Title: OCR Document
Author: Readiris
Last saved by: Sandoz
Company: I.R.I.S.

Life Science Glossary
A
•	abiotic (ay bi AHT ihk) 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 immunity: long-lasting immunity caused by the body making its own antibodies in response to an antigen.
•	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.
•	adolescence: the stage of human development that begins around ages 12 to 14 and lasts until age 20. 
•	adulthood: the stage of human development that begins with the end of adolescence and extends into old age. 
•	aerobe: organism that must have oxygen to survive.
•	aggression: a forceful act used to dominate or control another animal. 
•	AIDS: acquired immune deficiency syndrome, a fatal communicable disease caused by the HIV virus; destroys the body's ability to combat disease; spread by sexual contact, by use of contaminated needles, through the placenta, or by nursing from an AIDS-infected mother.
•	algae: plantlike protists that contain chlorophyll and make their own food; they have no roots, stems, or leaves and live in or near water.
•	allele: a different form a gene may have for a trait.
•	allergen: a substance that causes an allergic response in the body. 
•	allergy: an overly strong reaction of the immune system to a foreign substance. 
•	alternation of generations: in some protists and in plants, a continuous cycle that alternates between sporophyte and gametophyte generations.  
•	alveoli (al VE uh li): in the lungs, clusters of tiny, thin walled air sacs at the end of each bronchiole, where oxygen and carbon dioxide are exchanged. 
•	Alzheimer's disease: a disease of unknown cause in which nerve cells in the brain fail to communicate with each other, causing memory loss. 
•	amino (uh MEE noh) 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 partof its life in water and part on land; examples are frogs, toads, and salamanders. 
•	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. 
•	antibody: a protein made by the body in response to a specific antigen. 
•	antigens: proteins and chemicals that are foreign to the body. 
•	antioxidant: a substance that prevents chemicals that enter the body from reacting with oxygen; may stop or prevent cancer. 
•	antiseptic: a substance that kills pathogens on living tissue and helps prevent their re-growth.
•	anus: an opening at the end of the digestive tract through which solid wastes leave the body. 
•	appendage: a structure growing from the body, such as an arm or leg. 
•	artery: elastic-walled vessel that moves blood away from the heart. 
•	Arthropoda (AR thruh pahd uh): 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.
•	asthma: a respiratory disorder in which the bronchial tubes contract rapidly, resulting in shortness of breath or coughing; caused by smoking, allergy" or stress. (Chap. 24, p. 661)
•	atherosclerosis (ath uh roh skluh ROH sus): a circulatory system disorder in which fatty deposits form on artery walls and restrict blood flow.
•	atria (AY tree uh): the two upper 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. 
•	binomial nomenclature: the two-word naming system that provides every organism with its own scientific name.
•	biogas: a mixture of gases that can be burned directly or converted to gas or liquid fuels.  
•	biogenesis: the theory that living things come only from other living things. 
•	biological indicator: species whose health reflects the health of its ecosystem 
•	biomass: organic material from plants or animals that is used for energy 
•	biomaterial: an artificial material that can be used to repair or replace body parts.  
•	biomes (BI ohmz): 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 (bi AHT ihk) factors: living organisms in the environment, such as plants and animals.
•	bladder: the bag-shaped, elastic, muscular organ that stores urine until it leaves the body; can hold up to 500 mL of urine.
•	blood pressure: the force exerted by blood on the walls of the vessels; pressure is highest in the artery ies and in young adults is normally 120 over 80. 
•	bog: low-lying, spongy, wet ground composed 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
•	cambium (KAM bee um): vascular plant tissue that produces new xylem and phloem cells. 
•	cancer: a major chronic disease resulting from uncontrolled cell growth.
•	capillary: a microscopic blood vessel that connects arteries and veins; nutrients, oxygen, and wastes are exchanged through their one-cell-thick walls.
•	captive breeding: the breeding of an endangered species in captivity. 
