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| Term | Definition |
|---|---|
| absorption | the process in which nutrients enter cells of the villi, then move across the cells and enter blood vessels. |
| acids | compounds that release hydrogen ions (H+) when the compounds are placed in water. |
| actin | a protein filament within the sarcomeres of muscle cells. |
| action | potential occurs when a neuron is displaying a nerve impulse. |
| active site | the portion of an enzyme that interacts with the substrate. |
| active transport | the movement of molecules across a membrane from a region of low concentration to a region of high concentration that requires the expenditure of energy (ATP). |
| adenosine diphosphate (ADP) | a product of adenosine triphosphate (ATP) breakdown. |
| adenosine triphosphate (ATP) | the chemical substance that serves as the currency of energy in cells. |
| adrenal glands | two glands lying atop the kidneys that produce a family of steroids. |
| aerobic | organisms that require oxygen for their metabolism. |
| algae | a large number of photosynthetic organisms that are generally unicellular and not classified as plants. |
| alleles | different forms of the same gene. |
| alveoli | microscopic air sacs that are surrounded by a rich network of blood vessels in mammalian lungs that function in gas exchange; the air sacs are at the end of the bronchioles. |
| amino acids | the building blocks of proteins. |
| amoeba | single-celled organisms with no distinct shape; members of the phylum Sarcodina. |
| anabolism | the process of synthesizing large molecules by joining smaller molecules together. |
| anaerobic | organisms that thrive in an oxygen-free environment. |
| anaphase | a phase during mitosis in which chromatids separate to become visible chromosomes and migrate to opposite poles. |
| anaphase I | a phase during meiosis in which homologous chromosomes separate. |
| anaphase II | a phase during meiosis II in which the centromeres divide and the chromosomes separate from one another. |
| androgens | hormones, such as testosterone, produced from the testes that promote secondary male characteristics. |
| Animalia | the kingdom that includes the animals. |
| antibodies | proteins synthesized by plasma cells that are released into the circulation to the antigen site and destroy the microorganisms by chemically reacting with them. |
| antibody-mediated immunity | the process by which antibodies bind to antigens and destroy the microorganisms in a highly specific manner. |
| anticodon | the complementary codon present on a tRNA molecule. |
| antigens | the immune-stimulating polysaccharides on the surface of cells. |
| aorta | the major artery of the human circulatory system that receives blood from the left ventricle. |
| appendix | a small fingerlike process that may be a vestige of larger organs functional in human ancestors. |
| archaebacteria | ancient bacteria that have a different ribosomal structure, membrane composition, and cell wall composition than modern bacteria. |
| arteries | the channels through which fluid flows away from the heart. |
| atom | the smallest part of an element that can enter into various combinations with atoms of other elements. |
| atrium | a thin-walled receiving chamber in which blood accumulates in fishes. |
| auditory nerve | the nerve within the ear that carries impulses to the brain for interpretation. |
| autonomic nervous system | a subdivision of the peripheral nervous system, which is divided into the sympathetic and parasympathetic nervous systems. |
| autosomes | the 22 pairs of human chromosomes that are not sex chromosomes. |
| autotrophic | certain bacteria that synthesize their own foods. |
| axon | the long extension of a neuron. |
| bacilli | the rod-shaped bacteria (singular, bacillus). |
| bark | the structure of vascular plants formed between the phloem and the cork. |
| bases | compounds that attract hydrogen atoms when placed in water. |
| basophils | the white blood cells that function in allergic responses. |
| bicuspid (mitral) valve | the valve that leads into the left ventricle of the human heart. |
| binomial | name the scientific name of an organism, which contains two elements. |
| biomass | the total dry weight of food at each level of the food pyramid. |
| biome | a group of communities dominated by a particular climax community, such as deserts, forests, and prairies. |
| biosphere | the blanket of living things that surrounds the substratum of the earth. |
| blastocyst | a hollow ball of cells resulting after the morula has passed through the Fallopian tubes and enters the female uterus. |
| blood clotting | the process in which platelets adhere to the walls of damaged blood vessels, setting off a series of processes leading to the formation of a patchy mesh at the injury site. |
| blue-green algae | cyanobacteria; members of the kingdom Monera that are photosynthetic and are found in the soil and in freshwater or saltwater environments. |
| B lymphocytes | white blood cells within the lymph nodes; stimulated by microorganisms or other foreign materials in the blood. |
| Bowman's capsule | an enlarged cuplike structure below the nephron in the human kidney. |
| bronchi | two large tubes at the lower end of the trachea (singular, bronchus). |
| bronchioles | the branches formed from the bronchi. |
| capillaries | the microscopic blood vessels between the arteries and the veins. |
| carbohydrates | the primary energy source for living things; composed of carbon, hydrogen, and oxygen. |
| cardiac muscle | the involuntary muscle found in the heart; contains actin and myosin filaments. |
| carnivores | animals that eat other animals. |
| carrying capacity | a situation when a population has reached the maximum size that the environment can support. |
| catabolism | the breakdown or digestion of large, complex molecules. |
| cecum a blind sac that is the meeting point of the small and large intestines. | |
| cerebellum | a portion of the hindbrain that serves as a coordinating center for motor activity. |
