Bihar School Holidays Calendar 2025

From, System, type, Body, Cell, Cells, Such, Blood, Species, Other, Through, process, Into, Plant, Water, Between, Same, Tissue, During, Occurs,

Biology Glossary

Abiotic Factor	Nonliving aspect of the environment such as sunlight and soil
Absolute Dating	Carbon-14 or other method of dating fossils that gives an approximate age in years
Absorption	Process in which substances such as nutrients pass into the blood stream
Acid	Solution with a ph lower than 7
Acid Rain	Low-ph precipitation that forms with air pollution combines with water
Acquired Immunodeficiency Syndrome (AIDS)	Disorder characterized by frequent opportunistic infections that eventually develops in people who are infected with human immunodeficiency virus (HIV)
Action Potential	Reversal of electrical charge across the membrane of a resting neuron that travels down the axon of the neuron as a nerve impulse
Activation Energy	Energy needed to start a chemical reaction
Active Immunity	Ability to resist a pathogen that results when an immune response to the pathogen produces memory cells
Active Transport	Movement of substances across a plasma membrane that requires energy
Adaptation	Characteristic that helps living things survive and reproduce in a given environment
Adaptive Radiation	Process by which a single species evolves into many new species to fill available niches
Adolescence	Period of transition between the beginning of puberty and adulthood during which significant physical, mental, emotional, and social changes occur
Adolescent Growth Spurt	Period of rapid growth that occurs during puberty
Adrenal Glands	Pair of endocrine glands located above the kidneys that secrete hormones such as cortisol and adrenaline
Aerobic Respiration	Type of cellular respiration that requires oxygen
Age-Sex Structure	Number of individuals of each sex and age in a population
Aggression	Behavior that is intended to cause harm or pain
Air Pollution	Chemical substances and particles released into the air mainly by human actions such as burning fossil fuels
Air Quality Index (Aqi)	Assessment of the levels of pollutants in the outdoor air that is based on their human health effects
Alcoholic Fermentation	Type of anaerobic respiration that includes glycolysis followed by the conversion of pyruvic acid to ethanol and carbon dioxide and the formation of NAD+
Algae (Singular, Alga)	Plant-like protists such as diatoms and seaweeds
Algal Bloom	Excessive growth of algae in bodies of water because of high levels of nutrients, usually from fertilizer in runoff
Allele	One of two or more different versions of the same gene
Allele Frequency	How often an allele occurs in a gene pool relative to the other alleles for that gene
Allergen	Any antigen that causes an allergy
Allergy	Disease in which the immune system makes an inflammatory response to a harmless antigen
Allopatric Speciation	Evolution of a new species that occurs when some members of an original species become geographically separated from the rest of the species
Alternation Of Generations	Change back and forth from one generation to the next between haploid gametophyte and diploid sporophyte stages in the life cycle of plants
Alveoli (Singular, Alveolus)	Tiny sacs at the ends of bronchioles in the lungs where pulmonary gas exchange takes place
Amoeboid	Type of protozoa, such as Amoeba, that moves with pseudopods
Amino Acid	Small molecule that is a building block of proteins
Amniote	Animal that produces eggs with internal membranes that allow gases but not water to pass through so the embryo can breathe without drying out (reptile, bird, or mammal)
Amniotic Sac	Enclosed membrane containing fluid that surrounds and protects a fetus
Amphibian	Ectothermic, tetrapod vertebrate that may live on land but must return to water in order to reproduce
Anabolic Reaction	Endothermic reaction in organisms
Anaerobic Respiration	Type of cellular respiration that does not require oxygen
Analogous Structure	Structure that is similar in unrelated organisms because it evolved to do the same job, not because it was inherited from a common ancestor
Anaphase	Third phase of mitosis during which sister chromatids separate and move to opposite poles of the cell
Angiosperm	Type of seed plant that produces seeds in the ovary of a flower
Animal	Heterotrophic, multicellular eukaryote with cells that lack cell walls; member of the animal kingdom
Animal Behavior	Any way that animals interact with each other or the environment
Annelida	Invertebrate phylum of segmented worms such as earthworms
Antheridia (Singular, Antheridium)	Male reproductive organs of the gametophyte generation of plants that produce motile sperm
Antibiotic Drug	Drug that kills bacteria and cures bacterial infections and diseases
Antibiotic Resistance	Ability to withstand antibiotic drugs that has evolved in some bacteria
Antibody	Large, Y-shaped proteins produced by B cells that recognize and bind to antigens in a humoral immune response
Antigen	Molecule that the immune system identifies as foreign and responds to by forming antibodies
Aphotic Zone	Area in aquatic biomes deeper than 200 meters
Aquatic Biome	Water-based biomes, defined by the availability of sunlight and the concentration of dissolved oxygen and nutrients in the water
Aquifer	Underground layer of rock that stores water
Arboreal	Of or pertaining to trees, as in arboreal, or tree-living, mammal
Archaea	One of two prokaryote domains that includes organisms that live in extreme environments
Archegonia (Singular, Archegonium)	Female reproductive organs of the gametophyte generation of plants that produce eggs
Artery	Type of blood vessel that carries blood away from the heart toward the lungs or body
Arthropod	Invertebrate in the phylum Arthropoda, characterized by a segmented body, hard exoskeleton, and jointed appendages
Artificial Selection	Process in which organisms evolve traits useful to humans because people select which individuals are allowed to reproduce and pass on their genes to successive generations
Asexual Reproduction	Reproduction that involves a single parent and results in offspring that are all genetically identical to the parent
Asthma	Respiratory system disease in which air passages of the lungs periodically become too narrow, making breathing difficult
Atherosclerosis	Condition in which plaque builds up inside arteries
Athlete’s Foot	Infection of the skin between the toes by the fungus Trichophyton
ATP (Adenosine Triphosphate)	Energy-carrying molecule that cells use to power their metabolic processes
Autoimmune Disease	Type of disease, such as type 1 diabetes, in which the immune system attacks the body’s cells as though they were pathogens
Autonomic Nervous System (ANS)	Division of the peripheral nervous system that controls involuntary activities not under conscious control such as heart rate and digestion
Autosome	Chromosomes 1–22 in humans that contain genes for characteristics unrelated to sex
Autotroph	Organism that makes its own food
Axon	Long extension of the cell body of a neuron that transmits nerve impulses to other cells
Bacteria	Domain of prokaryotes, some of which cause human diseases
Bark	Tissue that provides a rough, woody external covering on the stems of trees
Base	Solution with a ph higher than 7
B Cell	Type of lymphocyte that fights infections by forming antibodies
Bilateral Symmetry	Symmetry of a body plan in which there are distinct head and tail ends, so the body can be divided into two identical right and left halves
Bile	Fluid produced by the liver and stored in the gall bladder that is secreted into the small intestine to help digest lipids and neutralize acid from the stomach
Binary Fission	Type of cell division that occurs in prokaryotic cells in which a parent cells divides into two identical daughter cells
Binomial Nomenclature	Method of naming species with two names, consisting of the genus name and species name
Biochemical Reaction	Chemical reaction that occurs inside the cells of living things
Biodiversity	The variety of life and its processes; including the variety of living organisms, the genetic differences among them, and the communities and ecosystems in which they occur
Biofilm	Colony of prokaryotes that is stuck to a surface such as a rock or a host’s tissue
Biogeochemical Cycle	Interconnected pathways through which water or a chemical element such as carbon is continuously recycled through the biotic and abiotic components of the biosphere
Biogeography	Study of how and why plants and animals live where they do
Biology	Science of life, study of life
Biomass	Total mass of organisms at a trophic level
Biome	Group of similar ecosystems with the same general type of physical environment
Biosphere	Part of Earth where all life exists, including land, water, and air
Biotechnology	Use of technology to change the genetic makeup of living things in order to produce useful products
Bioterrorism	Intentional release or spread of agents of disease
Biotic Factor	Living aspects of the environment, including organisms of the same and different species
Bird	Bipedal, endothermic, tetrapod vertebrate that lays amniotic eggs and has wings and feathers
Bladder	Hollow, sac-like organ that stores urine until it is excreted from the body
Blastocyst	Fluid-filled ball of cells that develops a few days after fertilization in humans
Blood	Fluid connective tissue that circulates throughout the body through blood vessels
Blood Pressure	Force exerted by circulating blood on the walls of blood vessels
Blood Type	Genetic characteristic associated with the presence or absence of antigens on the surface of red blood cells
