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A abiotic factors: nonliving physical features of the environment, including soil, water, temperature, air, light, wind, and minerals. acid rain: rain or snow with a pH below 5.6; formed when water vapor reacts with sulfur oxides and nitrogen oxides in the air to form strong acids. active transport: movement of material through a cell membrane with the use of energy. adaptation: any characteristic of an organism that makes it better able to survive in its environment. anaerobe: organism that can survive without oxygen. angiosperm: a flower-producing vascular plant in which the seed is enclosed in a fruit, such as an apple. antibiotic: a substance produced by an organism that is used to kill or inhibit another organism. antibiotic resistance: in bacteria, the evolutionary change that occurs when bacterial strains that are mostly killed by a specific drug mutate into strains that are not affected by that drug. aerobe: organism that must have oxygen to survive. antibody: a protein made by the body in response to a specific antigen. aggression: a forceful act used to dominate or control another animal. antigens: proteins and chemicals that are foreign to the body. algae: plantlike protists that contain chlorophyll and make their own food; they have no roots, stems, or leaves and live in or near water. antiseptic: a substance that kills pathogens on living tissue and helps prevent their regrowth. allele: a different form a gene may have for a trait. anus: an opening at the end of the digestive tract through which solid wastes leave the body. alternation of generations: in some protists and in plants, a continuous cycle that alternates between sporophyte and gametophyte generations. alveoli: in the lungs, clusters of tiny, thin walled air sacs at the end of each bronchiole, where oxygen and carbon dioxide are exchanged. amino acids: the building blocks of proteins. amniotic egg: in reptiles, the leathery egg that provides a complete environment for the developing embryo. amniotic sac: a thin membrane that forms around an embryo, filled with amniotic fluid (a clear liquid that cushions the embryo). amphibian: ectothermic vertebrate that spends part of its life in water and part on land; examples are frogs, toads, and salamanders. appendage: a structure growing from the body, such as an arm or a leg. archaebacteria: prokaryotic, one-celled organisms that live as anaerobes in extreme environments, including salt ponds, hot sulfur springs, and deep ocean thermal vents. artery: a thick, elastic-walled vessel that moves blood away from the heart. Arthropoda: largest animal phylum, classified by the number of body segments and appendages; includes insects, shrimp, spiders, and centipedes. ascus: the small, saclike structure in which sac fungi produce spores. asexual reproduction: a type of reproduction in which a new organism is produced from one parent. bladder: the bag-shaped, elastic, muscular organ that stores urine until it leaves the body; can hold up to 500mL of urine. atherosclerosis: a circulatory system disorder in which fatty deposits form on artery walls and restrict blood flow. blood pressure: the force exerted by blood on the walls of the vessels; pressure is highest in the arteries and in young adults is normally 120 over 80. atria: the two up[per chambers of the human heart. auxin: a plant hormone that causes plant stems and leaves to grow or bend toward light. axon: neuron structure that carries messages away from the cell body. B basidium: the club-shaped, spore-producing structure of club fungi. behavior: the way an organism acts toward its environment. bilateral symmetry: describes animals with body parts arranged in the same way on both sides of their body. bog: low-lying, spongy, wet ground compressed mainly of dead plants, whose decay has been slowed by lack of oxygen. brain stem: the part of the brain extending from the cerebrum to the spinal cord; controls and coordinates involuntary muscle movements such as heartbeats. bronchi: two short tubes that branch off the trachea and carry air into the lungs (singular: bronchus). budding: a type of asexual reproduction in which a new organism grows off the side of its parent. C binomial nomenclature: the two-word naming system that provides every organism with its own scientific name. cambium: vascular plant tissue that produces new xylem and phloem cells. biological indicator: species whose health reflects the health of its ecosystem. cancer: a major chronic disease resulting from uncontrolled cell growth. biomass: organic material from plants or animals that is used for energy. capillary: a microscopic blood vessel that connects arteries and veins; nutrients, oxygen, and wastes are exchanged through their onecell-thick walls. biomes: large geographic areas that have similar climates and ecosystems. biosphere: all parts of Earth where life exists, including air, land, and water. biotechnology: a method of improving crops by moving DNA directly from one organism to another. biotic factors: living organisms in the environment, such as plants and animals. captive breeding: the breeding of an endangered species