Biology O
What is obligate aerobe ?
Any organism that must utilize atmospheric oxygen in its metabolic pathways and for cellular respiration, and cannot survive without it. The adjective obligate refers to an environmental factor.
What is obligate anaerobe ?
Any organism where atmospheric oxygen is toxic to its growth; growth can occur only in an anaerobic environment. The adjective obligate refers to an environmental factor.
What is oceanic zone ?
The ocean is divided into zones. The whole mass of water is called the pelagic. This is divided into two major subzones: the neritic zone, which covers all water to a depth of 600 feet, and the oceanic zone, which covers all water below 600 feet. The oceanic zone is further divided into subzones. The mesopelagic (semidark waters) covers the depths from 650 feet to 3,200 feet, which is the middle layer between the upper (sunlit 650 feet) epipelagic and the lower (cold and dark) bathypelagic.
What is olfaction ?
The process of smell. In humans, chemoreceptors are located in a patch of tissue about the size of a postage stamp, called the olfactory epithelium, that is located high in the nasal cavity.
What is oligochaete ?
Worms of the phylum Annelida, class Oligochaetae. Chiefly terrestrial and freshwater worms with distinct body segmentation and no apparent head. The earthworm is a familiar example.
What is oligogyny ?
Multiple egg-laying queens that each have their own territory within a colony.
What is oligonucleotide ?
Macromolecules composed of short SEQUENCEs of NUCLEOTIDES that are usually synthetically prepared and used, for example, in site-directed MUTAGENESIS.
What is oligotrophic lake ?
A condition of a lake that has low concentrations of nutrients and algae resulting in clear blue conditions. Contrast with mesotrophic lakes, which have a moderate nutrient condition, and eutrophic lakes, which have excessive levels of nutrients.
What is ommatidium ?
A single unit, or visual section, of a compound eye such as that found in insects. It resembles a single simple eye that descends directly into the eye core. Each ommatidium contains a corneal lens, crystalline cone, and pigment and retinula cells and functions as a single eye sending an image to the brain. The insect’s brain must take all the messages from each ommatidia and piece the image together.
What is omnivore ?
An animal that eats both plant and animal material. Humans are omnivores.
What is oncogene ?
A normal cellular gene that, when inappropriately expressed or mutated, can transform eukaryotic cells into tumor cells. A gene that controls cell growth but also is responsible for directing the uncontrolled growth of tumor or cancer if it is damaged by means such as an inheritance defect, mutation, or environmental exposure such as to carcinogens. There are dozens of oncogenes known, and they function in a variety of ways, but their commonality is the overexpression that interferes with the normal regulation of cell growth.
What is ontogeny ?
The life history of one individual and its stages as it evolves from zygote to adult. The opposite of phylogeny, which is the history of a group.
What is oogamy ?
A process such as the fusion or union between a small motile or flagellated sperm (gamete) and large nonmotile egg (gamete).
What is oogenesis ?
The process and development of producing a female ovum; developing a diploid cell into a haploid egg.
What is open circulatory system ?
A type of circulatory system where the internal transport of blood flows through the body cavity and bathes the organs directly and not through a system of vessels. Humans have a closed circulatory system, which is a type of circulatory system where the blood flows through a system of ves sels and the heart. Examples include horseshoe crabs, lobsters, and insects.
What is operant conditioning ?
A type of associative learning behavior also called trial-and-error learning, or instrumental conditioning. It is a method to modify behavior (an operant) that utilizes contingencies between the response and the presentation of the reinforcer. Based on the 1938 experiments of Burrhus Friederich Skinner (rats pressing lever for food) and published in his book The Behavior of Organisms.
What is operon ?
A functional unit consisting of a PROMOTER, an operator, and a number of structural GENEs, found mainly in PROKARYOTEs. An example is the operon NIF. The structural genes commonly code for several functionally related ENZYMEs, and although they are transcribed as one (polycistronic) mRNA, each has its separate TRANSLATION initiation site. In the typical operon, the operator region acts as a controlling element in switching on or off the synthesis of mRNA.
Also refers to a group or sequence of closely linked genes that function as a unit in synthesizing enzymes needed for biosynthesis of a molecule and that is controlled by operator and repressor genes; common in bacteria and phages. An operator gene is the region of the chromosome, next to the operon, where a repressor protein binds to prevent transcription of the operon. The repressor gene protein binds to an operator adjacent to the structural gene, preventing the transcription of the operon.
What is opsonization ?
The modification of the surface of a bacterium by coating or deposition of an opsonin (an antibody or complement), which is a group of proteins that lyse organisms. An opsonin coats a bacterium in order to enhance its ability to be eaten (phagocytosis) by macrophages and other leukocytes; an immune response.
What is optically detected magnetic resonance (ODMR) ?
A double-resonance technique in which transitions between spin sublevels are detected by optical means. Usually these are sublevels of a triplet, and the transitions are induced by microwaves.
What is order ?
A taxonomic grouping between class and family. The order consists of groups that are more alike than those in a class.
What is organ ?