Body Mass Index (BMI)	Estimate of the fat content of the body calculated by dividing a person’s weight (in kilograms) by the square of the person’s height (in meters)
Bone	Hard tissue in most vertebrates that consists of a collagen matrix, or framework, filled in with minerals such a calcium
Bone Marrow	Soft connective tissue in spongy bone that produces blood cells
Bone Matrix	Rigid framework of bone that consists of tough protein fibers and mineral crystals
Brain	Central nervous system organ inside the skull that is the control center of the nervous system
Brain Stem	Lowest part of the brain that connects the brain with the spinal cord and controls unconscious functions such as heart rate and breathing
Bryophyte	Type of plant that lacks vascular tissues, such as a liverwort, hornwort, or moss
Budding	Type of asexual reproduction in yeasts in which an offspring cell pinches off from the parent cell
Calvin Cycle	Second stage of photosynthesis in which carbon atoms from carbon dioxide are combined, using the energy in ATP and NADPH, to make glucose
Cambrian Explosion	Spectacular burst of new life that occurred at the start of the Paleozoic Era
Cancer	Disease that occurs when the cell cycle is no longer regulated and cells divide out of control
Candidiasis	Infection of the mouth or of the vagina in females that is caused by the yeast Candida
Capillary	Smallest type of blood vessel that connects very small arteries and veins
Capsid	Protein coat that surrounds the DNA or RNA of a virus particle
Carbohydrate	Organic compound such as sugar or starch
Carbon Cycle	Interconnected pathways through which carbon is recycled through the biotic and abiotic components of the biosphere
Carcinogen	Anything that can cause cancer
Cardiac Muscle	Involuntary, striated muscle found only in the walls of the heart
Cardiovascular Disease (CVD)	Any disease that affects the heart or blood vessels
Carnivore	Consumer that eats animals
Carrying Capacity (K)	Largest population size that can be supported in an area without harming the environment
Cartilage	Dense connective tissue that provides a smooth surface for the movement of bones at joints
Catabolic Reaction	Exothermic reaction in organisms
Cell	Basic unit of structure and function of living things
Cell Body	Central part of a neuron that contains the nucleus and other cell organelles
Cell Cycle	Repeating series of events that a cell goes through during its life, including growth, DNA, synthesis, and cell division
Cell Division	Process in which a parent cell divides to form two daughter cells
Cell-Mediated Immune Response	Type of immune response in which T cells destroy cells that are infected with viruses
Cell Theory	Theory that all living things are made up of cells, all life functions occur within cells, and all cells come from already existing cells
Cellular Respiration	Process in which cells break down glucose and make ATP for energy
Cell Wall	Rigid layer that surrounds the plasma membrane of a plant cell and helps support and protect the cell
Cenozoic Era	Age of mammals that lasted from 65 million years ago to the present
Central Dogma Of Molecule Biology	Doctrine that genetic instructions in DNA are copied by RNA, which carries them to a ribosome where they are used to synthesize a protein (DNA → RNA → protein)
Central Nervous System (CNS)	One of two main divisions of the nervous system that includes the brain and spinal cord
Central Vacuole	Large saclike organelle in plant cells that stores substances such as water and helps keep plant tissues rigid
Centromere	Region of sister chromatids where they are joined together
Cephalization	Concentration of nerve tissue in one end of an animal, forming a head region
Cerebellum	Part of the brain below the cerebrum that coordinates body movements
Cerebrum	Largest part of the brain that controls conscious functions such as reasoning and sight
Chargaff’s Rules	Observations by Erwin Chargaff that concentrations of the four nucleotide bases differ among species; and that, within a species, the concentrations of adenine and thymine are always about the same and the concentrations of cytosine and guanine are always about the same
Chemical Bond	Force that holds molecules together
Chemical Digestion	Chemical breakdown of large, complex food molecules into smaller, simpler nutrient molecules that can be absorbed by the blood
Chemical Reaction	Process that changes some chemical substances into others
Chemoautotroph	Producer that uses energy from chemical compounds to make food by chemosynthesis
Chemosynthesis	Process of using the energy in chemical compounds to make food
Chitin	Tough carbohydrate that makes up the cell walls of fungi and the exoskeletons of insects and other arthropods
Chlamydia	Sexually transmitted bacterial infection that is the most common STI in the United States
Chlorophyll	Green pigment in a chloroplast that absorbs sunlight in the light reactions of photosynthesis
Chloroplast	Organelle in the cells of plants and algae where photosynthesis takes place
Chordates	Consists of all animals with a notochord, dorsal hollow nerve cord, post-anal tail, and pharyngeal slits during at least some stage of their life
Chromatid	One of two identical copies of a chromosome that are joined together at a centromere before a cell divides
Chromatin	Grainy material that DNA forms when it is not coiled into chromosomes
Chromosomal Alteration	Mutation that changes chromosome structure
Chromosome	Coiled structure made of DNA and proteins containing sister chromatids that is the form in which the genetic material of a cell goes through cell division
Cilia (Singular, Cilium)	Short, hairlike projections, similar to flagella, that allow some cells to move
Ciliate	Type of protozoa, such as Paramecium, that moves with cilia
Circadian Rhythm	Regular change in biology or behavior that occurs in a 24-hour cycle
Circulatory System	Organ system consisting of the heart, blood vessels, and blood that transports materials around the body
Clade	Group of related organisms that includes an ancestor and all of its descendants
Climate	Average weather in an area over a long period of time
Climax Community	Final stable stage of ecological succession that may be reached in an undisturbed community
Cloaca	Body cavity with a single opening in amphibians, reptiles, and monotreme mammals that collects and excretes wastes from the digestive and excretory systems and gametes from the reproductive system
Cnidaria	Invertebrate phylum that includes animals such as jellyfish and corals that are characterized by radial symmetry, tissues, and a stinger called a nematocyst
Codominance	Relationship between two alleles for the same gene in which both alleles are expressed equally in the phenotype of the heterozygote
Codon	Group of three nitrogen bases in nucleic acids that makes up a code “word” of the genetic code and stands for an amino acid, start, or stop
Coelom	Fluid-filled body cavity
Coevolution	Process in which two interacting species evolve together, with each species influencing the other’s evolution
Commensalism	Symbiotic relationship in which one species benefits while the other species is not affected
Community	All of the populations of different species that live in the same area
Compact Bone	Dense outer layer of bone that is very hard and strong
Comparative Anatomy	Study of the similarities and differences in the structures of different species
Comparative Embryology	Study of the similarities and differences in the embryos of different species
Competition	Relationship between living things that depend on the same resources in the same place and at the same time
Competitive Exclusion Principle	Principle of ecology stating that two different species cannot occupy the same niche in the same place for very long
Complementary Base Pair	Pair of nucleotide bases that bond together—either adenine and thymine (or uracil) or cytosine and guanine
Complete Digestive System	Digestive system consisting of a digestive tract and two body openings (mouth and anus)
Compound	Substance with a unique, fixed composition that consists of two or more elements
Condensation	Process in which water vapor changes to tiny droplets of liquid water
Cone	Structure consisting of scales that bear naked seeds in the type of seed plants called gymnosperms
Connective Tissue	Tissue made up of cells that form the body’s structure, such as bone and cartilage
Consumer	Organism that consumes other organisms for food
Cooperation	Type of animal behavior in which social animals live and work together for the good of the group
Courtship	Animal behavior that is intended to attract a mate
Cranium	Part of a vertebrate endoskeleton that encloses and protects the brain; also called the skull
Crop	Sac-like structure in the digestive system of birds that stores and moistens food before it is digested
Crossing-Over	Exchange of genetic material between homologous chromosomes when they are closely paired during meiosis I
Cuticle	Waxy, waterproof substance produced by epidermal cells of leaves, shoots, and other above-ground parts of plants to prevent damage and loss of water by evaporation
Cyanobacteria	Gram-positive blue-green photosynthetic bacteria of the type that added oxygen to Earth’s early atmosphere and evolved into chloroplasts of eukaryotic cells
Cytokinesis	Splitting of the cytoplasm to form daughter cells when a cell divides
Cytoplasm	All of the material inside the plasma membrane of a cell (excluding organelles)
Cytoskeleton	Structure of filaments and tubules in the cytoplasm that provides a cell with an internal framework
Dead Zone	Area in the ocean or other body of water where low oxygen levels from excessive growth of algae have killed all aquatic organisms