•	carbohydrate: a nutrient that provides most 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.\
•	cellular respiration: the process by which organisms break down food to release energy. 
•	cellulose: the organic compound that forms plant cell walls; made up of long chains of sugar molecules. 
•	centenarian: a person 100 years of age or older.
•	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.
•	childhood: the stage of human development from infancy to age 12 years. 
•	chlorophyll: the green pigment nessasary for photosynthesis. 

•	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 bronchitis: a respiratory. disease in which too much mucus is produced in the bronchial tubes. 
•	chronic disease: a noncommunicable disease, such as diabetes or cancer, that lasts a long time.
•	chyme (KIME): the thin, watery liquid in the digestive tract; partially digested food.
•	cilia: short, hairlike structures that extend from the cell membrane and help tiny organisms move; found in respiratory passages. 
•	circadian rhythm: behavior that recurs on a 24-hour cycle. 
•	class: third-highest taxonomic category, below phylum (animals) or division (plants). 
•	classify: to group ideas, information, orA5bjects, 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. 
•	closed circulatory system: a type of blood-circulation system in which vessels transport blood to the internal organs, as in humans. 
•	cnidarian (ni DAIR ee uhn): a phylum of hollow-bodied animals with stinging cells.   
•	cochlea (KOH klee uh): a sound-sensitive, fluid-filled structure in the inner ear; shaped like a snail's Shell. 
•	collar cells: in sponges, the lining cells that help water move through the sponge by the beating of flagella.
•	commensalism: a symbiotic relationship that benefits one partner but not the other. 
•	communicable disease: a disease that is transmitted from one organism to another by such agents as 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.
•	conditioning: occurs when a response previously associated with one stimulus becomes associated with another stimulus.
•	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.
•	courtship behaviors: behaviors that help males and females of a species to recognize each other and prepare for mating. 
•	crop: in an earthworm, a sac in the digestive system that stores soil eaten by the worm. 
•	cuticle: a waxy protective layer on the stems and leaves of land plants that helps the plant conserve water.
•	cyclic behavior: innate behavior that occurs in a repeating pattern. 
•	cyst: a young, parasitic worm with a protective covering. 
•	cytoplasm: the gel-like substance inside the cell membrane that contains structures that carry out life processes. 
D
•	day-neutral plant: a plant that isn't very sensitive to the number of hours of darkness and thus can flower over a wide range of night lengths. 
•	dendrite: neuron structure that rec_ves messages and sends them to the cell body. 
•	dermis: the inner layer of skin; it contains many blood vessels, nerves, and sweat and oil glands.
•	desert: the driest biome on Earth; supports little plant life and receives less than 25 cm of rain yearly.
•	development: all the changes undergone by living things as they grow. 
•	diaphragm (DI uh fram): a muscle beneath the lungs, that helps move air in and out of the body.
•	dichotomous (DI kaht uh mus) key: a detailed list of traits used to identify a specific organism. 
•	dicot (DI kaht): an angiosperm having two seed "leaves inside its seed; for example, a maple tree.
•	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. 
•	Diploid: a complete set of chromosomes in a body cell.
•	disinfectant: a substance that kills pathogens on non living objects. 
•	division: second-highest taxonomic category in the plant and fungi kingdoms (in the animal kingdom, phylum replaces division). 
•	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 (ih KI nOO durm): a spiny-skinned invertebrate that lives on the bottom of the ocean and that moves by means of a water-vascular system. 
•	ecological pyramid: a model used to describe the transfer of energy through a community. 
•	ecological succession: the process of gradual change from one community of organisms to another. 
•	ecology: the study of relationships between organisms and between organisms and their physical environments.
•	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 stages of an organism's development.  
•	emphysema (em fOO SEE moo): a respiratory disease in which the alveoli in the lungs lose their ability to expand and contract (elasticity), mostly caused by 	smoking. 