| cell body | the main portion of the nerve cell. |
| cell cycle | many repetitions of cellular growth and reproduction; divided into interphase and mitosis. |
| cell-mediated immunity | the process in which the T lymphocytes interact with the microorganisms cell-to-cell and destroy them. |
| cells | the fundamental units of living things. |
| cellular respiration | the process by which animals and other organisms obtain the energy available in carbohydrates. |
| cell wall | a strong membrane outside the plasma membrane present in certain cells, such as bacteria and plants. |
| centriole | a cylinder-like organelle that assists in chromosomal migration during mitosis. |
| centromere | the place of attachment of the two homologous chromatids during prophase in mitosis. |
| cerebrum | the portion of the forebrain that controls higher mental activity, such as learning, memory, logic, creativity, and emotion. |
| cervix | the opening at the lower end of the uterus. |
| chemiosmosis | the subdivision of cellular respiration in which the energy given off by electrons is used to pump protons across a membrane and synthesize ATP. |
| chemoreceptors | the specialized receptor cells that transmit smell and taste. |
| chlorophyll | green pigment that makes up a photosystem that absorbs energy from the sun during photosynthesis. |
| chloroplast | an organelle within green plants in which photosynthesis occurs. |
| chordates | animals with rods along their backs, including reptiles, amphibians, birds, and mammals. |
| chromatid | homologous chromosomes joined to each other at the centromere; present during the prophase of mitosis. |
| chromatin | compacted DNA and protein. |
| chromosomes | linear units of DNA. |
| chyme | a soupy liquid formed in the stomach from the churning of the bolus with gastric juices. |
| circulatory system | the transport system in animals. |
| class | a grouping of similar orders. |
| cocci | spherical bacteria (singular, coccus). |
| cochlea | a snail-like series of coiled tubes within the skull that assist hearing. |
| coenzymes | organic molecules that act as cofactors, such as NAD and FAD. |
| cofactors | ions or molecules that associate with enzymes and are required for enzymatic reactions to take place. |
| commensalism | a relationship in which one population receives a benefit from an association while the other is neither benefited nor harmed. |
| community | a situation in which populations of organisms each contain a habitat and a niche. |
| comparative anatomy | comparing the anatomical structures of modern day organisms with fossils to yield clues to the type of organisms that roamed earth long ago. |
| comparative biochemistry | the comparison of biochemical processes of modern day organisms with fossils and ancient species; modern biochemistry indicates there is a biochemical similarity in all living things. |
| compound | a collection of molecules. |
| cone cells | cells of the eye that detect color. |
| consumers | the organisms within an ecosystem that meet their energy needs by feeding on the producers. |
| cork | a tough tissue that combines with the phloem to become the bark of vascular plants. |
| coronary arteries | the arteries that supply the heart muscle with blood. |
| corpus luteum | the mass of cells derived from the female follicle that secretes progesterone. |
| cortex | the outer portion of the adrenal gland. |
| corticosteroids | the steroids secreted from the adrenal glands. |
| cristae | the folds of the inner mitochondrial membrane. |
| crossing over | a process during prophase I in which segments of DNA from one chromatid in the tetrad pass to another chromatid in the tetrad. |
| cyanobacteria | see blue-green algae. |
| cytochromes | molecules that accept and release electrons in an electron transport system. |
| cytokinesis | the process during mitosis in which the cytoplasm divides into two separate cells; also called cytoplasmic division. |
| cytoplasm | semiliquid substance that composes the foundation of the cell and contains the organelles. |
| cytoskeleton | an organelle within cells consisting of an interconnected system of fibers, threads, and interwoven molecules that give structure to the cell. |
| cytosol | see cytoplasm. |
| decomposers | the organisms of decay; usually bacteria and fungi. |
| dendrites | the short extensions of the neuron. |
| deoxyribonucleic | acid see DNA. |
| deoxyribose | the five-carbon carbohydrate attached to purine or pyrimidine bases within DNA molecules. |
| dermal tissue | the tissue that functions to protect the plant from injury and water loss and covers the outside of the plant. |
| diffusion | the movement of molecules through a membrane from a region of high concentration to low concentration. |
| diploid | cells having two sets of chromosomes. |
| diploid | nuclei contained within a mass of cytoplasm within cellular slime molds. |
| disaccharides | sugars composed of two molecules. |
| division | see phylum. |
| DNA | deoxyribonucleic acid; a double helix nucleotide molecule containing deoxyribose, nitrogenous base, and a phosphate group; contains the genetic information from which amino acids are determined. |
| DNA fingerprinting | a technique that uses electrophoresis to match DNA molecules to one another for identification purposes. |
| DNA polymerase | the enzyme that joins all the nucleotide components to one another to form a long strand of nucleotides. |
| DNA replication | the process by which cells replicate or synthesize their DNA; takes place during S phase of the cell division cycle. |
| domestic breeding | a process of directed evolution that brings about new forms that differ from ancestral stock. |
| dominant | an allele that expresses itself. |
| ductless glands | glands that have no ducts, such as the endocrine glands. |
| duodenum | the first 10 to 12 inches of the small intestine in which most of the chemical digestion takes place. |
| eardrum | the tympanic membrane that receives vibrations from the outer ear. |
| ecosystems | systems formed from the interactions between communities and their physical environments. |