in captivity. carbohydrate: a nutrient that provides move of the body’s energy; made up of carbon, hydrogen, and oxygen. cardiac muscle: involuntary muscle tissue found only in the heart. carnivore: an animal that eats only other animals. carrying capacity: the largest number of individuals that an environment can support and maintain over time. cartilage: a thick, tough, smooth flexible tissue that is harder than flesh but softer than bone (like your ears); it covers the ends of bones to allow movement and cushion shock. cell: the smallest unit of an organism that can perform life functions. cell membrane: the selectively permeable outer boundary of a cell that allows food and oxygen to move into the cell and wastes to leave it. cell theory: a major theory of life science: the cell is the basic unit of life; organisms are made up of one or more cells; and all cells come from other cells. cell wall: in plants, the rigid structure made of cellulose that surrounds a plant cell membrane and supports and protects it. central nervous system: part of the body’s control system, including the brain and spinal cord; sorts and interprets information from stimuli. cerebellum: the part of the brain that coordinates voluntary muscle movements: maintains balance and muscle tone. cerebrum: the part of the brain that interprets impulses from the senses, stores memory, and controls the work of voluntary muscles. chemical digestion: chemical breakdown of food by fluids in the mouth, stomach, and small intestine; breaks down large molecules into smaller ones that can be absorbed by cells. chemotherapy: the use of chemicals to destroy cancer cells. chloroplasts: plant cell organelles in which light energy is changed into chemical energy in the form of sugar during the process of photosynthesis. chordate: a member of the animal phylum Chordata that has a notochord, a dorsal hollow nerve cord, and gill slits at some time in its life cycle. chromatin: hereditary material in a cell’s nucleus; chromatin coils into the form of chromosomes when a cell divides. chromosome: threadlike strands of DNA and protein in a cell nucleus that carry the code for the cell characteristics of an organism. chronic disease: a noncommunicable disease, such as diabetes or cancer, that lasts a long time. cilia: short, hairlike structures that extend from the cell membrane and help tiny organisms move; found in respiratory passages. circadian rhythm: behavior on a 24-hour cycle. class: third highest taxonomic category, below phylum (animals) or division(plants). classify: to group ideas, information, or objects based on their similarities. climax community: the final stage of a community’s ecological succession; it is stable, with a balance of abiotic and biotic factors. clinical trial: a test performed on volunteers, typically to test medicines, before the products are made available to the public. clone: an individual that is genetically identical to one of its parents. closed circulatory system: a type of bloodcirculation system in which vessels transport blood to the internal organs, as in humans. cnidarians: a phylum of hollow-bodied animals with stinging cells. collar cells: in sponges, the lining cells that help water move through the sponge by the beating of flagella. dermis: the inner layer of skin; it contains many blood vessels, nerves, and sweat and oil glands. commensalism: a symbiotic relationship that benefits one partner but not the other. desert: the driest biome on Earth; supports little plant life and receives less than 25 cm of rain yearly. communicable disease: a disease that is transmitted from one organism to another by pathogenic bacteria, viruses, and fungi. communication: an exchange of information among animals by means of cries, movements, touch, speech, pheromones, and so on. community: all the populations of different species that live in the same place at the same time and interact with each other. compound light microscope: an instrument that uses light and convex lenses to magnify objects. consumers: organisms that can’t make their own food. contour feathers: on birds, the strong, lightweight feathers that are used for flight and that give birds their coloring and sleek shape. control: in an experiment, the standard for comparison. coronary circulation: the flow of blood to heart tissues. crop: in an earthworm, a sac in the digestive system that stores soil. cuticle: a waxy protective layer on the stems and leaves of land plants that helps the plant conserve water. cytoplasm: the gel-like substance inside the cell membrane that contains structures that carry out life processes. D dendrite: neuron structure that receives messages and sends them to the cell body. development: all the changes undergone by living things as they grow. diaphragm: a muscle beneath the lungs that helps move air in and out of the body. dichotomous key: a detailed list of traits used to identify a specific organism. diffusion: the movement of molecules from areas of greater concentration to areas of lesser concentration. digestion: the process that breaks down food into small molecules that can be moved into the blood and used by the cell. disinfectant: a