Deciduous Plant	Type of plant that seasonally loses its leaves to reduce water loss during the cold or dry season each year and grows new leaves later in the year
Decomposer	Organism that breaks down the remains of dead organisms and other organic wastes
Demographic Transition	Changes in population that occurred in Europe and North America beginning in the 18th century, in which death rates fell and population growth rates increased, followed by birth rates falling and population growth rates decreasing
Dendrite	Extension of the cell body of a neuron that receives nerve impulses from other neurons
Dependent Variable	Variable in a scientific experiment that is affected by another variable, called the independent variable
Deposit Feeder	Animal that obtains organic matter for nutrition by eating soil or the sediments at the bottom of a body of water
Dermal Tissue	Type of plant tissue that covers the outside of a plant in a single layer of cells called the epidermis
Dermis	Lower layer of the skin that is made of tough connective tissue and contains blood vessels, nerve endings, hair follicles, and glands
Detritivore	Decomposer that consumes detritus
Detritus	Substance composed of dead leaves, other plant remains, and animal feces that collects on the soil or at the bottom of a body of water
Dialysis	Medical procedure in which blood is filtered through a machine in patients with kidney failure
Diaphragm	Large, sheet-like muscle below the lungs that allows breathing to occur when it contracts and relaxes
Differentiation	Process by which unspecialized cells become specialized into one of many different types of cells, such as neurons or epithelial cells
Diffusion	Type of passive transport that does not require the help of transport proteins
Digestion	Process of breaking down food into nutrients that can be absorbed by the blood
Digestive System	Organ system that breaks down food, absorbs nutrients, and eliminates any remaining waste
Diploid	Having two of each type of chromosome
Directional Selection	Type of natural selection for a polygenic trait in which one of two extreme phenotypes is selected for, resulting in a shift of the phenotypic distribution toward that extreme
Dispersal	Movement of offspring away from their parents
Disruptive Selection	Type of natural selection for a polygenic trait in which phenotypes in the middle of the phenotypic distribution are selected against, resulting in two overlapping phenotypes, one at each end of the distribution
DNA (Deoxyribonucleic Acid)	Double-stranded nucleic acid that makes up genes and chromosomes
DNA Replication	Process of copying of DNA prior to cell division
Domain	Taxon in the revised Linnaean system that is larger and more inclusive than the kingdom
Dominant Allele	Allele that masks the presence of another allele for the same gene when they occur together in a heterozygote
Dormancy	State in which a plant slows down cellular activity and may shed its leaves
Double Helix	Double spiral shape of the DNA molecule
Drug Abuse	Use of a drug without the advice of a medical professional and for reasons not originally intended
Drug Addiction	Situation in which a drug user is unable to stop using a drug
Eating Disorder	Mental illness in which people feel compelled to eat in a way that causes physical, mental, and emotional health problems
Echinoderms	Invertebrates such as sea stars and sand dollars that are characterized by a spiny endoskeleton, radial symmetry as adults, and a water vascular system
Ecological Succession	Changes through time in the numbers and types of species that make up the community of an ecosystem
Ecology	Branch of biology that is the study of how living things interact with each other and with their environment
Ecosystem	All the living things in a given area together with the physical factors of the nonliving environment
Ectoderm	Outer embryonic cell layer in animals
Ectothermy	Regulation of body temperature from the outside through behavioral changes such as basking in the sun
Egg	Female gamete
Ejaculation	Muscle contractions that propel sperm from the epididymes and out through the urethra in males
Electron Transport Chain	Series of electron-transport molecules that pass high-energy electrons from molecule to molecule and capture their energy
Element	Pure substance that cannot be broken down into other types of substances
Elimination	Process in which waste passes out of the body
Embryo	Stage of growth and development that occurs from implantation through the eighth week after fertilization in humans
Emigration	Movement of individuals out of a population
Emphysema	Lung disease, usually caused by smoking, in which walls of alveoli break down, so less gas can be exchanged in the lungs
Endocrine System	Human body system of glands that release hormones into the blood
Endocytosis	Type of vesicle transport that moves substances into a cell
Endoderm	Inner embryonic cell layer in animals
Endoplasmic Reticulum (ER)	Organelle in eukaryotic cells that helps make and transport proteins
Endoskeleton	Internal skeleton that provides support and protection
Endosperm	Stored food inside a plant seed
Endospore	Spores that form inside prokaryotic cells when they are under stress, enclosing the DNA and helping it survive conditions that may kill the cell
Endosymbiotic Theory	Theory that eukaryotic organelles such as mitochondria evolved from ancient, free-living prokaryotes that invaded primitive eukaryotic cells
Endothermic Reaction	Chemical reaction that absorbs energy
Endothermy	Regulation of body temperature from the inside through metabolic or other physical changes
Energy	Ability to do work
Enzyme	Protein that speeds up biochemical reactions
Epidermis	Outer layer of skin that consists mainly of epithelial cells and lacks nerve endings and blood vessels
Epididymis (Plural, Epididymes)	One of two male reproductive organs where sperm mature and are stored until they leave the body
Epiphyte	Plant that is adapted to grow on other plants and obtain moisture from the air
Epistasis	Situation in which one gene affects the expression of another gene
Epithelial Tissue	Tissue made up of cells that line inner and outer body surfaces, such as skin
Esophagus	Long, narrow digestive organ that passes food from the pharynx to the stomach
Estrogen	Female sex hormone secreted by the ovaries
Estuary	A partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the ocean
Ethology	Branch of biology that studies animal behavior
Eukaryote	Organism that has cells containing a nucleus and other organelles
Eukaryotic Cell	Cell that contains a nucleus and other organelles
Evaporation	Process in which liquid water changes to water vapor
Evergreen Plant	Type of plant that keeps its leaves and stays green year-round
Evidence	Any type of data that may be used to test a hypothesis
Evolution	Change in the characteristics of living things over time; the change in species over time
Exchange Pool	Part of a biogeochemical cycle that holds an element or water for a short period of time
Excretion	Process of removing wastes and excess water from the body
Excretory System	Organ system that removes wastes and excess water from the body and includes the kidneys, large intestine, liver, skin, and lungs
Exocytosis	Type of vesicle transport that moves substances out of a cell
Exoskeleton	Non-bony skeleton that forms on the outside of the body of some invertebrates and provides protection and support
Exothermic Reaction	Chemical reaction that releases energy
Exotic Species	Species that is introduced (usually by human actions) into a new habitat where it may lack local predators and out-compete native species
Experiment	Special type of scientific investigation that is performed under controlled conditions
Exponential Growth	Pattern of population growth in which a population starts out growing slowly but grows faster and faster as population size increases
Extinction	Situation in which a species completely dies out and no members of the species remain
Extremophile	Any type of Archaea that lives in an extreme environment, such as a very salty, hot, or acidic environment
Facilitated Diffusion	Diffusion with the help of transport proteins
Fallopian Tube	One of two female reproductive organs that carry eggs from the ovary to the uterus and provide the site where fertilization usually takes place
Feces	Solid waste that remains after food is digested and is eliminated from the body through the anus
Fermentation	Type of anaerobic respiration that includes glycolysis followed by the conversion of pyruvic acid to one or more other compounds and the formation of NAD+
Fertilization	Union of two gametes that produces a diploid zygote
Fetus	Developing human organism between weeks 8 and 38 after fertilization
Fibrous Root	Threadlike root that makes up part of the fibrous root system of some plants
Filter Feeder	Animal that obtains organic matter for nutrition by filtering particles out of water
Fish	Ectothermic, aquatic vertebrate with a streamlined body and gills for absorbing oxygen from water
Fitness	Relative ability of an organism to survive and produce fertile offspring
Flagella (Singular, Flagellum)	Long, thin protein extensions of the plasma membrane in most prokaryotic cells that help the cells move
Flagellate	Type of protozoa, such as Giardia, that moves with flagella
Flower	Structure in angiosperms consisting of male and female reproductive structures that attracts animal pollinators
Follicle-Stimulating Hormone (FSH)	Pituitary gland hormone that stimulates the ovaries to secrete estrogen and follicles in the ovaries to mature
Food	Organic molecules such as glucose that organisms use for chemical energy
Food Chain	Diagram that represents a single pathway through which energy and matter flow through an ecosystem