| ectoderm | one of three germ layers that develops into the skin and nervous system. |
| egg | the haploid cell within the female ovary. |
| elements | the fundamental building blocks of matter within all living things. |
| embryo | forms when all the organs of the body have taken shape. |
| embryology | the study of embryonic development. |
| endergonic reaction | chemical reactions in which energy is obtained and trapped from the environment. |
| endocrine glands | glands throughout the animal body that secrete hormones, which help coordinate body systems. |
| endocytosis | the process in which a small patch of plasma membrane encloses particles that are near the cell surface. |
| endoderm | one of three germ layers that develops into the gastrointestinal tract. |
| endoplasmic reticulum (ER) | an organelle comprised of a series of membranes extending throughout the cytoplasm; two types exist, rough and smooth ER. |
| endoskeleton | an internal support system in the echinoderms and most vertebrates that may include a framework of bones and cartilage that serves as a point of attachment for muscle. |
| endosperm | the female tissue that encloses the seed within the angiosperms. |
| entropy | the degree of disorder or randomness of a system. |
| environmental fitness | an individual's ability to adapt to an environment and reproduce. |
| enzymes | proteins that catalyze the chemical reactions within cells. |
| eosinophils | white blood cells whose functions are uncertain. |
| epididymis | the tube in which sperm cells mature. |
| epiglottis | a thin flap of tissue that folds over the opening to the mammalian trachea during swallowing and prevents food from entering the trachea. |
| epinephrine | a hormone produced in the adrenal medulla that increases heart rate, blood pressure, and the blood supply to skeletal muscle. |
| erythrocytes | the red blood cells; disk-shaped cells produced in the bone marrow that have no nucleus; their cytoplasm is filled with hemoglobin to transport oxygen. |
| erythropoetin | a hormone produced by the kidney cells that functions in the production of red blood cells. |
| esophagus | a thick-walled muscular tube located behind the windpipe that extends through the neck and chest to the stomach. |
| estrogen | a hormone produced by the ovaries that stimulates the development of secondary female characteristics. |
| eubacteria | modern bacteria. |
| eukaryotes | cells that contain a nucleus and internal cellular bodies called organelles. |
| evolution | changes that occur within populations and organisms that make individuals able to adapt to their external environment. |
| exergonic reaction | a chemical reaction in which energy is released. |
| exocrine glands | glands, such as the salivary glands, that deliver their enzymes via ducts. |
| exoskeleton | the hard, protective, outer covering of arthropods and mollusks. |
| facilitated diffusion | the movement of molecules across a membrane from a region of high concentration to a region of low concentration that is assisted by proteins. |
| Fallopian tubes | the passageways that egg cells enter after release from the ovaries; also called oviducts. |
| family | similar genera classified together. |
| fats | lipids composed of a glycerol and fatty acids. |
| fatty acids | long chains of carbon atoms with carboxyl groups at one end. |
| feeding pattern | the pattern in which animals obtain their nutrients. |
| fermentation | an anaerobic process in which energy can be released from glucose even though oxygen is not available; occurs in yeast cells. |
| fertilized egg cell | an egg cell that has been fertilized by a sperm cell. |
| fetus | results from a developing embryo at about eight weeks when the embryo is somewhat human looking and the remaining development consists chiefly of growth and maturation. |
| flavin adenine dinucleotide (FAD) | a coenzyme that functions in the production of ATP. |
| food chain | the transfer of food energy from producers to consumers. |
| food pyramid | a way of expressing the availability of food in an ecosystem at a successive number of trophic levels. |
| food web | many interwoven food chains. |
| forebrain | a portion of the brain that consists of the cerebrum, thalamus, hypothalamus, and limbic system. |
| Fungi | a kingdom that includes the yeasts, molds, mildews, and mushrooms. |
| G1 phase | a phase within interphase of the cell division cycle that prepares cells for DNA replication. |
| G2 phase | a phase within interphase of the cell division cycle that prepares cells for mitosis. |
| gametes | sex cells of parent organisms; usually haploid cells. |
| gastrin | a hormone produced by digestive glands to influence digestive processes. |
| gene | the functional segment of chromosomes. |
| gene flow | a mechanism of evolution that results when individuals migrate from one group to another and contribute their genes to the gene pool of the new population. |
| gene linkage | the concept of transfer of a linkage group. |
| gene linkage map | a map that pinpoints the location of genes based on their connection to certain marker gene sequences. |
| gene pool | the collection of genes within a population; as changes in the gene pool occur, a population evolves. |
| genetic drift | a mechanism of evolution that occurs when a small group of individuals leaves a population and establishes a new one in a geographically isolated region. |
| genome | the set of all genes that specify an organism's traits. |
| genotype | the gene composition of a living organism. |
| genus | a grouping of similar species (plural, genera). |
| geographic distribution | the distribution of species in geographical areas. |
| geotropism | the turning of a plant away from or toward the earth. |
| gills | structures that allow fish to exchange gases with their environment. |
| glial cells | the cells of the nervous system that support, protect, and nourish the neurons. |
| glomerulus | a ball of capillaries that comprises Bowman's capsule in the human kidney. |