substance that kills pathogens on non-living objects. division: second-highest taxonomic category in the plant and fungi kingdoms. DNA: deoxyribonucleic acid; a chemical in the nuclei of cells that codes and stores genetic information; consists of strands of molecules that control cell activities using coded instructions. dominant: the form of a trait that appears to dominate or mask another form of the same trait. dorsal hollow nerve cord: a tubular bundle of nerves that lies above the notochord in a chordate animal; the spinal cord in most vertebrates. down feathers: on birds, the soft, fluffy insulating feathers that cover their skin. E echinoderm: a spiny skinned invertebrate that lives on the bottom of the ocean and that moves by means of a water-vascular system. endocytosis: a process by which cells transport a large body, such as a large protein molecule, through a cell membrane into the cytoplasm. ecological pyramid: a model used to describe the transfer of energy through a community. endoplasmic reticulum (ER): a cell organelle consisting of folded membranes that move materials around within the cell. ecological succession: the process of gradual change from one community of organisms to another. endoskeleton: the internal skeleton of an organism that supports and protects the internal organs and provides a frame for muscle. ecology: the study of relationships between organisms and between organisms and their physical environment. endospore: a tick walled structure that some bacteria produce around themselves, especially for protection from heat and drought. ecosystem: a community interacting with the nonliving (abiotic) parts of its environment. ectotherm: vertebrate animal whose internal body temperature changes with its environment. egg: in organisms that reproduce sexually, the sex cell (gamete) from the female parent. electron microscope: an instrument that bends beams of electrons in a magnetic field; magnifies objects too small to be seen with a light microscope. embryo: a fertilized egg during early growth; in humans, an unborn child during the first two months of pregnancy. embryology: the study of the development of embryos, which are the earliest stage of an organism’s development. emphysema: a respiratory disease in which the alveoli in the lungs lose their ability to expand and contract, mostly caused by smoking. endangered species: a species with so few individuals left that it is in danger of extinction. endotherm: vertebrate animal that maintains a constant body temperature. enzyme: a protein that speeds chemical reactions in cells without being changed itself. epidermis: the surface or outer layer of our skin. equilibrium: condition in which molecules of substance are spread evenly throughout a space. erosion: the wearing away of soil by wind, water, and ice. estivation: an adaptation for survival in hot, dry weather during which an animal becomes inactive and all body processes slow down. estuary: the areas where a freshwater river or stream meets the ocean. ethics: the process that applies right and wrong to people and their actions. eubacteria; prokaryotic, one-celled organisms found everywhere; reproduce by fission; include pathogenic bacteria and cyanobacteria. evidence: information that is gathered by direct observation. evolution: changes that occur over time in the hereditary features of a species of organisms. flagellum: a whiplike tail on bacteria and some protists that helps them move through a moist environment. exocytosis: a process by which a cell moves large molecules out through the cell membrane. food chain: a model used to show how energy from food passes from one organism to another. exoskeleton: on all arthropods, the hard, lightweight external covering that shields, supports, and protects the body. food web: a model used to describe a series of overlapping food chains. extinction: the dying out of an entire species. F fossil fuel: a fuel created over time from the bodies of once-living organisms; coal, oil, and natural gas. fossils: remains of life from an earlier time. family: the fifth-highest taxonomic category, below an order. fat: a nutrient that provides energy; also cushions organs and helps the body absorb some vitamins. free-living: describes an organism that finds its own food and place to live without depending on another organism; the opposite of a parasite. function: the specific task something does. fermentation: a form of respiration that converts energy from glucose when the supply of oxygen is not sufficient; yeast and some bacteria use alcohol fermentation to release energy and carbon dioxide. fertilization: in organisms that reproduce sexually, the fusion of an egg and sperm. fetus: a developing embryo. filter feeder: an organism that obtains food and oxygen by filtering it from the water from which it lives. fin: fanlike structure on most fish; adapted for steering, balancing, and moving through the water. fish: a ectothermic vertebrate whose gills, fins, and scales adapt it to living in water. fission: a type of asexual reproduction used by bacteria in which one bacterium divides to form two cells with identical genetic material. G gametophyte: the sex