Food Web	Diagram that represents multiple intersecting pathways through which energy and matter flow through an ecosystem
Fossil	Preserved remains or traces of organisms that lived in the past
Fossil Record	The record of life as told by the study and analysis of fossils
Frameshift Mutation	Deletion or insertion of one or more nucleotides that changes the reading frame of the genetic material
Freshwater Biome	Aquatic biome such as a pond, lake, stream, or river in which the water contains little or no salt
Fruit	Structure in many flowering plants that develops from the ovary and contains seeds
Fungi (Singular, Fungus)	Kingdom in the domain Eukarya that includes molds, mushrooms, and yeasts
Galápagos Islands	Group of 16 small volcanic islands in the Pacific Ocean 966 kilometers (600 miles) off the west coast of South America, where Darwin made some of his most important observations during his voyage on the HMS Beagle
Gall Bladder	Sac-like organ that stores bile from the liver and secretes it into the duodenum of the small intestine
Gamete	Reproductive cell produced during meiosis that has the haploid number of chromosomes
Gametogenesis	Development of haploid cells into gametes such as sperm and egg
Gametophyte	Haploid generation in the life cycle of a plant that results from asexual reproduction with spores and that produces gametes for sexual reproduction
Gastrointestinal (GI) Tract	Organs of the digestive system through which food passes during digestion, including the mouth, esophagus, stomach, and small and large intestines
Gene	Unit of DNA on a chromosome that is encoded with the instructions for a single protein
Gene Cloning	Process of isolating and making copies of a gene
Gene Expression	Use of a gene to make a protein
Gene Flow	Change in allele frequencies that occurs when individuals move into or out of a population
Gene Pool	All the genes of all the members of a population
Generalist	Organism that can consume many different types of food
Gene Theory	Theory that the characteristics of living things are controlled by genes that are passed from parents to offspring
Gene Therapy	Way to cure genetic disorders by inserting normal genes into cells with mutant genes
Genetic Code	Universal code of three-base codons that encodes the genetic instructions for the amino acid sequence of proteins
Genetic Disorder	Disease caused by a mutation in one or a few genes
Genetic Drift	A random change in allele frequencies that occurs in a small population
Genetic Engineering	Using biotechnology to change the genetic makeup of an organism
Genetics	The science of heredity
Genetic Trait	Characteristic that is encoded in DNA
Genetic Transfer	Method of increasing genetic variation in prokaryotes that involves cells “grabbing” stray pieces of DNA from their environment or exchanging DNA directly with other cells
Genital Herpes	Sexually transmitted infection caused by a herpes virus that is characterized by periodic outbreaks of blisters on the genitals
Genital Warts	Small, rough growths on the genitals caused by a sexually transmitted infection with human papillomavirus (HPV)
Genotype	Alleles an individual inherits at a particular genetic locus
Genus	Taxon above the species in the Linnaean classification system; group of closely related species
Geologic Time Scale	Time line of Earth based on major events in geology, climate, and the evolution of life
Germination	Early growth and development of a plant embryo in a seed
Germline Mutation	Mutation that occur in gametes
Giardiasis	Disease caused by Giardia protozoa that spreads through contaminated food or water
Gills	Organs in aquatic organisms composed of thin filaments that absorb oxygen from water
Gizzard	Food-grinding organ in the digestive system of birds and some other animals that may contain swallowed stones
Global Warming	Recent rise in Earth’s average surface temperature generally attributed to an increased greenhouse effect
Glucose	Simple carbohydrate with the chemical formula C6H12O6 that is the nearly universal food for life
Glycolysis	First stage of cellular respiration in which glucose is split, in the absence of oxygen, to form two molecules of pyruvate (pyruvic acid) and two (net) molecules of ATP
Golgi Apparatus	Organelle in eukaryotic cells that processes proteins and prepares them for use both inside and outside the cell
Gonads	Glands that secrete sex hormones and produce gametes; testes in males and ovaries in females
Gonorrhea	Common sexually transmitted infection that is caused by bacteria
Gradualism	Model of the timing of evolution in which evolutionary change occurs at a slow and steady pace
Gram-Negative Bacteria	Type of bacteria that stain red with Gram stain and have a thin cell wall with an outer membrane
Gram-Positive Bacteria	Type of bacteria that stain purple with Gram stain and have a thick cell wall without an outer membrane
Grana	Within the chloroplast, consists of sac-like membranes, known as thylakoid membranes
Greenhouse Effect	Natural feature of Earth’s atmosphere that occurs when gases in the atmosphere radiate the sun’s heat back down to Earth’s surface, making Earth’s temperature far warmer than it otherwise would be
Ground Tissue	Type of plant tissue making up most of the interior of the roots and stems of plants that carries out basic metabolic functions and provides support and storage
Groundwater	Water that exists in the ground either in the soil or in rock layers below the surface
Growing Season	Period of time each year when it is warm enough and wet enough for plants to grow
Gymnosperm	Type of seed plant that produces bare seeds in cones
Habitat	Physical environment in which a species lives and to which it has become adapted
Habitat Loss	Destruction or disruption of Earth’s natural habitats, most often due to human actions such as agriculture, forestry, mining, and urbanization
Hair Follicle	Structure in the dermis of skin where a hair originates
Haploid	Having only one chromosome of each type
Hardy-Weinberg Theorem	Founding principle of population genetics that proves allele and genotype frequencies do not change in a population that meets the conditions of no mutation, no migration, large population size, random mating, and no natural selection
Heart	Muscular organ in the chest that that pumps blood through blood vessels when it contracts
Heart Attack	Blockage of blood flow to heart muscle tissues that may result in the death of cardiac muscle fibers
Hepatitis B	Inflammation of the liver caused by infection with hepatitis B virus, which is often transmitted through sexual contact
Herbivore	Consumer that eats producers such as plants or algae
Heterotroph	Organism that gets food by consuming other organisms
Heterozygote	Organism that inherits two different alleles for a given gene
Homeobox Gene	Gene that codes of regulatory proteins that control gene expression during development
Homeostasis	Process of maintaining a stable environment inside a cell or an entire organism
Homologous Chromosomes	Pair of chromosomes that have the same size and shape and contain the same genes
Homologous Structure	Structure that is similar in related organisms because it was inherited from a common ancestor
Homozygote	Organism that inherits two alleles of the same type for a given gene
Host	Species that is harmed in a parasitic relationship
Human Genome	All of the DNA of the human species
Human Genome Project	International science project that sequenced all 3 billion base pairs of the human genome
Human Immunodeficiency Virus (HIV)	Virus transmitted through body fluids that infects and destroys helper T cells and eventually causes acquired immunodeficiency syndrome (AIDS)
Human Papilloma Virus (HPV)	Sexually transmitted virus that causes genital warts and cervical cancer
Humoral Immune Response	Type of immune response in which B cells produce antibodies against antigens in blood and lymph
Hybrid	Offspring that results from a cross between two different types of parents
Hydrogen Bond	Type of chemical bond that forms between molecules: found between water molecules
Hydrostatic Skeleton	Type of internal support in an animal body that results from the pressure of fluid within the body cavity known as the coelom
Hypertension	High blood pressure
Hyphae (Singular, Hypha)	Thread-like filaments that make up the body of a fungus and consist of one or more cells surrounded by a tubular cell wall
Hypothalamus	Part of the brain that secretes hormones
Hypothesis	Possible answer to a scientific question; must be falsifiable
Immigration	Movement of individuals into a population
Immune Response	Specific defense against a particular pathogen
Immune System	Body system that consists of skin, mucous, membranes, and other tissues and organs that defends the body from pathogens and cancer
Immunity	Ability to resist a pathogen due to memory lymphocytes or antibodies to the antigens the pathogen carries
Immunization	Deliberate exposure of a person to a pathogen in order to provoke an immune response and the formation of memory cells specific to that pathogen
Immunodeficiency	Inability of the immune system to fight off pathogens that a normal immune system would be able to resist
Implantation	Process in which a blastocyst embeds in the endometrium lining the uterus
Incomplete Digestive System	Digestive system that consists of a digestive cavity and a single opening that serves as both mouth and anus
Incomplete Dominance	Relationship between the alleles for a gene in which one allele is only partly dominant to the other allele so an intermediate phenotype results
Incubation	Period of bird reproduction when one or both parents sit on, or brood, the eggs in order to keep them warm until they hatch