| glottis | a slitlike structure at the opening to the mammalian trachea. |
| glucagon | a hormone produced in the pancreas that stimulates the breakdown of glycogen to glucose in the liver. |
| glucose | a carbohydrate with the chemical formula C6H12O6 that serves as the primary carbon source of living things. |
| glycogen | a polysaccharide composed of thousands of glucose units that serves as the storage form of glucose in the human liver. |
| glycolysis | the subdivision of cellular respiration in which glucose molecules are broken down to form pyruvic acid molecules. |
| Golgi apparatus | an organelle within eukaryotic cells comprised of a series of flattened sacs; the site of protein and lipid processing and packaging; also called Golgi bodies. |
| Graafian follicle | a cluster of cells within the ovary that is derived from egg cells and secretes female hormones called estrogens. |
| ground tissue | the tissue of the vascular plant that is responsible for storing the carbohydrates produced by the plant. |
| gymnosperms | vascular plants having naked seeds, such as the conifers. |
| haploid | cells containing one copy of each chromosome. |
| hemoglobin | a red pigment that binds oxygen and carbon dioxide molecules and carries them through the bloodstream. |
| herbivores | animals that eat plants. |
| heterotrophic | species that acquire food from organic matter. |
| heterozygous | two different alleles that are present for a particular characteristic. |
| hindbrain | the portion of the brain that consists of the medulla, pons, and cerebellum. |
| histones | nuclear proteins that coil DNA molecules. |
| homeostasis | the process in which the internal environment exists at a steady-state equilibrium despite changes in the external environment. |
| homeothermic | animals that can maintain a constant body temperature. |
| homozygous | two identical alleles that are present for a particular characteristic. |
| hormones | biochemical substances produced within plant or animal cells, or glands, that exert a particular effect. |
| hydrostatic skeleton | a water-based skeleton present in many animals (such as the earthworm) that lack structures, such as bone, for muscles to pull against. |
| hypothalamus | the portion of the forebrain that serves as the control center for hunger, thirst, body temperature, and blood pressure. |
| hypothesis | the proposal of a solution to the question within the scientific method. |
| ileum | the final 12 feet of the small intestine. |
| immune response | the stimulation of B and T lymphocytes. |
| incomplete dominance | an allele combination in which two characteristics blend and both alleles can express themselves; one example is red, white, and pink snapdragons. |
| inner cell mass | a group of cells that continues to develop at one end of the blastocyst. |
| interneuron | a type of neuron that connects sensory and motor neurons and carries stimuli in the brain and spinal cord. |
| interphase | the cell division cycle phase in which the cell spends most of its time; includes G1, S phase (DNA replication), and G2. |
| invertebrates | the most primitive of the chordates; lack a backbone. |
| involuntary muscle | see smooth muscle and cardiac muscle. |
| islets of Langerhans | clusters of cells that make up the endocrine portion of the pancreas. |
| jejunum | the second 10 inches of the small intestine. |
| kinetochore | a region of DNA that has remained undivided during prophase of mitosis; binds to the spindle fibers that eventually pull apart the sister chromatids. |
| kingdom | the largest and broadest category of the classification system. |
| Krebs cycle | the subdivision of cellular respiration in which pyruvic acid is broken down and the energy in its molecules is used to form high-energy compounds. |
| larynx | the voicebox of mammals, formed from several folds of cartilage at the upper end of the trachea. |
| left atrium | the chamber of the human heart that receives oxygen-rich blood via the pulmonary vein. |
| left ventricle | the chamber of the human heart in which oxygen-rich blood enters through the bicuspid valve that leads into the aorta. |
| lens | the portion of the eye that focuses the light on the retina. |
| leukocytes | the white blood cells produced in the bone marrow that have various functions in the body, such as immune reaction. |
| lichens | associations between the cyanobacteria and the fungi. |
| ligaments | the tough, fibrous tissues that link bones to one another. |
| limbic system | a collection of structures that ring the edge of the brain and apparently function as centers of emotion. |
| lipid | an organic molecule used to form cellular and organelle membranes, the sheaths surrounding nerve fibers, and certain hormones; includes fats as an energy source. |
| liver | the organ that helps to process the products of human digestion and removes excess glucose from the bloodstream, converting it to a polymer called glycogen for storage. |
| loop of Henle | the segment of the human kidney after the proximal tubule. |
| lungs | the organ where oxygen diffuses into the blood to join with hemoglobin in the red blood cells. |
| lymph | a watery fluid derived from plasma that seeps out of the blood system capillaries and mingles with the cells. |
| lymph nodes | capsule-like bodies that contain cells that filter the lymph and phagocytize foreign particles. |
| lymphatic system | the extension of the circulatory system consisting of capillaries called lymph vessels, a fluid called lymph, and structures called lymph nodes. |
| lymphatic vessels | a series of vessels that return the lymph fluid to the circulatory system. |
| lymphocytes | the white blood cells that are essential components of the immune system. |
| lysosome | an organelle within eukaryotic cells; a droplike sac filled with enzymes used for digestion within the cell. |
| mammals | milk-producing animals. |
| marsupials | the mammals whose embryos develop within the mother's uterus for a short period of time before birth. |