•	endangered species: a species with so few individuals left that it is in danger of extinction. 
•	endocytosis: a process by which cells transport a large body, such as a large protein molecule, through a cell membrane into the cytoplasm. 
•	  endoplasmic reticulum (ER): a cell organelle consisting of folded membranes that move materials around within the cell. 
•	  endoskeleton: the internal skeleton of ,1m organism that supports and protects the internal organs and provides a frame for muscle. 
•	endospore (EN doh spor): a thick-walled structure that some bacteria produce around themselves, p " especially for protection from heat and drought.
•	endotherm: vertebrate animal that maintains a constant body temperature. 
•	enzyme (EN zim): a protein that speeds chemical reactions in cells without being changed itself. 
•	  epidermis: the surface or outer layer of your skin.
•	equilibrium: condition in which molecules of a 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; examples are salt marshes, deltas, and mud flats. 
•	ethnobotanist: a person who studies\ relationships between people from various cultures and theirplants. 
•	evolution: changes that occur over time in the hereditary features of a species of organisms. 
•	exocytosis: a process by which a cell moves large molecules out through the cell membrane. 
•	exoskeleton: on all arthropods, the hard, lightweight
•	  external covering that shields, supports, and protects the body. 
•	extinction: the dying out of an entire species. 
F
•	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.
•	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 CO2,  
•	fertilization: in organisms that reproduce sexually, the fusion of an egg and a sperm (gametes).  
•	fetus (FEE tus): a developing embryo; in humans, the unborn baby after the first two months of pregnancy 
•	filter feeder: an organism that obtains food and oxygen by filtering it from the water in which it lives.  
•	fin: fanlike structure on most fish; adapted for steering, balancing, and moving through the water.  
•	  fish: an 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.
•	flagellum (Huh JELL uhm): a whip-like tail on bacteria and some protists that helps them move through a moist environment.  
•	food chain: a model used to show how energy from food passes from one organism to another. 
•	  food group: a group of foods containing the same nutrients; for example, the bread and cereal group.
•	food web: a model used to describe a series of overlapping food chains. 
•	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.
•	fracture: a break in a bone. 
•	free-living: describes an organism that finds its <own food and place to live without depending on another organism; the opposite of a parasite. 
•	frond: the leaf of a fern. 

G
•	gametophyte: the sex cell-producing stage of a plant's life cycle. 
•	gasohol: a mixture of gasoline and ethanol. 
•	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: paired openings in the throat; in fish, they develop into gills for breathing underwater.
•	gizzard: in an earthworm, a muscular digestive structure that grinds soil. 
•	global warming: the potential warming of Earth due to an increase in greenhouse gases in the atmosphere. 
•	golgi (GAWL jee) bodies: cell organelles consisting of stacks of membrane-covered sacs that package and move proteins to the outside of the cell. 
•	gradualism: a model of evolution, showing a steady,
•	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.

H
•	habitat: the physical location where an organism lives. 
•	Haploid: half the chromosomes of a normal body cell.
•	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. 
•	herbivore: an animal that eats only plants. (Chap. 16,
•	heredity: passing of traits from parent to offspring.
•	hermaphrodite: an animal that produces both sperm and eggs. 
•	heterozygous (het uh roh ZI gus): an organism that has. two different alleles for a trait.
•	hibernation: an adaptation for winter survival during which an animal becomes inactive and all body processes slow down. 
•	homeostasis: the regulation of steady, life-maintaining conditions inside an organism or cell, despite changes m its environment. 
•	hominids: earliest humanlike primates; ate both meat and vegetables and walked upright on two feet.
•	Homo sapiens: our own species, a hominid primate mammal; evolved 300 000 years ago. 
•	homologous: body parts in different species that are similar in origin and structure. 
•	homozygous (ho muh ZI gus): 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.
•	hypertension (hi pur TEN chun): a circulatory system disorder in which blood pressure is too high.