Independent Assortment	Independent segregation of chromosomes to gametes during meiosis
Independent Variable	Variable in a scientific experiment that is manipulated by the researcher to investigate its effect on another variable called the dependent variable
Infancy	First year of life after birth in humans
Inflammatory Response	Nonspecific response the body first makes to tissue damage or infection
Inheritance Of Acquired Characteristics	Mistaken idea of Jean Baptiste Lamarck that evolution occurs through the inheritance of traits that an organism develops in its own life time
Innate Behavior	Behavior closely controlled by genes that occurs naturally, without learning or practice, in all members of a species whenever they are exposed to a certain stimulus; also called instinctive behavior
Instinct	Ability of an animal to perform a behavior the first time it is exposed to the proper stimulus
Integumentary System	Human body system that includes the skin, nails, and hair
Interneuron	Type of neuron that carries nerve impulses back and forth between sensory and motor neurons
Interphase	Stage of the eukaryotic cell cycle when the cell grows, synthesizes DNA, and prepares to divide
Interspecific Competition	Relationship between organisms of different species that strive for the same resources in the same place
Intertidal Zone	In marine biomes, the narrow strip along the coastline that is covered by water at high tide and exposed to air at low tide
Intraspecific Competition	Relationship between organisms of the same species that strive for the same resources in the same place
Invertebrate	Animal that lacks a vertebral column, or backbone
Joint	Place where two or more bones of the skeleton meet
Kelp	Multicellular seaweed that may grow as large as a tree and occurs in forests found throughout the ocean in temperate and arctic climates
Keratin	Tough, fibrous protein in skin, nails, and hair
Keystone Species	Species that plays an especially important role in its community so that major changes in its numbers affect the populations of many other species in the community
Kidney	Main organ of the excretory system that filters blood and forms urine
Kidney Failure	Loss of the ability of nephrons of the kidney to function fully
Kingdom	Largest and most inclusive taxon in the original Linnaean classification system
Krebs Cycle	Second stage of aerobic respiration in which two pyruvate (pyruvic acid) molecules from the first stage react to form ATP, NADH, and FADH2
K-Selected	Species in which population growth is controlled by density-dependent factors and population size is generally at or near carrying capacity
Lactation	Production of milk for an offspring by mammary glands, which occurs in all female mammals after giving birth or laying eggs
Lactic Acid Fermentation	Type of anaerobic respiration that includes glycolysis followed by the conversion of pyruvic acid to lactic acid and the formation of NAD+
Lancelets	Members of the subphylum Cephalochordata
Large Intestine	Organ of the digestive system that removes water from food waste and forms feces
Larva (Plural, Larvae)	Juvenile stage that occurs in the life cycle of many invertebrates, fish, and amphibians and that differs in form and function from the adult stage
Larynx	Organ of the respiratory system between the pharynx and trachea that is also called the voice box because it allows the production of vocal sounds
Last Universal Common Ancestor (LUCA)	Hypothetical early cell (or group of cells) that gave rise to all subsequent life on Earth
Latency	Period of dormancy of a virus inside a living body that may last for many years
Law Of Independent Assortment	Mendel’s second law stating that factors controlling different characteristics are inherited independently of each other
Law Of Segregation	Mendel’s first law stating that the two factors controlling a characteristics separate and go to different gametes
Learning	Change in behavior that occurs as a result of experience
Leukocyte	White blood cell produced by bone marrow to fight infections
Lichen	An organism that results from a mutualistic relationship between a fungus and a cyanobacterium or green alga
Life Cycle	Series of stages a sexually reproducing organism goes through from one generation to the next
Ligament	Band of fibrous connective tissue that holds bones together
Light Reactions	First stage of photosynthesis in which light energy from the sun is captured and changed into chemical energy that is stored in ATP and NADPH
Lignin	Tough, hydrophobic carbohydrate molecule that stiffens and waterproofs vascular tissues of plants
Linkage Map	Map that shows the positions of genes on a chromosome based on the frequency of crossing-over between the genes
Linked Genes	Genes that are located on the same chromosome
Linnaean Classification System	System of classifying organisms based on observable physical traits; consists of a hierarchy of taxa, fro the kingdom to the species
Lipid	Organic compound such as fat or oil
Liver	Organ of digestion and excretion that secretes bile for lipid digestion and breaks down excess amino acids and toxins in the blood
Locus	Position of a gene on a chromosome
Logistic Growth	Pattern of population growth in which growth slows and population size levels off as the population approaches the carrying capacity
Lung	Organ of the respiratory system in which gas exchange takes place between the blood and the atmosphere
Luteinizing Hormone (LH)	Pituitary gland hormone that stimulates the testes to secrete testosterone and the ovaries to secrete estrogen
Lymph	Fluid that leaks out of capillaries into spaces between cells and circulates in the vessels of the lymphatic system
Lymphatic System	System of the body consisting of organs, vessels, nodes, and lymph that produces lymphocytes and filters pathogens from body fluids
Lymph Node	Small structures located on lymphatic vessels where pathogens are filtered from lymph and destroyed by lymphocytes
Lymphocyte	Type of leukocyte that is a key cell in the immune response to a specific pathogen
Macroevolution	Evolutionary change that occurs over geologic time above the level of the species
Macronutrient	Nutrient such as carbohydrates, proteins, lipids, or water that is needed by the body in relatively large amounts
Malaria	Disease caused by Plasmodium protozoa and transmitted by mosquitoes in tropical and subtropical regions of the world
Mammal	Endothermic, tetrapod vertebrate that lays amniotic eggs and has mammary glands (in females) and hair or fur
Mammary Gland	Gland in female mammals that produces milk for offspring
Mantle	Layer of tissue that lies between the shell and body of a mollusk and forms a cavity, called the mantle cavity, that pumps water for filter feeding
Marine Biome	Aquatic biome in the salt water of the ocean
Marsupial	Therian mammal in which the embryo is born at an early, immature stage and completes its development outside the mother’s body in a pouch on her belly
Mass Extinction	Extinction event in which many if not most species abruptly disappear from Earth
Matter	Anything that takes up space and has mass
Mechanical Digestion	Physical breakdown of chunks of food into smaller pieces by organs of the digestive system
Medusa (Plural, Medusae)	Basic body plan in cnidarians such as jellyfish that is bell-shaped and typically motile
Meiosis	Type of cell division in which the number of chromosomes is reduced by half and four haploid cells result
Melanin	Brown pigment produced by melanocytes in the skin that gives skin most of its color and prevents UV light from penetrating the skin
Memory Cell	Lymphocyte (B or T cell) that retains a “memory” of a specific pathogen after an infection is over and thus provides immunity to the pathogen
Menarche	Beginning of menstruation; first monthly period in females
Menopause	Period during which menstrual cycles slow down and eventually stop in middle adulthood
Menstrual Cycle	Monthly cycle of processes and events in the ovaries and uterus of a sexually mature human female
Menstruation	Process in which the endometrium of the uterus is shed from the body during the first several days of the menstrual cycle; also called monthly period
Meristem	Type of plant tissue consisting of undifferentiated cells that can continue to divide and differentiate and from which plants grow in length or width
Mesoderm	Embryonic cell layer in many animals that is located between the endoderm (inner cell layer) and ectoderm (outer cell layer)
Mesophyll	Specialized tissue inside plant leaves where photosynthesis takes place
Mesozoic Era	Age of dinosaurs that lasted from 245–65 million years ago
Messenger RNA (Mrna)	Type of RNA that copies genetic instructions from DNA in the nucleus and carries them to the cytoplasm
Metabolism	Sum of all the biochemical reactions in an organism
Metamorphosis	Process in which a larva undergoes a major transformation to change into the adult form, which occurs in amphibians, arthropods, and other invertebrates
Metaphase	Second phase of mitosis during which chromosomes line up at the equator of the cell
Microevolution	Evolutionary change that occurs over a relatively short period of time within a population or species
Micronutrient	Nutrient such as a vitamin or mineral that is needed by the body in relatively small amounts
Migration	Regular movement of individuals or populations each year during certain seasons, usually to find food, mates, or other resources
Mineral	Chemical element such as calcium or potassium that is needed in relatively small amounts for proper body functioning
Mitochondria (Singular, Mitochondrion)	Organelle in eukaryotic cells that makes energy available to the cell in the form of ATP molecules
Mitosis	Process in which the nucleus of a eukaryotic cell divides