| medulla | the inner portion of the adrenal glands; a swelling at the tip of the hindbrain that serves as the passageway for nerves extending to and from the brain. |
| meiosis | the process by which the chromosome number is halved during gamete formation. |
| menstruation | the process by which the endometrium is released in females. |
| meristematic tissue | the growth tissue; the location of most cell division of vascular plants. |
| mesoderm | one of three germ layers that develops to become the muscles and other internal organs. |
| metabolism | the rapid turnover of chemical materials; involves the release or use of chemical energy. |
| metaphase | the stage during mitosis in which the pairs of chromatids line up on the equatorial plate. |
| metaphase I | the phase during meiosis in which tetrads align on the equatorial plate (as in mitosis). |
| metaphase II | the phase during meiosis II in which the chromatid pairs gather at the center of the cell prior to separation. |
| midbrain | a portion of the brain that lies between the hindbrain and the forebrain that consists of a collection of crossing nerve tracts. |
| minerals | types of nutrients that include phosphorus, sulfur, potassium, magnesium, and zinc. |
| mitochondrion | the organelle that is the site of energy production in eukaryotic cells. |
| molecule | a precise arrangement of atoms of different elements. |
| Monera | the kingdom that includes the bacteria and the cyanobacteria; prokaryotic organisms. |
| monocytes | some of the white blood cells that function in phagocytosis. |
| monosaccharides | sugars that are composed of single molecules. |
| monotremes | the egg-laying mammals that produce milk. |
| morula | a solid mass of cells that develops about six days after fertilization of an egg cell. |
| motor neuron | a type of neuron that transmits impulses from the brain and spinal cord to muscles or glands. |
| mRNA | messenger RNA; the RNA molecules that receive the genetic code in the DNA and carry the code into the cytoplasm where protein synthesis takes place. |
| multiple alleles | a condition in which more than two alleles exist for a characteristic; one example is A, B, AB, and O blood types. |
| muscle contraction | a process in which actin and myosin proteins move within a sarcomere. |
| mutation | a random change in the gene pool of a population that gives rise to new alleles and is the source of variation in a population. |
| mutualism | a living arrangement in which both partners benefit. |
| myelin sheath | a fatty layer of material that covers the axons of nerve cells. |
| myofibrils | microscopic filaments that make up a muscle cell. |
| myosin | a protein microfilament that comprises the sarcomere of muscle cells. |
| natural selection | the concept that random, small variations take place in living things that lead to the gradual development of a species. |
| nephron | the functional and structural unit of the kidney that produces urine and is the primary unit of homeostasis in the human body. |
| nerve chord | also called a spinal cord; a hollow structure that extends the length of the animal just above the notochord. |
| nerve impulse | an electrochemical event that occurs within the neuron. |
| nerve roots | the 31 pairs of projections that extend out along each side of the spinal cord; the sites of axons of the sensory and motor neurons. |
| nerves | bundles of axons bound together. |
| neuroglia | the glial cells together with the extracellular tissue. |
| neuron | a nerve cell. |
| neurotransmitter | a chemical substance that accumulates in the synapse and increases the membrane permeability of the next dendrite. |
| neutrophils | the white blood cells that function in phagocytosis. |
| nicotinamide adenine dinucleotide (NAD) | a coenzyme that functions during respiration to produce ATP. |
| nicotinamide adenine dinucleotide phosphate (NADP) | a coenzyme that functions during photosynthesis to produce ATP. |
| nitrogenous base | the nitrous molecules that make up DNA (and RNA) molecules; two major types are purines and pyrimidines. |
| nonvascular plants | the plants that do not have specialized tissues to transport fluids. |
| norepinephrine | a hormone produced in the adrenal medulla that intensifies the effects of epinephrine. |
| notochord | a flexible rod of tissue extending the length of an animal that provides internal support. |
| nucleic acids | large molecules comprised of nucleotides. |
| nucleoli | the small organelles that make up the nucleus; the site for ribosomal synthesis, assembly, and packaging (singular, nucleolus). |
| nucleotide | the unit that makes up nucleic acid; contains a nitrogen base, a phosphate group, and a carbohydrate molecule. |
| nucleus | the organelle within eukaryotic cells that contains the genetic material, DNA. |
| Okazaki fragments | new sections of DNA that are placed along the lagging strand during DNA replication and are joined together by DNA ligase to produce a new DNA strand. |
| olfactory nerve | the nerve that carries the impulse from the nose to the brain for interpretation. |
| omnivores | animals that consume both plants and animals. |
| oocytes | the developed oogonia in a female after the age of puberty. |
| oogonia | primitive egg cells that accumulate in the ovaries before a female is born. |
| optic nerve | the nerve that carries impulses from the eye to the brain. |
| order | a grouping of similar families. |
| organelles | microscopic bodies within the cytoplasm that perform distinct functions. |
| osmosis | the movement of water molecules across a membrane from a region of high concentration to a region of low concentration. |
| ovary | an endocrine gland that secretes estrogens. In plants, the structure of the pistil where the ovules are enclosed. |
| oviducts | see Fallopian tubes. |
| ovulation | the process by which an egg cell is released from the follicle and swept into the Fallopian tube where it moves toward to uterus. |
| ovules | the protective structures that contain egg cells produced by the female. |
| Pacinian corpuscles | the touch and pain receptors on the skin, muscles, and tendons. |
