10Th Chem O

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obligate aerobe aorganism that needs oxygen in order to live

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obligate aerobe

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obligate anaerobe an organism that needs the absence of oxygen in order to live

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obligate anaerobe

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observation the process of obtaining information by using the senses; the information obtained by using the senses

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observation

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occluded front a front that forms when a cold air mass overtakes a warm air mass and lifts the warm air mass off the ground and over another air mass

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occluded front

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ocean current a movement of ocean water that follows a regular pattern

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ocean current

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ocean floor the surface of the ocean basin

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ocean floor

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ocean floorthe 7 to 10 km thick layer of sediment and igneous rock that makes up the ocean floor

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ocean floor

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oceanography the scientific study of the ocean, including the properties and movements of ocean water, the characteristics of the ocean floor, and the organisms that live in the ocean

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oceanography

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ocean thermal energy conversion the use of temperature differences in ocean water to produce electricity (abbreviation, OTEC)

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ocean thermal energy conversion

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ocean trench a long, narrow, and steep depression on the ocean floor that forms as when one tectonic plate subducts beneath another plate; trenches run parallel to volcanic island chains or to the coastlines of continents; also called a trench or a deep-ocean trench

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ocean trench

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octane number a measure of a fuel’s burning efficiency and antiknock properties

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octane number

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octet rule a concept of chemical bonding theory that is based on the assumption that atoms tend to have either empty valence shells or full valence shells of eight electrons

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octet rule

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oil reserves oil deposits that are discovered and are in commercial production

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oil reserves

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olfactory bulb the part of the brain that is found at the end of the olfactory nerve and that serves as the center of the sense of smell in vertebrates

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olfactory bulb

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olfactory cell one of the nerve cells that produce the sensation of smell

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olfactory cell

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olfactory nerve the nerve that carries impulses from the olfactory receptors to the brain

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olfactory nerve

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a cell found in the nasal passages that is stimulated by certain substances, produces nerve impulses, and gives rise to the sense of smell

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olfactory receptor

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oligotrophic lake a lake that lacks plant nutrients and that has a lot of oxygen dissolved in its lower layer

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oligotrophic lake

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omnivore an organism that eats both plants and animals

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omnivore

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oncogene a gene that induces cancer, or uncontrolled cell proliferation

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oncogene

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oogenesis the production, growth, and maturation of an egg, or ovum

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oogenesis

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oogonium a single-celled gametangium (female sex organ) in some algae and fungi

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oogonium

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Oort cloud a spherical region that surrounds the solar system, that extends from just beyond Pluto's orbit to almost halfway to the nearest star, and that contains trillions of comets

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Oort cloud

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ooze a soft mud at the bottom of a lake, river, or estuary

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ooze

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opaque describes an object that is not transparent or translucent; a material through which light cannot pass

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opaque

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open circulatory system a type of circulatory system in which the circulatory fluid is not contained entirely within vessels; a heart pumps fluid through vessels that empty into spaces called sinuses

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open circulatory system

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open cluster a group of stars that are close together relative to surrounding stars

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open cluster

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open-pit mining a method of mining that is used to remove ores and minerals near the surface and in which the ore is broken and loaded after the waste is removed

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open-pit mining

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open system a system that can exchange both matter and energy with its surroundings

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open system

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open-water zonethe zone of a lake or pond that extends from the littoral zone out across the top of the water and that is only as deep as light can reach through the water

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open-water zone

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operating system the software that controls a computer's activities

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operating system

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operator a short sequence of viral or bacterial DNA to which a repressor binds to prevent transcription (mRNA synthesis) of the adjacent gene in an operon

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operator

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operculum in fish, a hard plate that is attached to each side of the head, that covers gills, and that is open at the rear

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operculum

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operon a unit of gene regulation and transcription in bacterial DNA that consists of a promoter, an operator, and one or more structural genes

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operon

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opportunistic infection an infection caused by a microorganism that normally does not cause disease but that becomes pathogenic if the patient's immune system is weakened

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opportunistic infection

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optical fiber a transparent thread of plastic or glass that transmits light

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optical fiber

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optic nerve the nerve that connects the retina of the eye to the brain and that transmits impulses that contribute to the sense of sight

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optic nerve

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oral groove a depressed region around the mouth of some ciliate protozoans, such as Paramecium

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oral groove

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oral surface the surface of a radially symmetrical animal, such as an echinoderm, on which the mouth is located

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oral surface

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orbit the path that a body follows as it travels around another body in space

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orbit

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orbital a region in an atom where there is a high probability of finding electrons

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orbital

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orbital period the time required for a body to complete a single orbit

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orbital period

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orbital velocity the speed and direction that an object must have to remain in an orbit

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orbital velocity

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order in chemistry, a classification of chemical reactions that depends on the number of molecules that appear to enter into the reaction

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order

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order the taxonomic category below the class and above the family