Model	Representation of part of the real world
Molecular Clock	Using DNA (or proteins) to measure how long it has been since related species diverged from a common ancestor
Mollusca	Phylum of invertebrates that are generally characterized by a hard outer shell, a mantle, and a feeding organ called a radula
Molting	Process in which an animal sheds and replaces the outer covering of the body, such as the exoskeleton in arthropods
Monosaccharide	Simple sugar such as glucose that is a building block of carbohydrates
Monotreme	Type of mammal that reproduces by laying eggs
Motility	The ability to move
Motor Neuron	Type of neuron that carries nerve impulses from the central nervous system to muscles and glands
Mucous Membrane	Epithelial tissue that lines inner body surfaces and body openings and produces mucus
Mucus	Slimy substance produced by mucous membranes that traps pathogens, particles, and debris
Multiple Allele Trait	Trait controlled by one gene with more than two alleles
Muscle Fiber	Long, thin muscle cell that has the ability to contract, or shorten
Muscle Tissue	Tissue made up of cells that can contract; includes smooth, skeletal, and cardiac muscle tissue
Muscular System	Human body system that includes all the muscles of the body
Mutagen	Environmental factors that causes mutations
Mutation	Change in the sequence of bases in DNA or RNA
Mutualism	Type of symbiotic relationship in which both species benefit
Mycelium	Body of a fungus that consists of a mass of threadlike filaments called hyphae
Mycorrhiza	Mutualistic relationship between a plant and a fungus that grows in or on its roots
Myelin Sheath	Lipid layer around the axon of a neuron that allows nerve impulses to travel more rapidly down the axon
Myplate	Visual guideline for balanced eating, replacing mypyramid in 2011
Mypyramid	Visual dietary guideline that shows the relative amounts of foods in different food groups that should be eaten each day
Natural Resource	Something supplied by nature that helps support life
Natural Selection	Evolutionary process in which some living things produce more offspring than others so the characteristics of organisms change over time
Nature-Nurture Debate	Debate over the extent to which genes (nature) or experiences in a given environment (nurture) control traits such as animal behaviors
Nectar	Sweet, sugary liquid produced by the flowers of many angiosperms to attract animal pollinators
Nematoda	Phylum of invertebrates called roundworms, which have a pseudocoelom and complete digestive system
Neocortex	Layer of nerve cells covering the cerebrum of the mammalian brain that plays an important role in many complex brain functions
Nephron	Structural and functional unit of the kidney that filters blood and forms urine
Nerve	One of many cable-like bundles of axons that make up the peripheral nervous system
Nerve Impulse	Electrical signal transmitted by the nervous system
Nervous System	Human body system that carries electrical messages throughout the body
Nervous Tissue	Tissue made up of neurons, or nerve cells, that carry electrical messages
Neuron	Nerve cell; structural and functional unit of the nervous system
Neurotransmitter	Chemical that carries a nerve impulse from one nerve to another at a synapse
Niche	Role of a species in its ecosystem that includes all the ways the species interacts with the biotic and abiotic factors of the ecosystem
Nitrogen Cycle	Interconnected pathways through which nitrogen is recycled through the biotic and abiotic components of the biosphere
Nitrogen Fixation	Process of changing nitrogen gas to nitrates that is carried out by nitrogen-fixing bacteria in the soil or in the roots of legumes
Nondisjunction	Failure of replicated chromosomes to separate during meiosis II, resulting in some gametes with a missing chromosome and some with an extra chromosome
Nonrenewable Resource	Natural resource that exists in a fixed amount and can be used up
Notochord	Stiff support rod that runs from one end of the body to the other in animals called chordates
Nucleic Acid	Organic compound such as DNA or RNA
Nucleotide	Small molecule containing a sugar, phosphate group, and base that is a building block of nucleic acids
Nucleus (Plural, Nuclei)	Organelle inside eukaryotic cells that contains most of the cell’s DNA and acts as the control center of the cell
Nutrient	Substance the body needs for energy, building materials, or control of body processes
Obesity	Condition in which the body mass index is 30.0 kg/m2 or greater
Observation	Anything that is detected with the senses
Omnivore	Consumer that eats both plants and animals
Oogenesis	Process of producing eggs in the ovary
Open Circulatory System	Type of circulatory system in which blood flows not only through blood vessels but also through a body cavity
Operator	A region of an operon where regulatory proteins bind
Operon	Region of prokaryotic DNA that consists of a promoter, an operator, and one or more genes that encode proteins needed for a specific function
Organ	Structure composed of more than one type of tissue that performs a particular function
Organelle	Structure within the cytoplasm of a cell that is enclosed within a membrane and performs a specific job
Organic Compound	Compound found in living things that contains mainly carbon
Organism	An individual living thing
Organ System	Group of organs that work together to do a certain job
Osmosis	Diffusion of water molecules across a membrane
Ossification	Process in which mineral deposits replace cartilage and change it into bone
Osteoblast	Type of bone cell that makes new bone cells and secretes collagen
Osteoclast	Type of bone cell that dissolves minerals in bone and releases them back into the blood
Osteocyte	Type of bone cell that regulates mineral homeostasis by directing the uptake of minerals from the blood and the release of minerals back into the blood as needed
Ovary	One of two female reproductive organs that produces eggs and secretes estrogen
Ovipary	Type of reproduction in which an embryo develops within an egg outside the mother’s body
Ovovivipary	Type of reproduction in which an embryo develops inside an egg within the mother’s body but in which the mother provides no nourishment to the developing embryo in the egg
Ovulation	Release of a secondary oocyte from the uterus about half way through the menstrual cycle
Ozone Hole	Hole in the ozone layer high in the atmosphere over Antarctica caused by air pollution destroying ozone
Paleontologist	Scientist who finds and studies fossils to learn about evolution and understand the past
Paleozoic Era	Age of “old life” from 544–245 million years ago that began with the Cambrian explosion and ended with the Permian extinction
Pancreas	Gland near the stomach that secretes insulin and glucagon to regulate blood glucose and enzymes to help digest food
Parasite	Species that benefits in a parasitic relationship
Parasitism	Symbiotic relationship in which one species benefits while the other species is harmed
Parathyroid Glands	A pair of small glands in the neck that secretes hormones that regulate blood calcium
Passive Immunity	Type of immunity to a particular pathogen that results when antibodies are transferred to a person who has never been exposed to the pathogen
Passive Transport	Movement of substances across a plasma membrane that does not require energy
Pathogen	Disease-causing agent such as a bacterium, virus, fungus, or protozoan
Pedigree	Chart showing how a trait is passed from generation to generation within a family
Penis	Male reproductive organ containing the urethra, through which sperm and urine pass out of the body
Periosteum	Tough, fibrous membrane that covers the outer surface of bone
Peripheral Nervous System (PNS)	One of two major divisions of the nervous system that consists of all the nervous tissue that lies outside the central nervous system
Peristalsis	Rapid, involuntary, wave-like contraction of muscles that pushes food through the GI tract and urine through the ureters
Permian Extinction	Extinction at the end of the Paleozoic Period that was the biggest mass extinction the world had ever seen until then
Petal	Outer parts of flowers that are usually brightly colored to attract animal pollinators
Ph	Scale that is used to measure acidity
Phagocytosis	Process in which leukocytes engulf and break down pathogens and debris
Pharmacogenomics	Field that is tailoring medical treatments to fit our genetic profiles
Pharynx	Long, tubular organ that connects the mouth and nasal cavity with the larynx through which air and food pass
Phenotype	Characteristics of an organism that depend on how the organism’s genotype is expressed
Phloem	Type of vascular tissue in a plant that transports food from photosynthetic cells to other parts of the plant
Phospholipid Bilayer	Double layer of phospholipid molecules that makes up a plasma membrane
Photic Zone	Area in an aquatic biome that extends to a maximum depth of 200 meters
Photoautotroph	Producer that uses energy from sunlight to make food by photosynthesis
Photosynthesis	Process of using the energy in sunlight to make food (glucose)
Photosystem	Group of molecules, including chlorophyll, in the thylakoid membrane of a chloroplast that captures light energy
Phylogenetic Tree	Diagram that shows how species are related to each other through common ancestors
Phylogeny	Evolutionary history of a group of related organisms
Phytoplankton	Bacteria and algae that use sunlight to make food
Pineal Gland	Gland of the endocrine system that secretes the hormone melatonin that regulates sleep-wake cycles
Pioneer Species	Type of species that first colonizes a disturbed area
Pistil	Female reproductive structure of a flower that consists of a stigma, style, and ovary