| paleontology | the science of locating, cataloging, and interpreting the life forms that existed in past millennia. |
| pancreas | a large, glandular organ lying near the stomach that produces many of the enzymes used to digest food. |
| parasites | organisms that attack living things and cause disease. |
| parasitism | a type of symbiosis in which one population benefits while the other is harmed. |
| parasympathetic nervous system | a subdivision of the autonomic nervous system that returns the body to normal after an emergency. |
| parathyroid glands | glands located on the posterior surfaces of the thyroid gland that produce parathyroid hormone. |
| pathogenic | organisms that cause human disease. |
| PCR | polymerase chain reaction; a technique used to amplify a gene of interest. |
| peptides | small proteins. |
| peripheral nervous system | a collection of nerves that connect the brain and spinal cord to other parts of the body and the external environment. |
| peristalsis | a rhythmic series of muscular contractions that propels the bolus along. |
| peroxisome | cytoplasmic body containing enzymes for digestion. |
| phagocytes | cells that attack and engulf invading microorganisms. |
| phagocytosis | occurs when the vesicle formed from endocytosis contains particulate matter; the process by which cells or microorganisms are engulfed by another cell. |
| pharynx | the cavity at the rear of the mouth that the nasal chambers open into; the throat. |
| phenotype | the expression of genes and the physical characteristics that result. |
| phloem | structures of vascular plants that transport sugars and other nutrients from the leaves to the other parts of the plant. |
| phosphate group | a group derived from a molecule of phosphoric acid that connects the DNA molecules to one another. |
| phosphate ion | a product of adenosine triphosphate (ATP) together with ADP. |
| photosystem | the site within the chloroplast in which sunlight is captured; includes the pigment molecules, proton pumps, enzymes, coenzymes, and cytochromes. |
| phototropism | the bending and turning of the plant stem toward a light source. |
| phyla | related classes grouped together (singular, phylum). |
| physical map | a map that locates a gene of interest precisely by showing the actual number of base pairs between genes on a chromosome. |
| pineal gland | a human endocrine gland in the midbrain that regulates mating behaviors and day-night cycles. |
| pinocytosis | when the vesicle formed from endocytosis contains droplets of fluid. |
| pistil | the structure of the flower that contains a stigma, a style, and an ovary. |
| pith | the structure at the center of the stem of vascular plants. |
| pituitary gland | a gland at the base of the brain consisting of the anterior and posterior lobes that secretes several hormones. |
| placenta | the structure that supplies the fetus with nourishment. |
| placental mammals | mammals that have a nutritive connection between the embryo and the mother's uterine wall. |
| plant hormones | hormones that regulate the growth and development of many plants. |
| plasma | a straw-colored liquid composed primarily of water; the fluid portion of blood. |
| plasma cells | large antibody-producing cells derived from B lymphocytes when stimulated. |
| plasma membrane | also called a cell membrane; a membrane composed of lipids, proteins, and phospholipids. |
| plasmid | small circular DNA molecules often used as vectors to transform specific genes into cells. |
| platelets | small disk-shaped blood fragments produced in the bone marrow that serve as the starting material for blood clotting. |
| polygenic inheritance | the condition in which some characteristics are determined by an interaction of genes on several chromosomes or at several places on one chromosome; one example is human skin color. |
| polymerase chain reaction | see PCR. |
| polysaccharides | complex carbohydrates formed by linking multiple monosaccharides. |
| pons | the portion of the hindbrain below the medulla and the midbrain that acts as a bridge between various portions of the brain. |
| population | an interbreeding group of individuals of one species occupying a defined geographic area. |
| predation | a relationship in which one population within a community may capture and feed upon another population. |
| producers | organisms within an ecosystem that trap energy (by photosynthesis). |
| progesterone | a hormone produced by the corpus luteum that regulates the buildup of tissue in the endometrium and inhibits the contractions of the uterus. |
| prokaryotes | cells that do not contain a nucleus or internal organelles; include bacteria, cyanobacteria, and archaebacteria. |
| prophase | the first phase of mitosis; involves chromosomal condensation, nuclear membrane breakdown, and the migration of centrioles to opposite poles. |
| prophase I | the first phase of meiotic division, during which crossing over takes place. |
| prophase II | the phase during meiosis II in which the chromatin material condenses and each chromosome contains two chromatids attached by the centromere. |
| prostaglandins | the hormones secreted by various tissue cells that produce their effects on smooth muscles, on various glands, and in reproductive physiology. |
| proteinoids | the primitive polymers formed by the unison of amino acids; able to act as enzymes and catalyze organic reactions. |
| proteins | long chains of amino acid units that are the main molecules from which living things are constructed. |
| Protista | a kingdom that includes protozoa, one-celled algae, and slime molds. |
| protocells | the first cells. |
| protons | positively charged particles within the nucleus of an atom. |
| pulmonary artery | the artery of the human circulatory system that pumps the blood from the right ventricle to the lungs for gas exchange. |
| pulmonary vein | the vein of the human circulatory system that returns oxygen-rich blood from the lungs to the left atrium. |