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order

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order numberthe number assigned to interference fringes relative to the central bright fringe

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order number

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ore a natural material whose concentration of economically valuable minerals is high enough for the material to be mined profitably

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ore

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ore mineral a mineral that contains one or more elements of economic value

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ore mineral

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organ a collection of tissues that carry out a specialized function of the body

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ore mineral

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organelle one of the small bodies that are found in the cytoplasm of a cell and that are specialized to perform a specific function

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organelle

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organic compound a covalently bonded compound that contains carbon, excluding carbonates and oxides

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organic compound

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sedimentary rock that forms from the remains of plants or animals

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organic sedimentary rock

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organism a living thing; anything that can carry out life processes independently

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organism

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organ of Corti in the ear, a structure that is located in the cochlea and that contains hair cells that are the sensory receptors for hearing

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organ of Corti

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organ system a group of organs that work together to perform body functions

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organ system

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origin in anatomy, the point at which a muscle attaches to a stationary bone

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origin

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ornithologist a person who specializes in the scientific study of birds

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ornithologist

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osculum an opening in a sponge's body through which water exits

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osculum

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osmosis the diffusion of water or another solvent from a more dilute solution (of a solute) to a more concentrated solution (of the solute) through a membrane that is permeable to the solvent

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osmosis

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osmotic pressure the external pressure that must be applied to stop osmosis

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osmotic pressure

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ossicle one of the small, calcium carbonate plates that make up the endoskeleton of an echinoderm

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ossicle

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ossification the process by which cartilage is converted into bone

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ossification

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osteoarthritisadegenerative joint disease

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osteoarthritis

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osteocyte a bone cell

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osteocyte

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ostium one of the small openings in a sponge’s body through which water enters

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ostium

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outcrop an area of exposed rock

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outcrop

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outer core the liquid layer of the Earth’s core that lies beneath the mantle and surrounds the inner core

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outer core

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outer ear the part of the ear that collects sound vibrations

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outer ear

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outwash plain a broad sheet of sand and gravel deposited in front of a glacier by meltwater streams

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outwash plain

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oval window the membrane that separates the middle ear from the inner ear

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oval window

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ovarian cycle a series of hormone-induced changes in which the ovaries prepare and release a mature ovum each month

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ovarian cycle

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ovary in the female reproductive system of animals, an organ that produces eggs

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ovary

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ovaryin flowering plants, the lower part of a pistil that produces eggs in ovules

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ovary

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overgrazing the depletion of vegetation due to the continuous feeding of too many animals

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overgrazing

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overharvesting catching or removing from a population more organisms than the population can replace

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overharvesting

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overpopulationa condition that occurs when the number of individuals within an environment becomes so large that there are not enough resources to support them all

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overpopulation

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oviduct the tube that leads from an ovary to the uterus

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oviduct

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oviparous describes organisms that produce eggs that develop and hatch outside the body of the mother

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oviparous

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ovipositor in many female insects, a structure that is at the end of the abdomen and that is used to lay eggs

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ovipositor

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ovoviviparous describes organisms that produce eggs that develop and hatch inside the body of the mother

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ovoviviparous

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ovulation the release of an ovum from a follicle of the ovary

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ovulation

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ovule a structure in the ovary of a seed plant that contains an embryo sac and that develops into a seed after fertilization

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ovule

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ovum a mature egg cell

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ovum

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oxbow lake a lake that forms when a stream cuts a new channel across the narrow neck of a meander

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oxbow lake

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oxidation a reaction that removes one or more electrons from a substance such that the substance's valence or oxidation state increases; in geology, the process by which a metallic element combines with oxygen

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oxidation

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oxidation number the number of electrons that must be added to or removed from an atom in a combined state to convert the atom into the elemental form

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oxidation number

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oxidation reactioa chemical reaction in which a reactant loses one or more electrons such that the reactant becomes more positive in charge

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oxidation reaction

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reaction oxidation-reductionany chemical change in which one species is oxidized (loses electrons) and another species is reduced (gains electrons); also called redox reaction

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reaction oxidation-reduction

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oxidation state the condition of an atom expressed by the number of electrons that the atom needs to reach its elemental form

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oxidation state

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oxidized describes an element that has lost electrons and that has increased its oxidation number

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oxidized

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oxidizing agentthe substance that gains electrons in an oxidation-reduction reaction and that is reduced

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oxidizing agent

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oxygen debt the extra oxygen taken in by the body while recovering from exercise

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oxygen debt

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oxytocin a hormone that stimulates milk production and uterine contractions

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oxytocin

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ozone a gas molecule that is made up of three oxygen atoms

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ozone

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ozone hole a thinning of stratospheric ozone that occurs over the poles during the spring

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ozone hole

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ozone layer the layer of the atmosphere at an altitude of 15 to 40 km in which ozone absorbs ultraviolet solar radiation

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ozone layer