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Estrella Mountain - Anatomy terms Category: Education > Body parts Date & country: 25/03/2011, USA Words: 586

mosaic evolution
A pattern of evolution where all features of an organism do not evolve at the same rate. Some characteristics are retained from the ancestral condition while others are more recently evolved.

motor (efferent) pathways
The portion of the peripheral nervous system that carries signals from the central nervous system to the muscles and glands.

motor neurons
Neurons that receive signals from interneurons and transfer the signals to effector cells that produce a response. Nerve cells connected to a muscle or gland. Sometimes also known as effector neurons.

motor output
A response to the stimuli received by the nervous system. A signal is transmitted to organs that can convert the signals into action, such as movement or a change in heart rate.

motor units
Consist of a motor neuron with a group of muscle fibers; form the units into which skeletal muscles are organized; enable muscles to contract on a graded basis.

mouth
The oral cavity; the entrance to the digestive system where food is broken into pieces by the teeth and saliva begins the digestion process.

mucus
A thick, lubricating fluid produced by the mucous membranes that line the respiratory, digestive, urinary, and reproductive tracts; serves as a barrier against infection and, in the digestive tract, moistens food, making it easier to swallow.

mutualism
A form of symbiosis in which both species benefit. A type of symbiosis where both organisms benefit. The classic example is lichens, which is a symbiosis between an alga and a fungus. The alga provides food and the fungus provides water and nutrients.

mycelium
The mass of interwoven filaments of hyphae in a fungus.

mycorrhiza
Occurs when a fungus (basidiomycete or zygomycete) weaves around or into a plant's roots and forms a symbiotic relationship. Fungal hyphae absorb minerals from the soil and pass them on to the plant roots while the fungus obtains carbohydrates from the plant (pl.: mycorrhizae).

myelin sheath
Layers of specialized glial cells, called Schwann cells, that coat the axons of many neurons.

nares
Nostrils; the openings in the nose through which air enters.

nastic movement
A plant's response to a stimulus in which the direction of the response is independent of the direction of the stimulus. Non-directional plant movements.

natural selection
The process of differential survival and reproduction of

nectaries
Nectar-secreting organs in

negative feedback control
Occurs when information produced by the feedback reverses the direction of the response; regulates the secretion of most hormones.

nektonic organisms
"Swimmers"; one of the two main types of organisms in the pelagic zone of the marine biome.

nephridium
The excretory organ in

nerve cord
A dorsal tubular cord of nervous tissue above the notochord of a chordate.

nervous system
One of eleven major body organ systems in animals; coordinates and controls actions of internal organs and body systems, receives and processes sensory information from the external environment, and coordinates short-term reactions to these stimuli. PICTURE 1 PICTURE 2 PICTURE 3

net primary productivity (NPP)
The rate at which producer (usually plants) biomass is created in a community.

neural tube
A tube of ectoderm in the embryo that will form the spinal cord.

neuromuscular junction
The point where a motor neuron attaches to a muscle cell.

niche
The biological role played by a species.

niche overlap
The extent to which two species require similar resources; speci

node
The stem region of a plant where one or more leaves attach. Where leaves are attached to stems.

node of Ranvier
A gap between two of the Schwann cells that make up an axon's myelin sheath; serves as a point for generating a nerve impulse.

nondisjunction
The failure of chromosomes to separate properly during cell division. The unequal segregation of chromosomes during meiosis. This forms cells with either too many (possibly one or more single or sets of chromosomes too many) or too few chromosomes. Thought to be a common cause for Down Syndrome, where sufferers often have an extra copy ...

notochord
In chordates, a cellular rod that runs the length of the body and provides dorsal support. Also, a structure of mesoderm in the embryo that will become the vertebrae of the spinal column. The stiff rod-like structure that all members of the Phylum Chordata develop at some stage during their life.

nuclear area
In prokaryotic cells, a region containing the cell's genetic information. Unlike the nucleus in eukaryotic cells, it is not surrounded by a membrane.

nucleic acids
Polymers composed of nucleotides; e.g., DNA and RNA.