cell-producing stage of a plants life cycle. gene: the segment of DNA on a chromosome that directs the making of a specific protein, thus controlling traits that are passed to offspring. genetic engineering: biological and chemical methods to change a cell’s DNA sequence to produce desirable traits or eliminate undesirable traits. genetics: the science of how traits are inherited through alleles passed from one generation to another. genome: a map of the location of individual genes on every chromosome of an individual. genotype: the genetic makeup of an organism for a trait. genus: a group of different organisms with similar characteristics; can have one or more species. geothermal energy: heat energy from below Earth’s surface. gestation period: the time between fertilization and birth, during which the embryo develops in the uterus. gill: organ that exchanges carbon dioxide with water. gill slits: pair openings in the throat; in fish, they develop into gills for breathing underwater. gizzard: in an earthworm, a muscular digestive structure that grinds soil. H habitat: the physical location where an organism lives. hazardous waste: harmful or poisonous waste material. heart murmur: a defect in the heart caused by an improperly functioning valve. hemoglobin: a chemical in red blood cells that carries oxygen to tissues, carries carbon dioxide to lungs, and gives blood its red color. global warming: the potential warming of Earth due to an increase in greenhouse gases in the atmosphere. herbivore: an animal that eats only plants. Golgi bodies: cell organelles consisting of stacks of membrane-covered sacs that package and move proteins to the outside of the cell. hermaphrodite: an animal that produces both sperm and eggs. gradualism: a model of evolution, showing a steady, slow, and continuous change of one species into new species. grassland: a biome dominated by climax communities of grasses but that, due to a dry season, does not have forests. greenhouse effect: the process by which heat radiated from Earth’s surface is trapped and reflected back to Earth by gases in the atmosphere, causing worldwide temperatures to increase. groundwater: water in the soil or trapped in underground rock pockets. guard cells: in a plant leaf, cells that surround the stomata to open and close them. gymnosperm: a vascular plant that produces seeds on the scales of female cones, such as pinecones. heredity: passing of traits from parent to offspring. heterozygous: an organism that has two different alleles for a trait. hibernation: an adaption for winter survival during which an animal becomes inactive and all body processes slow down. homeostasis: the regulation of steady, lifemaintaining conditions inside an organism or cell, despite changes in its environment. homologous: body parts in different species that are similar in origin and structure. homozygous: an organism that has two identical alleles for a trait. hormones: chemicals secreted from endocrine glands that control specific body activities. host cell: a living cell in which a virus reproduces. hydroelectric power: energy source that uses the power of flowing water to produce electricity. hyphae: the mass of many-celled, threadlike tubes that form the body of a fungus. hypothesis: a prediction that can be tested. I immune system: a complex group of defenses that the body uses to fight disease. incomplete dominance: the production of a phenotype in an offspring that is intermediate to the phenotypes of its two homozygous parents. inference: a logical conclusion based on your observations. informed consent: a form volunteers sign that states that they have been told about the risks and that they agree to participate in the trial. insulin: substance produced by the islets of Langerhans to help body cells use glucose in the blood for energy. interneurons: nerve cells throughout the brain and spinal cord that transmit impulses from sensory neurons to motor neurons. intertidal zone: the part of the shoreline that is submerged at high tide and exposed to air at low tide. invertebrate: animal without a backbone. involuntary muscle: a muscle that can’t be consciously controlled, such as heart and digestive muscle. islets of Langerhans: cells in the pancreas that produce insulin. J kingdom: the highest and largest of the taxonomic categories; kingdoms include all other categories. L larva: young organism that develops between egg and adult stages. larynx: airway to which the vocal cords are attached; the structure between the pharynx and trachea. lichen: an organism made up of a fungus and green algae living in a mutualistic relationship. life span: the length of time an organism is expected to live. ligament: a tough band of tissue that holds bones together at joints. limiting factor: any biotic or abiotic factor that restricts the number of individuals in a population. lymph: fluid in body tissues made up of water, dissolved substances, and lymphocytes. lymph nodes: bean-shaped structures throughout the body that filter microorganisms and foreign material from lymph before it returns to blood. lymphatic system: collects fluid from body tissues and returns it to the blood. lymphocyte: a type of white blood cell that fights disease-causing antigens by engulfing and digesting them. joint: any place where two or more bones meet; may be movable or immovable. lysosome: a cytoplasmic organelle that contains chemicals and digests wastes and worn-out cell parts. K M kidney: the major organ of the urinary system; filters blood to produce waste liquid called urine. mammal: a endothermic vertebrate with insulating hair and mammary glands. mammary glands: glands in female mammals that produce mild for feeding young. multiple alleles: having more than two alleles that control a trait. mantle: in a mollusk, the thin layer of tissue that covers the soft body; it secretes chemicals that become a shell or protects the body if no shell exists. muscle: an organ that can relax and contract to allow movement. marsupial: a mammal with a pouch on its abdomen for carrying and nursing its young. mechanical digestion: physical breakdown of food into smaller particles by chewing (in the mouth) and by churning (in the stomach). medusa: a bell-shaped cnidarians that is free swimming. meiosis: the division of the cell nucleus to produce sex cells. metabolism: all of the chemical activities of an organism that enable it to live, grow, and reproduce. mutation: any permanent change in an organism’s genetic material (DNA). mutualism: a symbiotic relationship that benefits both partners. N natural resources: parts of the environment that organisms need for survival, such as air, water, soil, and food. natural selection: Darwin’s theory of evolution, which says that organisms best adapted to their environment are more likely to survive and pass their traits to their offspring. nephron: the tiny filtering unit of the kidney. metamorphosis: the changes in body form during the life cycle. nerves: takes in information and sends it throughout the body. mitochondria: cell organelles that break down food molecules and release energy. nervous system: controls the body’s response to information. mitosis: the process by which a nucleus divides into two identical cells, each containing the same number and type of chromosomes as the parent cell. neuron: nerve cell that carries impulses throughout the body; the basic unit of the nervous system. mollusk: a soft-bodied invertebrate that usually has a hard shell. molting: the periodic shedding and replacing of the old, outgrown body covering, such as skin or an exoskeleton. monotreme: a mammal that lays eggs having a tough leathery shell. motor neuron: nerve cell that conducts impulses from the brain or spinal cord to muscles or glands throughout the body. niche: the role of an organism in the ecosystem. noncommunicable disease: a disease that cannot be spread from one organism to another; may be caused by genetics, chemicals, poor diet, or uncontrolled cell division. nonrenewable resource: a natural resource that is available only in limited amounts and that cannot be replaced by nature in a short period of time. nonvascular plant: a plant lacking vascular tissue; it absorbs water directly through its cell membranes. notochord: a flexible, rodlike structure along the dorsal side of a chordate animal; the backbone in vertebrates. nuclear energy: energy produced from the splitting apart of uranium nuclei by a nuclear fission reaction. nucleus: the structure inside a cell that directs the cell’s activities; contains chromatin; chromosomes in a dividing cell. nutrient: a substance in food that produces energy and materials for life activities. O observation: to describe something using one of your senses. omnivore: an animal that eats both plants and animals. open circulatory system: a type of blood-circulation system that lacks vessels but instead bathes internal organs in blood, such as in mollusks. order: the fourth-highest taxonomic category, below a class. organ: a structure made up of different types of tissues that work together to do a specific job; for example the heart. organelles: in eukaryotic cells, the structures within the cytoplasm that break down food, moves wastes, and store materials. organism: a living thing that is made of one or more cells, uses energy, moves, responds to its environment, adjusts, reproduces, adapts, and has a life span. organ system: a group of organs working together. osmosis: the diffusion of water through a cell membrane. ozone depletion: the thinning of Earth’s ozone layer. P parasitism: a symbiotic relationship that benefits the parasite but harms the parasite’s partner. passive transport: movement of material across a cell membrane without the use of energy. pasteurization: heating food long enough to kill most bacteria. pathogen: any organism that produces a disease. pedigree: a diagram that shows the occurrence of a trait in a family. peripheral nervous system: part of the control system, including cranial nerves and spinal nerves that connect the brain and spinal cord to other body parts. peristalsis: muscular contractions that move food through the digestive system. pesticide: a chemical that kills undesirable plants or animal pests. pharynx: a tubelike passageway for both food and air, located between the nasal cavity and the esophagus. phenotype: a physical trait that shows as a result of an organism’s particular genotype. phloem: vascular plant tissue made up of tubular cells that move food from leaves and stems to other parts of the plant for use or storage. photosynthesis: chemical reaction used by producers, such as green plants, to produce food; light energy is used to produce chemical energy, converting carbon dioxide and water into sugar and oxygen. phylogeny: the evolutionary history of an organism. phylum: the second-highest taxonomic category in the animal kingdom. pioneer community: the first community to inhabit a new environment. pioneer species: the first plants to grow in a new or disturbed area. pistil: the female reproductive organ of a flower. placebo: a control that simulates a medicine but doesn’t have the active ingredient. plankton: microscopic algae, plants, and other organisms that float in lakes, ponds, oceans, and other bodies of water. plasma: the liquid part of blood, made mostly of water but also containing dissolved nutrients, minerals, and oxygen. pollen grain: the male reproductive part of a plant that contains the sperm. pollination: the process that transfers pollen grains from the stamen to the stigmas. pollutant: any substance that contaminates the environment; mostly made up of waste products from burning fossil fuels. polygenic inheritance: occurs when groups of gene pairs act together to produce a specific trait. polyp: a vase-shaped cnidarians that usually is sessile. population: organisms of one species that live in the same place at the same time and that can produce offspring. primary succession: the development of new communities in areas that do not have any soil. producers: green plants that make their own food by photosynthesis. protein: a nutrient made up of amino acids; used throughout the body for growth and to replace and repair cells. protists: members of the Kingdom Protista; some are plantlike, others are animal-like, and others are fungus-like; simple one cells or many celled organisms. protozoa: one cells animal like protists; many are parasites. pseudopod: a footlike cytoplasmic extension used by some organisms to move and to trap food. pulmonary circulation: the path of blood from the heart, to the lungs, and back to the heart. pulse: the number of contractions of the heart in a specific time. punctuated equilibrium: a model of evolution, showing the rapid change of a species caused by the mutation of just a few genes. Punnett square: a tool that shows how genes can combine; used to predict the probability of types of offspring. Q population density: the number of individuals per unit of living space. qualitative: describing the general characteristics of something. precipitation: the amount of moisture that condenses and falls as rain, sleet, hair, or snow, or that forms as fog. quantitative: describing something using exact measurements. predation: the feeding of one organism on another organism. preening: a behavior of birds in which a bird uses its beak to rub oil over its feathers to condition them and help make them water repellant. R radial symmetry: describes animals with body parts arranged in a circle around a central point, similar to a bicycle wheel. radula: in gastropods, a tongue-like organ with tows of teeth that scrape and tear food. saprophyte: any organism that uses dead material as a food and energy source. recessive: the form of a trait that seems to disappear in a population but can reappear depending on the way the alleles combine. scales: hard, thin, overlapping plates that cover and protect a fish’s body. recycling: the reusing of an item or resource after it has been changed or reprocessed. red tide: an algal population explosion that causes the water to look red and can cause fish kills and illness. regeneration: the ability of an organism to replace body parts; a type of asexual reproduction in which a whole new organism grows from just a part of the parent organism. relative dating: estimating the age of a fossil by comparing it to younger fossils in the rock layers above and to older fossils in the rock layers below. renewable resource: a natural resource that is constantly being recycled or replaced by nature. reptile: an ectothermic vertebrate that has dry, scaly skin and that lays eggs covered with a leathery shell. respiration: the process by which organism break down food to release energy. response: the reaction of an organism to a stimulus. ribosome: a cell organelle on which protein is made. RNA: ribonucleic acid; carries codes for making proteins. S saliva: the watery substance produced in the mouth that begins the chemical digestion of food. sample size: the amount of people or thing being tested. scientific methods: problem solving procedures used by scientists; define the problem, make a hypothesis, test the hypothesis, analyte the results, and draw conclusion. secondary succession: a type of ecological succession that occurs in a place that has soil and was once the home of living organisms. sensory neuron: nerve cell that transmits stimuli from receptors to the brain or spinal cord. sessile: describes organisms, such as trees, that remain attached to one