•	hyphae (HI fee): the mass of many-celled, threadlike tubes that form the body of a fungus.)
•	  hypothesis: a prediction that can be tested.
I
•	immovable joint: a juncture of two or more bones made so that little or no movement 
•	immune system: a complex group of defenses that the body uses to fight disease. 
•	imprinting: a type of learned behavior in which an animal forms a social attachment to another organism soon after birth or hatching. 
•	incomplete dominance: the production of a phenotype in an offspring that is intermediate to the phenotypes of its two homozygous parents. 
•	incubate: to keep an egg or newborn animal warm; the heat helps eggs develop until they hatch and helps young to survive. 
•	infancy: the stage of human development from four weeks after birth to one year. 
•	innate behavior: behavior that an organism is born with and does not have to learn. 
•	inorganic compound: class of compounds made from elements other than carbon-for example, water.
•	insight: a form of reasoning to use past experiences that enables animals to solve new problems.
•	instinct: a complex pattern of innate behavior involving multiple actions. 
•	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 a 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
•	  joint: any place where two or more bones meet; may be movable or immovable. 
K
•	kidney: the major organ of the urinary system; filters blood to produce the waste liquid called urine. 
•	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.
•	law: a rule that describes a pattern in nature and what will happen under specific conditions. 
•	learning: the process of developing a behavior through experience or practice. 
•	lichen: an organism made up of a fungus and green  algae or a cyanobacterium 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. 
•	long-day plant: a plant that requires short nights (long days) to flower. 
•	lymph (LIHMF): 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 (lihm FAT ihk) system: collects fluid from body tissues and returns it to the blood through lymphatic capillaries and lymph vessels.
•	lymphocyte (LIHM fuh site): a type of white blood cell that fights disease-causing antigens by engulfing and digesting them.
•	lysosome (LI suh sohm): a cytoplasmic organelle that contains chemicals and digests wastes and worn- r-. out cell parts. 
M
•	mammal: an endothermic vertebrate with insulating hair and mammary glands.
•	mammary glands: glands in female mammals that produce milk for feeding young. 
•	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. 
•	marrow: a red or, yellow fatty tissue in certain bones that produces red and white blood cells. 
•	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 cnidarian that is free swimming. 
•	meiosis: the division of the cell nucleus to produce sex cells (gametes). 
•	melanin (MEL uh nun): a pigment produced by the epidermis that gives skin its color.
menopause: in older females,' the period of years - when the menstrual cycle becomes irregular and  eventually stops. 
•	menstrual (MEN strul) cycle: in females, the hormonally regulated cycle of egg production and men struation. 
•	menstruation (men STRAY shun): in females, the monthly shedding of the lining of the uterus that takes place if fertilization of an egg has not occurred.
•	metabolism: all of the chemical activities of an organism that enable it to live, grow, and reproduce.
•	metamorphosis: the changes in body form during the life cycle-for example: egg, larva, pupa, adult. 
•	migration: the instinctive seasonal movement of animals, such as birds flying south for the winter. 	.
•	minerals: inorganic nutrients that regulate many chemical reactions in the body, such as building cells and sending nerve impulses. 
•	mitochondria: cell organelles that break down food
•	molecules and release energy. 
•	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. 
•	mixture: a combination of two or more substances in which individual substances retain their own properties. 
•	mollusk: a soft-bodied invertebrate that usually has a hard shell, such as a snail. 
•	molting: the periodic shedding and replacing of the old, outgrown body covering, such as skin or an exoskeleton. 
•	monocot (MAHN uh kaht): an angiosperm having a single seed leaf inside its seed; for example, an orchid.
•	monotreme: a mammal that lays eggs having tough, leathery shells; for example, the duckbilled platypus. 
•	motivation: some stimulus within an animal that causes it to act. 
•	motor neuron: nerve cell that conducts impulses from the brain or spinal cord to muscles or glands throughout the body. 