nucleosomes
Spherical bodies formed by coils of chromatin. The nucleosomes in turn are coiled to form the

nucleus (atom)
An atom's core; contains protons and one or more neutrons (except hydrogen, which has no neutrons).

oils
Triglycerides that are liquid at room temperature.

oncogenes
Genes that can activate cell division in cells that normally do not divide or do so only slowly. A gene that when over-expressed leads to cancer, but which normally functions in cell division.

one gene one polypeptide hypothesis
A revision of the one gene, one enzyme hypothesis. Some proteins are composed of different polypeptide chains encoded by separate genes, so the hypothesis now holds that mutation in a gene encoding a specifc polypeptide can alter the ability of the encoded protein to function and thus produce an altered phenotype.

open community
A community in which the populations have different density peaks and range boundaries and are distributed more or less randomly.

opposable
The capability of being placed against the remaining digits of a hand or foot; e.g., the ability of the thumb to touch the tips of the fingers on that hand.

opsins
Molecules in cone cells that bind to pigments, creating a complex that is sensitive to light of a given wavelength.

organ systems
Groups of organs that perform related functions.

organism
An individual, composed of organ systems (if multicellular). Multiple organisms make up a population.

orgasm
Rhythmic muscular contractions of the genitals (sex organs) combined with waves of intense pleasurable sensations; in males, results in the ejaculation of semen.

osmoconformers
Marine organisms that have no system of osmoregulation and must change the composition of their body

osmoregulation
The regulation of the movement of water by osmosis into and out of cells; the maintenance of water balance within the body.

osmoregulators
Marine vertebrates whose body

osteoarthritis
A degenerative condition associated with the wearing away of the protective cap of cartilage at the ends of bones. Bone growths or spurs develop, restricting movement and causing pain.

osteoporosis
A disorder in which the mineral portion of bone is lost, making the bone weak and brittle; occurs most commonly in postmenopausal women.

out of Africa hypothesis
Holds that modern human populations (Homo sapiens) are all derived from a single speciation event that took place in a restricted region in Africa.

overkill
The shooting, trapping, or poisoning of certain populations, usually for sport or economic reasons.

ovum
The female gamete, egg.

oxytocin
A peptide hormone secreted by the posterior pituitary that stimulates the contraction of the uterus during childbirth.

ozone
A triatomic (O₃) form of oxygen that is formed in the stratosphere when sunlight strikes oxygen atoms. This atmospheric ozone helps

race
A subdivision of a species that is capable of interbreeding with other members of the species.

radially symmetrical
In animals, refers to organisms with their body parts arranged around a central axis. Such animals tend to be circular or cylindrical in shape.

radiation
Energy emitted from the unstable nuclei of radioactive isotopes.

ray-finned
Taxonomic group of fish, such as trout, tuna, salmon, and bass, that have thin, bony supports holding the

reabsorption
The return to the blood of most of the water, sodium, amino acids, and sugar that were removed during

recessive
Refers to an allele of a gene that is expressed when the dominant allele is not present. An allele expressed only in homozygous form, when the dominant allele is absent.

recombinant DNA molecules
New combinations of DNA fragments formed by cutting DNA segments from two sources with restriction enzyme and then joining the fragments together with DNA ligase. Interspecies transfer of genes usually through a vector such as a virus or plasmid.

recombinant DNA technology
A series of techniques in which DNA fragments are linked to self-replicating forms of DNA to create recombinant DNA molecules. These molecules in turn are replicated in a host cell to create clones of the inserted segments.

recombination
A way in which meiosis produces new combinations of genetic information. During synapsis, chromatids may exchange parts with other chromatids, leading to a physical exchange of chromosome parts; thus, genes from both parents may be combined on the same chromosome, creating a new combination.

reduction
The gain of an electron or a hydrogen atom. The gain of electrons or hydrogens in a chemical reaction.

reflex
A response to a stimulus that occurs without conscious effort; one of the simplest forms of behavior.

renin
An enzyme secreted by the kidneys that converts angiotensinogen into angiotensin II.