place during their lifetime. setae: in a segmented worm, bristle-like structures on the outside of the body that help it grip soil and move. sex-linked gene: an allele inherited on a sex chromosome. sexual reproduction: a type of reproduction in which a new organism is produced by combining sex cells from two parents. simulation: an experience that is meant to mimic, or be like, another experiment. skeletal muscles: voluntary muscles that work in pairs and move bones. skeletal system: the body’s network of bones, which forma rigid frame to support the body, protect internal organs, generate red blood cells, and store calcium and phosphorus. smog: a brown colored air pollution that occurs when sunlight reacts with waste products released by the burning of fuels. smooth muscles: involuntary muscles that move many internal organs. soil depletion: the removal of soil nutrients due to the taking away of mature plants form where they were grown. taxonomy: the science of classifying and naming organisms. soil management: the use of plowing methods to prevent soil depletion and erosion. temperate deciduous forest: climax communities of deciduous trees, which lose their leaves in the fall. solid wastes: unwanted, solid materials that can be recycled, burned, buried, or dumped. tendon: a thick band of tissue that attaches a muscle to a bone. species: a group of organism whose members successfully reproduce among themselves. tentacles: the armlike structures that surround the mouths of some organisms and help them to capture food. species diversity: the great variety of plants, animals, and other organisms on Earth. spontaneous generation: the theory that nonliving things produce living things. spore: a reproductive cell that forms new organism without fertilization. sporophyte: the spore forming stage of a plant’s life cycle. stamen: the male reproductive organ of a flower. stimulus: anything an organism responds to, such as sound, light, heat, vibration, odor, movement, hunger, thirst, and so on. stomata: small pores in the surface of a plant leaf that allow carbon dioxide, water, and oxygen to enter and leave. symbiosis: a close relationship between two organisms that live together. synapse: the small gap between two neurons across which impulses can travel. systematic circulation: the flow of blood from the heart to all the body tissues (except lungs and heart) and back to the heart. territory: an area that an animal defends from other members of the same species. tissues: groups of similar cells that do the same sort of work. touch receptors: nerve endings that detect pressure in your skin. toxin: a poison produced by disease causing organisms. trachea: a cartilage reinforced tube that carries air to the bronchi. trade-off: something given up in selecting one alternative over another. transgenic crop: a crop of plants that has new DNA inserted into it to improve yield, disease resistance, and so on. transpiration: in plants, loss of water vapor through the stomata of a leaf. tropical rain forest: hot, humid, equatorial biome: it contains the largest number of species. tropism: the response of a plant to a stimulus. T tube feet: in echinoderms, the structures connected to the water-vascular system that help them move and feed. taiga: a cold biome below the tundra; it has coniferous forests and is warmer and wetter than the tundra. tumor: an abnormal growth of tissue. tundra: a very cold, dry, treeless biome where the sun is barely visible during the six to nine months of winter. U urethra: a tube that carries urine from the bladder to the outside of the body. urinary system: a system of excretory organs that tides blood of wastes, excess water, and excess salts. coat; it infects host cells in order to reproduce. voluntary muscle: a muscle you can control, such as arm and leg muscles. W water cycle: the continuous movement of water in the biosphere through evaporation, condensation, and precipitation. urine: waste liquid collected by the kidneys; contains water, salts, and other wastes. water-vascular system: in echinoderms, the network of water filled canals to which thousands of tube feet are connected. V Z vaccination: administration of a weakened virus to develop immunity against a disease. zygote: in organisms that reproduce sexually, the cell that forms in fertilization. vaccine: a solution made from damaged virus or bacteria particles or from killed or weakened viruses or bacteria; can prevent, but not cure, many viral and bacterial diseases. valve: helps blood flow in one direction. variable: in an experiment, the factor tested. variation: the occurrence of an inherited trait that makes an individual different from other members of the same species. vascular plant: a plant containing vascular tissue made up of tube-like cells that transport food and water through the plant. vein: a vessel with one-way valves that moves blood toward the heart, carrying wastes. ventricles: the two lower chambers of the human heart. vertebrate: animal with a backbone. villi: tiny, fingerlike projections on the inner surface of the small intestine. virus: a microscopic particle made of either a DNA or an RNA core and covered with a protein