•	movable joint: a place where two or more bones meet or are attached and allow a wide range of movement. 
•	multiple alleles: having more than two alleles that control a trait. 
•	muscle: an organ that can relax and contract to allow movement. 
•	mutation: any permanent change in an organism's genetic material (DNA). 
•	mutualism: a symbiotic relationship that benefits both partners.    
•	 mycorrhiza: the symbiotic association of the mycelium of a fungus with the roots of a seed plant
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 arid pass their traits to their offspring. 
•	nephron (NEF rahn): the tiny filtering in the kidney. 
•	neuron: nerve cell that carries impulses throughout the body; the basic unit of the nervous system.
•	niche: the role of an organism in the- ecosystem.
•	nitrogen cycle: the continuous movement of nitrogen from -the atmosphere, to plants, and back to the
•	atmosphere (or directly into plants) again. 
•	nitrogen-fixing bacteria: bacteria that change nitrogen from the air into nitrogen compounds that are useful to plants and animals. 
•	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, rod like structure along the dorsal side (back) of a chordate animal; the backbone in vertebrates.	I
•	nuclear energy: energy produced from the splitting  apart of uranium nuclei by ‘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
•	olfactory cell: nerve cells in the nasal passages that respond to chemical stimuli in air. 
•	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, move wastes, and store materials.
•	organic compound: class of compounds in living organisms: carbohydrates, lipids, proteins, and nucleic acids.
•	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. 
•	osmosis: the diffusion of water through a cell membrane. 
•	osteoporosis: a disease that breaks down bone, making it brittle and weak. 
•	ovary: in angiosperms, the swollen base of the pistil, where ovules form; in female animals, the organ that produces ova, or egg cells. 
•	ovulation (ahv yuh LAY shun): in human females, the monthly process of egg release from an ovary.
•	ovule (OHV yewl): the female reproductive part of a plant that produces the eggs. 
•	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 immunity: short-term immunity caused by antibodies introduced into the body from an outside source. 
•	passive smoking: the breathing in of cigarette smoke filled air by nonsmokers. 
•	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 disease.
•	pedigree: a diagram that shows the occurrence of a trait in a family. 
•	  periosteum (per ee AHS tee um): a tough, tight-fitting membrane that covers the surface of bones. 
•	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 (pe ruh STAHL sis): muscular contractions that move food through the digestive system. 
•	permafrost: in tundra areas of Earth, the nutrientpoor soil that remains permanently frozen underneath the top few inches of soil. 
•	pesticide: a chemical that kills undesirable plants or animal pests. 
•	pharynx (FER ingks): a tube-like passageway for both food and air, located between the nasal cavity and the esophagus. 
•	phenotype (FEE nuh tipe): a physical trait that shows as a result of an organism's particular genotype.
•	  pheromone: a powerful chemical produced by an animal to influence the behavior of another animal of the same species.
•	phloem (FLOH em): 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. 
•	photoperiodism: the flowering response of a plant to changes in the length of day and night. 
•	photosynthesis (foht oh SIHN thuh sus): 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. 
•	photovoltaic (PV) cell: a solar cell that turns sunlight directly into electric current. 
•	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; their decay creates material in which other plant species grow. 
•	pistil (PIHS tul): the female reproductive organ of a flower. 
•	placenta: in placental mammals, the saclike organ developed by a growing embryo; attaches to the uterus; absorbs food and oxygen from the mother's blood. 
•	placental mammal: a mammal whose young develop inside the female in the uterus. 

•	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. 
•	platelet: an irregularly shaped cell fragment that helps blood clot. 
•	pollen grain (PAHL un GRAYN): 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 (pahl ih JENH ink) inheritance: occurs when groups of gene pairs act together to produce a specific trait. 
•	polyp: a vase-shaped cnidarian that usually is sessile.
•	population: organisms of one species that live in the same place at the same time and that can produce offspring. 
•	population density: the number of individuals per unit of living space. 