reproductive isolating mechanism
Biological or behavioral characteristics that reduce or prevent interbreeding with other populations; e.g., the production of sterile hybrids. Establishment of reproductive isolation is considered essential for development of a new species.

resolution
In relation to microscopes, the ability to view adjacent objects as distinct structures.

resource partitioning
The division of resources such that a few dominant species exploit most of the available resources while other species divide the remainder; helps explain why a few species are abundant in a community while others are represented by only a few individuals.

respiratory surface
A thin, moist, epithelial surface that oxygen can cross to move into the body and carbon dioxide can cross to move out of the body.

resting potential
The difference in electrical charge across the plasma membrane of a neuron.

restriction enzymes
A series of enzymes that attach to DNA molecules at speci

retina
The inner, light-sensitive layer of the eye; includes the rods and cones.

rheumatoid arthritis
A crippling form of arthritis that begins with in

rhizoids
Filamentous structures in the plants group known as bryophytes that attach to a substrate and absorb moisture. The term is also applied to similar structures found outside the bryophytes.

rhizome
In ferns, a horizontal stem with upright leaves containing vascular tissue.

rods
Light receptors in primates' eyes that provide vision in dim light.

salivary amylase
An enzyme secreted by the salivary glands that begins the breakdown of complex sugars and starches.

salivary glands
Glands that secrete salvia into the mouth.

saprophytes
Organisms that obtain their nutrients from decaying plants and animals. Saprophytes are important in recycling organic material.

sapwood
Layers of secondary xylem that are still functional in older woody plants; visible as the outer lighter areas in the cross section of a tree trunk.

secondary cell wall
In woody plants, a second wall inside the primary cell wall; contains alternating layers of cellulose and lignin.

secondary compounds
Plant products that are not important in metabolism but serve other purposes, such as attracting animals for pollination or killing parasites.

secondary immunity
Resistance to an antigen the second time it appears. Because of the presence of B and T memory cells produced during the

secondary macronutrients
Elements that plants require in relatively small quantities: calcium, magnesium, and sulfur.

secretion
The release of a substance in response to the presence of food or speci

sedimentary rock
Any rock composed of sediment, i.e., solid particles and dissolved minerals. Examples include rocks that form from sand or mud in riverbeds or on the sea bottom.

segments
Repeating units in the body parts of some animals.

selective breeding
The selection of individuals with desirable traits for use in breeding. Over many generations, the practice leads to the development of strains with the desired characteristics.

sensor
In a closed system, the element that detects change and signals the effector to initiate a response.

sensory (afferent) pathways
The portion of the peripheral nervous system that carries information from the organs and tissues of the body to the central nervous system.

sensory input
Stimuli that the nervous system receives from the external or internal environment; includes pressure, taste, sound, light, and blood pH.

sensory neurons
Neurons that carry signals from receptors and transmit information about the environment to processing centers in the brain and spinal cord. Neurons carrying messages from sensory receptors to the spinal cord. Sometimes referred to as an afferent neuron.

sex linkage
The condition in which the inheritance of a sex chromosome is coupled with that of a given gene; e.g., red-green color blindness and hemophilia in humans. Traits located on the X-chromosome.

short-day plants
Plants that

sink
A body or process that acts as a storage device or disposal mechanism; e.g., plants and the oceans act as sinks absorbing atmospheric carbon dioxide. Also, a location in a plant where sugar is being consumed, either in metabolism or by conversion to starch.

sleep movement
In legumes, the movement of the leaves in response to daily rhythms of dark and light. The leaves are horizontal in daylight and folded vertically at night.

smog
A local alteration in the atmosphere caused by human activity; mainly an urban problem that is often due to pollutants produced by fuel combustion.

social behavior
Behavior that takes place in a social context and results from the interaction between and among individuals.

societies
The most highly organized type of social organization; consist of individuals that show varying degrees of cooperation and communication with one another; often have a rigid division of labor.

somatic nervous system
The portion of the peripheral nervous system consisting of the motor neuron pathways that innervate skeletal muscles.

somatic senses
All senses except vision, hearing, taste, and smell; include pain, temperature, and pressure.