Pituitary Gland	Master gland of the endocrine system that secretes many hormones, the majority of which regulate other endocrine glands
Placenta	Temporary organ that consists of a large mass of maternal and fetal blood vessels through the mother’s and fetus’s blood exchange substances
Placental Mammal	Therian mammal in which a placenta develops during pregnancy to sustain the fetus while it develops inside the mother’s uterus
Plant	Multicellular eukaryote with chloroplasts, cell walls made of cellulose, and specialized reproductive organs
Plasma	Golden-yellow fluid part of blood that contains many dissolved substances and blood cells
Plasma Membrane	Thin coat of lipids (phospholipids) that surrounds and encloses a cell
Plasmid	Small, circular piece of DNA in a prokaryotic cell
Platelet	Cell fragment in blood that helps blood clot
Platyhelminthes	Invertebrate phylum of flatworms that are characterized by a flat body because they lack a coelom or pseudocoelom
Pleiotropy	Situation in which a single gene affects more than one trait
Pneumonia	Disease in which the alveoli of the lungs become inflamed and filled with fluid as a result of infection or injury
Point Mutation	Change in a single nucleotide base in the genetic material
Polarity	Difference in electrical charge between different parts of the same molecule
Pollen	Tiny grains that bear the male gametes of seed plants and transfer sperm to female reproductive structures
Pollination	Fertilization in plants in which pollen is transferred to female gametes in an ovary
Polygenic Characteristic	Characteristic, or trait, controlled by more than one gene, each of which may have two or more alleles
Polymerase Chain Reaction (PCR)	Biotechnology process that makes many copies of a gene or other DNA segment
Polynucleotide	Chain of nucleotides that alone or with another such chain makes up a nucleic acid
Polyp	Basic body plan in cnidarians such as jellyfish that is tubular in shape and typically sessile
Polypeptide	Chain of amino acids that alone or with other such chains makes up a protein
Polysaccharide	Chain of monosaccharides that makes up a complex carbohydrate such as starch
Population	All the organisms of the same species that live in the same area
Population Density	Average number of individuals in a population per unit of area or volume
Population Distribution	Describes how the individuals are distributed, or spread throughout their habitat
Population Genetics	Science focusing on evolution within populations that is the area of overlap between evolutionary theory and Mendelian genetics
Population Growth Rate (R)	How fast a population changes in size over time
Population Pyramid	Bar graph that represents the age-structure of a population
Porifera	Invertebrate phylum of sponges, which have a non-bony endoskeleton and are sessile as adults
Precipitation	Water that falls from clouds in the atmosphere to Earth’s in the form of rain, snow, sleet, hail, or freezing rain
Predation	Relationship in which members of one species consume members of another species
Predator	Species that consumes another in a predator-prey relationship
Prediction	Statement that tells what will happen under certain conditions
Pregnancy	Carrying of one or more offspring from fertilization until birth
Prey	Species that is consumed by another in a predator-prey relationship
Primary Succession	Change in the numbers and types of species that live in a community that occurs in an area that has never before been colonized
Probability	The likelihood, or chance, than a certain event will occur
Producer	Organism that produces food for itself and other organisms
Product	Substance that forms as the result of a chemical reaction
Prokaryote	Single-celled organism that lacks a nucleus
Prokaryotic Cell	Cell without a nucleus that is found in single-celled organisms
Promoter	Region of a gene where a RNA polymerase binds to initiate transcription of the gene
Prophase	First phase of mitosis during which chromatin condense into chromosomes, the nuclear envelope breaks down, centrioles separate, and a spindle begins to form
Protein	Organic compound made up of amino acids
Protein Synthesis	Process in which cells make proteins that includes transcription of DNA and translation of mrna
Protist	Kingdom in the domain Eukarya that includes all eukaryotes except plants, animals, and fungi
Protozoa (Singular, Protozoan)	Animal-like protists such as Amoeba and Paramecium
Pseudocoelom	Partial, fluid-filled cavity inside the body of some invertebrates
Pseudopod	Temporary, foot-like extension of the cytoplasm that some cells use for movement or feeding
Psychoactive Drug	Drug that affects the central nervous system, generally by influencing the transmission of never impulses in the brain
Puberty	Period during which humans become sexually mature
Pulmonary Circulation	Part of the circulatory system that carries blood between the heart and lungs
Punctuated Equilibrium	Model of the timing of evolution in which long periods of little evolutionary change are interrupted by bursts of rapid evolutionary change
Punnett Square	Chart for determining the expected percentages of different genotypes in the offspring of two parents
Pupa	Life cycle stage of many insects that occurs between the larval and adult stages and during which the insect is immobile, may be encased within a cocoon, and changes into the adult form
Radial Symmetry	Symmetry of a body plan in which there is a distinct top and bottom but not distinct head and tail ends, so the body can be divided into two halves like a pie
Reactant	Starting material in a chemical reaction
Recessive Allele	Allele that is masked by the presence of another allele for the same gene when they occur together in a heterozygote
Recombinant DNA	DNA that results when DNA from two organisms is combined
Red Blood Cell	Type of cell in blood that contains hemoglobin and carries oxygen
Reflex	Rapid motor response to a sensory stimulus in which nerve impulses travel in an arc that includes the spinal cord but not the brain
Regeneration	Regrowing of tissues, organs, or limbs that have been lost or damaged
Regulatory Element	Region of DNA where a regulatory protein binds
Regulatory Protein	Protein that regulates gene expression
Relative Dating	Method of dating fossils by their location in rock layers; determines which fossils are older or younger but not their age in years
Renewable Resource	Natural resource that can be replenished by natural processes as quickly as humans use it
Reproduction	Process by which living things give rise to offspring
Reproductive System	System of organs that produces gametes and secretes sex hormones
Reptile	Ectothermic, tetrapod vertebrate that lays amniotic eggs; includes crocodiles, lizards, snakes, and turtles
Reservoir	Part of a biogeochemical cycle that holds an element or water for a long period of time
Respiration	Exchange of gases between the body and the outside air
Respiratory System	Organ system that brings oxygen into the body and releases carbon dioxide into the atmosphere
Resting Potential	Difference in electrical charge across the plasma membrane of a neuron that is not actively transmitting a nerve impulse
Rhizoid	Hair-like structure in a nonvascular plant that absorbs water and minerals and anchors the plant to a surface
Ribosomal RNA	Type of RNA that helps form ribosomes and assemble proteins
Ribosome	Organelle inside all cells where proteins are made
Ringworm	Skin infection caused by the fungus Trichophyton that causes a characteristic ring-shaped rash
RNA (Ribonucleic Acid)	Single-stranded nucleic acid that helps make proteins
RNA World Hypothesis	Hypothesis that RNA was the first organic molecule to evolve and that early life was based on RNA, rather than DNA or protein
Root Hair	Tiny hairlike structure that extends from an epidermal cell of a plant root and increases the surface area for absorption
Root System	All the roots of a plant, including primary roots and secondary roots
R-Selected	Species in which population growth is rapid but death rates are high so population size is generally below the carrying capacity
Runoff	Precipitation that falls on land and flows over the surface of the ground
Saprotroph	Decomposer such as a fungus or protozoan that feeds on any remaining organic matter that is left after other decomposers do their work
Saturated Fatty Acid	Molecule in lipids in which carbon atoms are bonded to as many hydrogen atoms as possible
Sauropsid	Type of early amniote that evolved during the Carboniferous Period and eventually gave rise to dinosaurs, reptiles, and birds
Scavenger	Decomposer that consumers the soft tissues of dead animals
Science	Distinctive way of gaining knowledge about the natural world that tries to answer questions with evidence and logic
Scientific Investigation	Plan for asking questions and testing possible answers
Scientific Law	Statement describing what always happens under certain conditions in nature
Scientific Method	The process of a scientific investigation
Scientific Theory	Broad explanation that is widely accepted as true because it is supported by a great deal of evidence
Sebaceous Gland	Gland in the dermis of skin that produces sebum, an oily substance that waterproofs the skin and hair
Secondary Succession	Change in the numbers and types of species that live in a community that occurs in an area that was previously colonized but has been disturbed
Seed	Structure produced by a seed plant that contains an embryo and food supply enclosed within a tough coat
Seed Coat	Tough covering of a seed that protects the embryo and keeps it from drying out until conditions are favorable for germination
Segmentation	Division of an animal body into multiple segments