•	precipitation: the amount of moisture that condenses and falls as rain, sleet, hail, or snow, or that forms as fog. 
•	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 repellent. 
•	pregnancy: the period of time between fertilization and birth (in humans, nine months). 
•	primary succession: the development of new communities in areas that do not have any soil, such as new volcanic islands. 
•	primates: the group of mammals to which monkeys, apes, and humans belong and which share several characteristics, such as opposable thumbs. 
•	producers: an organism, such' as green plants, that makes its own food by photosynthesis. 
•	protein: a nutrient made up of amino acids; used throughout the body for growth and to replace and repair cells. 
•	 prothallus: the structure in ferns that produces gametes. 
•	protists: members of the Kingdom Protista; some are plantlike, others are animal-like, and others funguslike; simple one-celled or many-celled organisms. 
•	Protozoa (proht uh ZOH uh): one-celled animal-like protists; many are parasites.  
•	pseudopod (SEWD uh pahd): a footlike cytoplasmic extension used by some organisms to move and to trap food. 
•	pulmonary (PUL mo ner e) circulation: the path of blood from the heart, to the lungs, and back to the heart. 
•	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 and  used to predict the probability of types of offspring. 
R
•	radial symmetry: describes animals with body parts arranged in a circle around a central point, similar to a bicycle wheel. 
•	radioactive element: an element that gives off radiation, a form of atomic energy.
•	radula: in gastropods, a tongue-like organ with rows of teeth that scrape and tear food. 
•	recessive: the form of a trait that seems to disappear in a population but can reappear depending on the way the alleles combine. 
•	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.
•	reflex: the simplest type of innate behavior; an automatic, involuntary response to a stimulus. 
•	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; examples are lizards, snakes, and turtles. 
•	respiration: the process by which organisms break down food to release energy. 
•	response: the reaction of an organism to a stimulus.
•	retina: light-sensitive tissue at the back of the eye.
•	rhizoid: root like filament containing only a few long cells; it holds moss plants in place. 
•	rhizome: the underground stem of a fern. 
•	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. 
•	saprophyte (SA proh fite): any organism that uses dead material as a food and energy source. 
•	  scales: hard, thin, overlapping plates that cover and protect a fish's body. 
•	scientific methods: problem-solving procedures used by scientists; define the problem, make a hypothesis, test the hypothesis, analyze the results, and draw conclusions. 
•	sea otter: a carnivorous placental mammal with a well-developed brain and good under water vision. 
•	secondary succession: a type of ecological succession that occurs in a place that has soil and was once the home of living organisms. 
•	sedimentary rock: a type of rock formed when fine particles like mud and sand settle out of water and become cemented together. 
•	semen: the mixture of sperm and a fluid that nourishes the sperm and helps them move. 
•	  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 th_ir lifetime.
•	setae (SEE tee): 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.)
•	sexually transmitted disease (STD): a disease transmitted from person to person during sexual contact.	_
•	short-day plant: a plant that requires long nights (short days) to flower. 
•	skeletal muscles: voluntary muscles that work in pairs and move bones.;.. )
•	skeletal system: the body's network of bones, which form a 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, such as the stomach, intestines, and blood vessels.
•	social behavior: interactions between organisms of the same species, including mating, caring for young, getting food, and claiming territory.
•	society: a group of animals of the same species living and working together in an organized way. 
•	soil depletion: the removal of soil nutrients due to the taking away of mature plants from 'Where they were grown. 
•	soil management: the use of plowing methods to prevent soil depletion and erosion. 
•	solid wastes: unwanted, solid materials that must be disposed of; it can be recycled, burned, buried, or dumped. 
•	sorus: structure that produces spores on the under side of a fern frond. 
•	species: a group of organisms whose members successfully reproduce among themselves. 
•	species diversity: the great variety of plants, animals, and other organisms on Earth. 
•	sperm: the gamete or reproductive cell from the male parent produced in the testes. 