| purine | a type of nitrogenous base present in DNA molecules containing two fused rings of carbon and nitrogen atoms; two examples in DNA are adenine (A) and guanine (G). |
| Purkinje fibers | the nerves that transfer amplified impulses to regions of the heart to control its function. |
| pyrimidine | a type of nitrogenous base in DNA molecules that has one ring containing carbon and nitrogen atoms; two examples in DNA are cytosine (C) and thymine (T). |
| recessive | the allele overshadowed by the dominant allele. |
| recombinant DNA | DNA molecules that have been altered in some way during the process of genetic engineering or biotechnology. |
| red blood cells | also known as erythrocytes; cells that contain hemoglobin to transport oxygen. |
| reflex arc | the simplest unit of nervous activity; involved in the detection of a stimulus in the environment by sensory nerve endings, followed by impulses that travel via the sensory neurons to the spinal cord. |
| renal arteries | arteries in which blood enters the kidney. |
| renal veins | veins in which blood exits the kidney. |
| responsiveness | the ability of living things to respond to stimuli in the external environment. |
| resting potential | the inactive state of a neuron in which the cytoplasm is negatively charged with respect to the outside of the cell. |
| restriction enzymes | catalyze the opening of a DNA molecule at a "restriction" point; many leave dangling ends of DNA molecules at the point where the DNA has been opened. |
| retina | a single layer containing nerve cells within the eye. |
| RFLP | restriction fragment length polymorphism; a technique using small bits of DNA fragments linked to various diseases. |
| rhodopsin | a light-sensitive pigment of the eye that functions in the detection of light. |
| ribonucleic acid s | ee RNA. |
| ribosomes | organelle bodies that may be bound to the ER that are the sites of protein synthesis in eukaryotic cells; the bodies in which amino acids are bound together to form proteins. |
| right atrium | the chamber of the human heart in which oxygen-poor blood enters through a major vein called the vena cava. |
| right ventricle | the pumping chamber of the human heart from which blood exits. |
| RNA | ribonucleic acid; a nucleic acid produced during transcription that is complementary to a DNA strand; similar to DNA in structure but contains the carbohydrate ribose and the pyrimidine uracil rather than thymine. |
| RNA polymerase | the enzyme that moves along the DNA strand, reads the nucleotides one by one, and synthesizes a complementary mRNA molecule according to the principle of complementary base pairing. |
| rod cells | the cells of the eye that permit vision in dim light. |
| roots | the structures of vascular plants that anchor them to the ground and take in water and minerals from the soil. |
| rough endoplasmic reticulum | ER studded with ribosomes; the site of protein synthesis in eukaryotic cells. |
| rRNA | ribosomal RNA; RNA molecules that function to manufacture ribosomes. |
| salivary glands | the parotid glands, the submaxillary glands, and the sublingual glands that secrete saliva into the mouth. |
| sarcolemma | the muscle cell membrane. |
| sarcomere | the functional unit of the muscle that contains thin actin filaments and thick myosin filaments. |
| scientific method | an orderly process of gaining information about the biological world. |
| scrotum | a pouch outside the male body that contains the testes. |
| secretin | a hormone produced by digestive glands that influences digestive processes. |
| seedless vascular plants | the division Pteridophyta that includes the ferns. |
| semen | a fluid secretion containing sperm and secretions from the prostate gland, seminal vesicles, and Cowper's glands. |
| semilunar valves | two valves found in the pulmonary artery and the aorta. |
| seminiferous tubules | coiled passageways in which sperm production takes place. |
| sensory neurons | neurons that receive stimuli from the external environment. |
| sensory somatic system | a subdivision of the peripheral nervous system that carries impulses from the external environment and the senses. |
| sepals | modified leaves that enclose and protect a growing bud in flowers. |
| serum | plasma from which clotting proteins have been removed. |
| sex chromosomes | one pair among the 23 pairs of human chromosomes; the X and Y chromosomes. |
| skeletal muscle | see striated muscle. |
| slime molds (cellular) | amoebalike cells that live independently and unite with other cellular slime molds to form a single, large, flat cell with many nuclei. |
| slime molds (true) | single, flat, very large cells with many nuclei. |
| small intestine | the site of chemical digestion; includes the duodenum, jejunum, and ileum. |
| smooth endoplasmic reticulum | ER with no ribosomes attached. |
| smooth muscle | found in the linings of the blood vessels, along the gastrointestinal tract, in the respiratory tract, and in the urinary bladder; contains few actin and myosin filaments; also called involuntary muscle. |
| species | a group of individuals that share features and are able to interbreed under natural conditions to yield fertile offspring. |
| spermatogonia | primitive cells within the seminiferous tubules that undergo a series of changes and then meiosis to yield sperm cells. |
| sperm cells | haploid cells within the male testes. |
| S phase | the phase within the cell division cycle in which DNA is replicated. |
| spinal cord | the white cord of tissue passing through the bony tunnel made by the vertebrae. |
| spiracles | a series of openings on the body surface of terrestrial arthropods that open into tiny air tubes that assist in gas exchange. |
| spirilla | flexible spiral bacteria (singular, spirillum). |
| spirochetes | rigid spiral bacteria. |
| spleen | the site where red blood cells are destroyed; a reserve blood supply for the body. |
| stamen | the structure of a flower that contains a thin, stemlike filament and an anther. |
| stomata | the pores within leaves surrounded by guard cells that regulate the rate of gas exchange, which regulates the rate of photosynthesis. (Singular, stoma.) |