A specialized combination of two or more different tissues that performs a particular function. Several organs work together in an organ system to perform a set of coordinated functions. There are ten major organ systems in the human body, and each system is made up of one or more organs. These systems include the circulatory, digestive, endocrine, integumentary, muscular, nervous, reproductive, respiratory, skeletal, and urinary systems.
What is organelle ?
The “organs” of the cell. Any membranebound or nonmembrane-bound structure that is specialized in performing a specific role in the cell. Examples of organelles are chloroplasts, centrosomes, Golgi apparatus, ribosomes, mitochondria, and even the nucleus.
What is organic chemistry ?
The study of carbon (organic) compounds; used to study the complex nature of living things. Organic compounds are composed mostly of carbon, hydrogen, oxygen, and nitrogen atoms bonded together. One of two main divisions of chemistry. The other is inorganic chemistry. Branches of these two include analytical, biochemical, and physical chemistry.
What is organ of Corti ?
The organ within the cochlea that contains thousands of hairlike receptor cells that respond to different sound frequencies and convert them to nerve impulses through the auditory nerve to the brain.
What is organogenesis ?
The formation and advanced period of embryonic development of plants and animals when organs are formed from the primary germ layer. Its study is called organogeny.
What is orgasm ?
An involuntary and rhythmic contraction characterized by strong feelings of pleasure by both sexes during human sexual activity; the highest point of sexual excitement.
What is orphan drug ?
A DRUG for the treatment of a rare disease for which reasonable recovery of the sponsoring firm’s research and development expenditure is not expected within a reasonable time. The term is also used to describe substances intended for such uses.
What is osmoconformer ?
Not actively changing internal osmolarity (total solute concentration) because an animal is isotonic (body fluids are of equal concentration with respect to osmotic pressure) with the environment.
What is osmolarity ?
Solute concentration expressed as molarity. Molarity is the moles of solute dissolved in 1 liter of solution. A solute is, in the case of a gas or solid dissolved in liquid, the gas or solid, but in other examples it is the part that has the smaller amount. For example, a beaker of salt water would have the water as the solvent and the salt as the solute. The mole is defined as the number of carbon 12 atoms in 12 grams of carbon 12. It allows scientists to weigh substances and tell how many particles are in that substance.
What is osmoregulation ?
A process to control water balance in a cell or organism with respect to the surrounding environment using osmosis. The ability by which organisms maintain a stable solute concentration by maintaining osmotic pressure on each side of a semipermeable membrane.
What is osmoregulator ?
An organism that must take in or discharge excess water because its body fluids have a different osmolarity than the environment.
What is osmosis ?
The diffusion or movement of water across a selectively permeable membrane from one aqueous system to another of different concentration. Water moves from areas of high-water/low-solute concentration to areas of low-water/high-solute concentration.
What is osmotic pressure ?
Pressure that is generated by a solution moving by osmosis into and out of a cell and caused by a concentration gradient.
What is Osteichthyes ?
A class of fish—“bony fish”; Osteichthyes is the largest and most diverse taxon of all vertebrates. Found as early as the lower Devonian period, there are two subclasses, Actinopterygii (e.g., ray fin: sturgeon, tuna, catfish) and Sarcopterygii (fleshy fin: lungfish, coelacanths). Two of the most successful groups of vertebrates ever known, with some species adapted to breathe air. Their endoskeleton is made of bone.
What is osteoporosis ?
A decrease in bone mass and bone density with associated increased risk of fracture, especially of wrists, hips, and spines. Of the 10 million Americans estimated to have osteoporosis, 8 million are women and 2 million are men.
What is ostracoderm ?
A primitive and extinct fish without jaws and encased in an armor of bony plates and dermal scales. It lived from the early Ordovician to the late Devonian (470 to 370 million years ago). Also known as agnathans, fossils have been found in both North America and Europe. Pteraspids, cyathaspids, and amphiaspids are examples.
What is ostracods ?
Aquatic crustaceans with seven pairs of appendages, each specialized for different tasks, that live inside a calcified carapace made of two valves. Sexually dimorphic, i.e., males and females are different shapes. There are more than 50,000 named species.
What is outgroup ?
During a phylogenetic analysis, an outgroup is any group that is not included in the study group but is related to the group under study. Used for comparative purposes. An outgroup is chosen because it is related to the taxon under study, but it has an ancestor in a more distant past than the taxon being classified.
What is ovarian cycle ?
Determines the menstrual cycle in the ovary; a regular cyclic event that comprises two phases and ovulation: the follicular phase (before ovulation), ovulation itself, and the luteal phase (after ovulation but before a new follicular phase). It normally lasts for 11 to 16 days and is regulated by hormones.
What is ovary ?
The female organ or gonad, located on each side of the uterus, that produces oocytes that develop into mature eggs. The ovaries are connected by the fallopian tubes, also called the oviducts. They also produce female estrogens (estradiol and progesterone) that are responsible for secondary sexual characteristics.
What is oviduct ?
Another name for fallopian tubes, hollow organs about 12 centimeters long (about 6 inches) that join the ovary to the uterus and that transport the ovum.
What is oviparous ?