•	spiracles: in an arthropod, openings in the abdomen and thorax through which air enters and waste gases leave. 
•	spontaneous generation: the theory that nonliving things produce living things; for example, that frogs arise spontaneously from mud. 
•	sporangia: the round spore cases of zygote fungi.
•	spore: a reproductive cell that forms new organisms without fertilization; in fungi, ferns, and some protists. 
•	sporophyte: the spore-forming stage of a plant's life cycle. 
•	stamen (STAY mun): 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. 
•	systemic (sihs TEM ihk) circulation: the flow of blood from the heart to all the body tissues (except lungs and heart) and back to the heart. 
T
•	taiga: a cold biome south of the tundra; it has coniferous forests and is warmer and wetter than the tundra. 
•	target tissue: specific tissue affected by hormones.
•	taste buds: the major taste receptor tissue located on the tongue that responds to chemical stimuli.
•	  taxonomy (tak SAHN uh mee): the science of classifying and naming organisms. 
•	technology: the use of scientific knowledge to improve the quality of human life or to solve problems.
•	temperate deciduous forest: a biome containing climax communities of deciduous trees, which lose their leaves in the fall. 
•	tendon: a thick band of tissue that attaches a muscle to a bone. 
•	tentacles: the arm like structures that surround the mouths of some organisms and help them to capture food. 
•	territory: an area that an animal defends from other members of the same species. 
•	testis: organ in males that produces sperm and testosterone.
•	theory: an explanation of nature, based on many observations; subject to change when evidence changes. 
•	tissues: groups of similar cells that do the same sort of work; for example, all muscle tissue contracts..
•	toxin: a poison produced by disease-causing organisms (pathogens). 
•	trachea: a cartilage-reinforced tube that carries air to the bronchi. 
•	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. 
•	trial and error: a type of learning in which behavior is modified by experience. 
•	tropical rain forest: hot, humid, equatorial biome; it contains the largest number of species. 
•	tropism: the response of a plant to a stimulus. 
•	tube feet: in echinoderms, the structures connected to the water-vascular system that help them move and feed. 
•	tumor: an abnormal growth of tissue. 
•	tundra (TUN dra): a very cold, dry, treeless biome where the sun is barely visible during the six to nine months of winter. 
U
•	umbilical cord: in placental mammals, a bundle of blood vessels connecting the placenta to the embryo; transports nutrients and oxygen from the placenta to the embryo and carries away wastes. 
•	ureters (YOOR ut urz): tubes that lead from each kidney to the bladder. 
•	urethra (yoo REE thruh): a tube that carries urine from the bladder to the outside of the body. 
•	urinary system: a system of excretory organs that rids blood of wastes, excess water, and excess salts.
•	urine: waste liquid collected by the kidneys; contains water, salts, and other wastes.  
•	uterus: in females, the pear-shaped, hollow, muscular organ in which a fertilized egg develops into a baby; also called the womb.  
V
•	  vaccination: administration of a weakened virus to develop immunity against a disease. 
•	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.  
•	vagina: in females, the passage way that leads from the uterus to outside of the female's body; also called the birth canal because offspring pass through it when being born. 
•	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 tubelike 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 (VEN trih kulz): the two lower chambers of the human heart. 
•	vertebrate: animal with a backbone. 
•	vestigial structure: a body part that is reduced in size and that has no obvious use.  
•	villi (VIHL i): 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 coat; it infects host cells in order to reproduce. 
•	vitamins: organic nutrients that promote growth, regulate body functions, and help the body use other nutrients. 
•	  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. 
•	water-vascular system: in echinoderms, the network of water-filled canals to which thousands of tube feet are connected. 
X
•	xylem (ZI lum): vascular plant tissue made up of tubular vessels that transport water and minerals from the roots up through the plant. 
Z
•	zygote: in organisms that reproduce sexually, the cell that forms in fertilization.