| striated muscle | skeletal muscle fiber that appears to be banded due to the presence of overlapping actin and myosin filaments; also called voluntary muscle. |
| substrate | the substance changed or acted on by an enzyme. |
| survival of the fittest | the concept of natural selection that states that the fittest survive and spread their traits through a population. |
| sutures | the immovable joints where bones come together within the skull. |
| symbiosis | the relationship between two populations that live together in a close, permanent, and mutually beneficial association. |
| sympathetic nervous system | a subdivision of the autonomic nervous system that prepares the body for an emergency. |
| synapse | the fluid-filled space separating the end of the axon from the dendrite of the next neuron or from a muscle cell. |
| synergism | a type of relationship in which two populations accomplish together what neither could accomplish on its own. |
| telophase | a phase during mitosis in which the chromosomes arrive at the opposite poles of the cell. |
| telophase I | the phase during meiosis in which the nucleus reorganizes as the chromosomes become chromatin; cytoplasmic division takes place, resulting in two cells. |
| telophase II | the phase during meiosis II in which the chromosomes gather at the poles of the cells and form a mass of chromatin; the nuclear envelope develops, the nucleoli reappear, and the cells undergo cytokinesis. |
| tendons | the connective tissue by which muscles are attached to bones. |
| testes | endocrine glands that secrete androgens; the male reproductive organs located in the scrotum. |
| thalamus | a portion of the forebrain that integrates sensory impulses. |
| theory | a hypothesis that is confirmed through repeated experimentation. |
| thrombocytes | the starting material for blood clotting; also called platelets. |
| thylakoids | membranes that make up the grana in chloroplasts; the actual site of photosynthesis within chloroplasts. |
| thymosins hormones | secreted by the thymus gland that influence the development of the T lymphocytes of the immune system. |
| thymus gland | an endocrine gland in the neck tissues that secretes thymosins. |
| thyroid gland | a gland at the base of the neck that produces several hormones, such as thyroxine and calcitonin. |
| T lymphocytes | white blood cells in the lymph nodes that are stimulated by microorganisms or other foreign material in the blood. |
| trachea | the windpipe of mammals. |
| tracheae | the branching network that extends from holes to all parts of an anthropod body to assist in gas exchange. |
| tracheids | the main conducting vessels of the xylem in most vascular plants. |
| tracheophytes | vascular plants composed of a xylem and phloem. |
| transcription | the process in which a complementary strand of mRNA is synthesized according to the nitrogenous base code of DNA. |
| transgenic animals | animals in which one or more genes have been introduced into the nonreproductive cells. |
| translation | the process by which the genetic code is transferred to an amino acid sequence in a protein. |
| tricuspid valve | a valve that passes blood from the right atrium into the right ventricle. |
| tRNA | transfer RNA; RNA molecules in the cytoplasm of a cell that carry amino acids to the ribosomes for protein synthesis. |
| trophoblast | a layer of cells that forms after fertilization; projections from the trophoblast form vessels, which merge with maternal blood vessels to form the placenta. |
| tropism | the bending or turning response of a plant caused by external stimuli. |
| turgor pressure | the pressure exerted on a plant's guard cells to open. |
| umbilical cord | the source of attachment of the fetus to the maternal blood supply. |
| urea | a component of urine that results from amino acid breakdown in the liver. |
| ureters tubes | that carry waste from the kidneys to the urinary bladder for storage or release. |
| urethra | the path in which urine flows from the bladder to the exterior; the tube within the penis that carries the sperm. |
| uric acid | a component of urine that results from nucleic acid breakdown. |
| urinary bladder | the site where waste products are shipped from the kidney for storage or for release. |
| urine | the product of the kidney; a watery solution of waste products, salts, organic compounds, uric acid, and urea. |
| uterus | a muscular organ in the pelvic cavity of female mammals; also called the womb. |
| vacuole | an organelle found in mature plant cells that stores nutrients and toxic waste. |
| vagina | a muscular organ in female mammals leading from the cervix to the exterior. |
| vascular bundles | arrangements of the xylem and phloem in vascular plants. |
| vascular plants | plants that contain specialized tissues to transport fluids. |
| vascular plants with protected seeds angiosperms | the most developed and complex vascular plants. |
| vascular plants with unprotected seeds gymnosperms | vascular plants that contain naked seeds, such as the conifers. |
| vectors | the carriers of DNA genes to be inserted into cells. |
| veins | channels through which fluid flows toward the heart. |
| vena cava | the major vein in the human heart; pumps oxygen-poor blood into the right atrium. |
| ventricle | a pumping chamber for blood to exit from the heart. |
| vertebrates | animals with backbones. |
| vessels | the main conducting vessels of the xylem found in the angiosperms. |
| virus | fragments of nucleic acid surrounded by a protein coat; may attack cells and replicate within the cells, destroying them. |
| vitamins | organic nutrients essential in trace amounts to the health of animals. |
| voluntary muscle | see striated muscle. |
| white blood cells | see leukocytes. |
| xylem | the structure of vascular plants that conducts water and minerals upward from the roots. |
| zygote | a fertilized egg cell, which is diploid. |
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sadham
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