Refers to a process in which a female animal produces eggs that develop and hatch outside the body. In oviparous species, fertilization occurs when the sperm meet the ova as they pass through the oviduct. Insects such as butterflies and moths are oviparous. They lay their eggs on leaves in which the larvae hatch.
What is ovotransferrin ?
An iron-binding protein from eggs, structurally similar to the TRANSFERRINs.
What is ovoviviparous ?
Animals that reproduce by eggs that remain in the mother’s uterus until they are ready to hatch. The young emerge alive with only a membrane to break away from. There is no umbilical cord attached to a placenta. Some fish and reptiles are ovoviviparous.
What is ovulation ?
The process in which a mature ovary follicle opens and releases an egg (secondary oocyte) enclosed in a mucouslike material. In mammals, one egg is released each menstrual cycle.
What is ovule ?
A protective structure in seed plants where the female gametophyte develops, and where fertilization occurs. The integument, a layer of tissue, surrounds the ovule and it becomes a seed.
What is ovum ?
Alternative term for egg. It is the secondary oocyte in mammals. Unfertilized haploid nonmotile egg cell.
What is oxidase ?
An ENZYME that catalyzes the oxidation of SUBSTRATEs by O2.
What is oxidation ?
A process where one or more electrons are lost, and the oxidation state of some atom increases. It can occur only in combination with reduction, a process where electrons are gained and the oxidation state of some atom decreases.
What is oxidation number ?
The oxidation number of an element in any chemical entity is the number of charges that would remain on a given atom if the pairs of electrons in each bond to that atom were assigned to the more electronegative member of the bond pair. The oxidation number of an element is indicated by a roman numeral placed in parentheses immediately following the name (modified if necessary by an appropriate ending) of the element to which it refers. The oxidation number can be positive, negative, or zero. Zero, not a roman numeral, is represented by the usual cipher, 0. The positive sign is never used. An oxidation number is always positive unless the minus sign is explicitly used. Note that it cannot be nonintegral. Nonintegral numbers may seem appropriate in some cases where a charge is spread over more than one atom, but such a use is not encouraged. In such ambiguous cases, the charge number, which designates ionic charge, can be used. A charge number is a number in parentheses written without a space immediately after the name of an ion, and whose magnitude is the ionic charge. Thus the number may refer to cations or anions, but never to neutral species. The charge is written in Arabic numerals and followed by the sign of the charge.
In a COORDINATION entity, the oxidation number of the CENTRAL ATOM is defined as the charge it would bear if all the LIGANDs were removed along with the electron pairs that were shared with the central atom. Neutral ligands are formally removed in their closedshell configurations. Where it is not feasible or reasonable to define an oxidation state for each individual member of a group or CLUSTER, it is again recommended that the overall oxidation level of the group be defined by a formal ionic charge, the net charge on the coordination entity.
What is oxidative addition ?
The INSERTION of a metal of a COORDINATION entity into a covalent bond involving formally an overall two-electron loss on one metal or a one-electron loss on each of two metals.
What is oxidative phosphorylation ?
An aerobic process of energy harnessing by the production of ATP (energy) in mitochondria by enzymatic phosphorylation of ADP coupled to an electron transport chain (ETC). The ETC is a series of mitochondrial enzymes (protein carrier molecules) in the mitochondrial membranes. As high-energy electrons are shuttled down the chain via NADH and FADH2 (flavin adenine dinucleotide) to oxygen molecules, they produce ATP and water.
What is oxidizing agent ?
An atom or ion that causes another to be oxidized, and therefore the agent to become reduced. It is a reactant that accepts electrons from another reactant. Oxygen, chlorine, ozone, and peroxide compounds are examples of oxidizing agents.
What is oxidoreductase ?
An ENZYME of EC class 1, which catalyzes an oxidation-reduction reaction.
What is oxygen ?
One of the most important elements for biological systems and for other processes, such as reacting with other substances to release energy. One tree can produce enough oxygen in one week to meet the demands of a person’s daily oxygen need. Oxygen is needed in oxidation-reduction reactions within cells. Cellular respiration is the process that releases energy by breaking down food molecules in the presence of oxygen. Atomic symbol is O; atomic number is 8.
What is oxygen-evolving complex (OEC) ?
The ENZYME that catalyzes the formation of O2 in PHOTOSYNTHESIS. Contains a CLUSTER of probably four manganese ions. ozone (O3) A form of oxygen containing three atoms instead of the common two; formed by ultraviolet radiation reacting with oxygen. Ozone accounts for the distinctive odor of the air after a thunderstorm or around electrical equipment, first reported as early as 1785; ozone’s chemical constitution was established in 1872. The ozone layer in the upper atmosphere blocks harmful ultraviolet radiation that normally causes skin cancer. Ozone is an oxidizer and a disinfectant, and it forms hydrogen peroxide when mixed with water. The Earth’s ozone layer protects all life from the sun’s harmful radiation, but human activities have damaged this shield. The United States, in cooperation with over 140 other countries, is phasing out the production of ozone-depleting substances in an effort to safeguard the ozone layer.
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