, she served as a diplomat both in the United States and Europe. Langston Hughes translated a portion of Mistral's poetry into English just after she died.
   
6. 
   Octavio Paz (1914-1998, Mexico; Nobel 1990). A prominent poet and essayist, Paz supported leftist causes in Mexico; he fought briefly for the Republicans during the Spanish Civil War. He published the poetry collection Luna silvestre at age 19, and his 584-line poem The Sun Stone deals with the planet Venus, an important symbol to the Aztecs. While studying in Los Angeles, Paz observed flamboyantly dressed Mexican-American pachucos ("zoot-suiters"), who inspired him to write about Mexico and its Native American/mestizo heritage in his pivotal essay collection, The Labyrinth of Solitude (1950). Another prose work, In the Light of India (1997), reflected Paz's part-(East) Indian heritage.
   
7. 
   José Martí (1853-1895, Cuba). Best known as a poet and a revolutionary, Martí fought tirelessly for Cuban independence. Imprisoned at age sixteen and exiled from the island several times, he settled in New York for the last fifteen years of his life, where he wrote essays on Walt Whitman, Jesse James, and the threat of Latin American economic dependence on the United States. His Ill-Omened Friendship (1885) is considered the first Spanish modernist novel, and his poetry collections include Our America and Simple Verses; the poem "Guantanamera" was the inspiration for several songs. Martí was killed in a skirmish at Dos Ríos while participating in an invasion with other Cuban exiles.
   
8. 
   Mario Vargas Llosa (1936-present, Peru). While attending military school in Lima, Vargas Llosa wrote the play The Escape of the Inca (1952), but the harsh treatment he received there was the basis for his best-known novel, The Time of the Hero. Conversation in the Cathedral (1969) was Vargas Llosa's serious take on living under the dictatorship of Manuel Odría, while in 1977 he published the lighter, autobiographical Aunt Julia and the Scriptwriter, about soap operas. Other important works include The War of the End of the World and A Fish in the Water, which discusses his political career; Vargas Llosa ran for president of Peru in 1990 but was defeated by Alberto Fujimori.
   
9. 
   Miguel Asturias (1899-1974, Guatemala; Nobel 1967). Asturias left his native Guatemala in 1923 to study in Paris. There he discovered Mayan mythology, and translated the Popol Vuh into Spanish; the theme would pervade his work, such as 1963's Mulata de tal. He most famous novel, El señor presidente (1946), was a satire against the oppressive Guatalemalan dictatorship. Asturias also completed a trilogy that blasted exploitation by the American-led United Fruit Company, and the short-story collection Weekend in Guatemala (1956), based on the CIA-led overthrow of president Jacobo Arbenz's liberal government.
   
10. 
    Carlos Fuentes (1928-present, Mexico). Though born into a well-to-do family, Fuentes has often dealt with the betrayed ideals from the Mexican Revolution of 1910, the subject of both his first novel, Where the Air is Clear (1958), and his most successful book, The Death of Artemio Cruz (1962). Other notable novels include Terra nostra, set during the reign of King Philip II of Spain, and The Old Gringo, which portrays Ambrose Bierce's last days in Mexico. Fuentes has also penned absurdist plays and essay collections on Mexican and American art and literature.