Semen	Fluid containing sperm and gland secretions that nourish sperm and carry them through the urethra and out of the body
Sensory Neuron	Type of neuron that carries nerve impulses from tissue and organs to the spinal cord and brain
Sensory Receptor	Specialized nerve cell that responds to a particular type of stimulus such as light or chemicals
Sepal	Part of a flower that helps protect it while it is still in bud
Sessile	Of or relating to an animal that is unable to move from place to place
Sex Chromosome	X or Y chromosome (in humans)
Sex Hormone	Chemical messenger that controls sexual development and reproduction
Sex-Linked Gene	Gene located on a sex chromosome
Sex-Linked Trait	Traits controlled by a gene located on a sex chromosome
Sexual Dimorphism	Differences between the phenotypes of males and females of the same species
Sexually Transmitted Infection (STI)	Infection caused by a pathogen that spreads mainly through sexual contact; also known as sexually transmitted disease (STD)
Sexual Reproduction	Type of reproduction that involves the fertilization of gametes produced by two parents and produces genetically variable offspring
Sixth Mass Extinction	Current mass extinction caused primarily by habitat loss due to human actions
Skeletal Muscle	Voluntary, striated muscle that is attached to bones of the skeleton and helps the body move
Skeletal System	Human body system that consists of all the bones of the body as well as cartilage and ligaments
Sliding Filament Theory	Theory that explains muscle contraction by the sliding of myosin filaments over actin filaments within muscle fibers
Slime Mold	Fungus-like protist commonly found on rotting logs and other decaying organic matter
Small Intestine	Long, narrow, tube-like organ of the digestive system where most chemical digestion of food and virtually all absorption of nutrients take place
Smooth Muscle	Involuntary, nonstriated muscle that is found in the walls of internal organs such as the stomach
Social Animal	Animal that lives in a society
Society	Close-knit group of animals of the same species that live and work together
Sodium-Potassium Pump	Type of active transport in which sodium ions are pumped out of the cell and potassium ions are pumped into the cell with the help of a carrier protein and energy from ATP
Soil	Mixture of eroded rock, minerals, organic matter, and other materials that is essential for plant growth and forms the foundation of terrestrial ecosystems
Solution	Mixture that has the same composition throughout
Somatic Mutation	Mutation that occurs in cells of the body other than gametes
Somatic Nervous System (SNS)	Division of the peripheral nervous system that controls voluntary, conscious activities and reflexes
Spawning	Depositing large numbers of gametes in the same place and at the same time by fish or amphibians
Specialization	Evolution of different adaptations in competing species, which allows them to live in the same area without competing
Speciation	Process by which a new species evolves
Species	Group of organisms that are similar enough to mate together and produce fertile offspring
Sperm	Male gamete
Spermatogenesis	Process of producing sperm in the testes
Spermatophyte	Type of plant that reproduces by producing seeds
Spinal Cord	Thin, tubular bundle of nervous tissue that extends from the brainstem down the back to the pelvis and connects the brain with the peripheral nervous system
Spongy Bone	Light, porous inner layer of bone that contains bone marrow
Sporangium (Plural, Sporangia)	Structure on a plant of the sporophyte generation that produces spores for asexual reproduction
Sporophyte	Diploid generation in the life cycle of a plant that results from sexual reproduction with gametes and that produces spores for asexual reproduction
Sporozoa (Singular, Sporozoan)	Type of protozoa that cannot move as adults
Stabilizing Selection	Type of natural selection for a polygenic trait in which phenotypes at both extremes of the phenotypic distribution are selected against, resulting in a narrowing of the range of phenotypic variation
Stamen	Male reproductive structure of a flower that consists of a stalk-like filament and a pollen-producing anther
Stimulus	Something that triggers a behavior
Stomach	Sac-like organ of the digestive system between the esophagus and small intestine in which both mechanical and chemical digestion take place
Stomata (Singular, Stoma)	Tiny pore in the epidermis of a plant leaf that controls transpiration and gas exchange with the air
Stroma	Space outside the thylakoid membranes of a chloroplast where the Calvin cycle of photosynthesis takes place
Sublimation	Process in which ice and snow change directly to water vapor
Survivorship Curve	Graph that represents the individuals still alive at each age in a population
Sustainable Use	Use of resources in a way that meets the needs of the present and also preserves the resources for the use of future generations
Sweat Gland	Gland in the dermis of skin that produces the salty fluid called sweat, which excretes wastes and helps cool the body
Swim Bladder	Balloon-like internal organ in most fish that can be used to move up or down through the water column by changing the amount of gas it contains
Symbiosis	Close relationship between organisms of different species in which at least one of the organisms benefits from the relationship
Sympatric Speciation	Evolution of a new species that occurs when without geographic separation first occurring between members of an original species
Synapse	Place where an axon terminal meets another cell
Synapsid	Type of early amniote that evolved during the Carboniferous Period and eventually gave rise to mammals
Synthetic Biology	Field of biology involved in engineering new functions from living systems
Syphilis	Sexually transmitted infection caused by bacteria that may eventually be fatal if untreated
Systemic Circulation	Part of the circulatory system that carries blood between the heart and body
Taproot	Single, thick primary root that characterizes the root system of some plants
Target Cell	Type of cell on which a particular hormone has an effect because it has receptor molecules for the hormone
TATA Box	Regulatory element that is part of the promoter of most eukaryotic genes
Taxa	A grouping of organisms in a classification system such as the Linnaean system; for example, species or genus
Taxonomy	Science of classifying organisms
T Cell	Type of lymphocyte involved in cell-mediated immunity in which cells infected with viruses are destroyed
Telophase	Last stage of mitosis during which chromosomes uncoil to form chromatin, the spindle breaks down, and new nuclear membranes form
Tendon	Tough connective tissue that attaches skeletal muscle to bones of the skeleton
Terrestrial Biome	A biome of or pertaining to land, as in terrestrial ecosystem
Testis (Plural, Testes)	One of two male reproductive organs that produces sperm and secretes testosterone
Testosterone	Male sex hormone secreted by the testes
Tetrapod	Vertebrate with four legs (amphibian, reptile, bird, or mammal)
Therapsid	Type of extinct organism that lived during the Permian Period and gave rise to mammals
Therian Mammal	Viviparous mammal that may be either a marsupial or placental mammal
Thylakoid Membrane	Membrane in a chloroplast where the light reactions of photosynthesis occur
Thyroid Gland	Large endocrine gland in the neck that secretes hormones that control the rate of cellular metabolism throughout the body
Tissue	Group of cells of the same kind that perform a particular function in an organism
Trachea	Long, tubular organ of the respiratory system, also called the wind pipe, that carries air between the larynx and lungs
Tracheophyte	Type of plant that has vascular tissues, such as a seed plant or flowering plant
Transcription	Process in which genetic instructions in DNA are copied to form a complementary strand of mrna
Transfer RNA (Trna)	Type of RNA that brings amino acids to ribosomes where they are joined together to form proteins
Transgenic Crop	Crop that has been genetically modified with new genes that code for traits useful to humans
Translation	Process in which genetic instructions in mrna are “read” to synthesize a protein
Transpiration	Process in which plants give off water vapor from photosynthesis through tiny pores, called stomata, in their leaves
Transport Protein	Protein in a plasma membrane that helps other substances cross the membrane
Trichomoniasis	Common sexually transmitted infection that is caused by protozoa
Trilobite	Oldest known arthropod, which is now extinct and known only from numerous fossils
Trophic Level	Feeding position in a food chain or food web, such as producer, primary consumer, or secondary consumer
Tropism	Turning by an organism or part of an organism toward or away from an environmental stimulus
Tumor	Abnormal mass of cells that may be cancerous
Tunicates	Members of the subphylum Urochordata are tunicates (also called sea squirts)
Unsaturated Fatty Acid	Molecule in lipids in which some carbon atoms are bonded to other groups of atoms rather than to hydrogen atoms
Ureter	Muscular, tube-like organ of the urinary system that moves urine by peristalsis from a kidney to the bladder
Urethra	Muscular, tube-like organ of the urinary system that carries urine out of the body from the bladder; in males, it also carries sperm out of the body
Urinary System	Organ system that includes the kidneys and is responsible for filtering waste products and excess water from the blood and excreting them from the body
Urination	Process in which urine leaves the body through a sphincter at the end of the urethra
Urine	Liquid waste product of the body that is formed by the kidneys and excreted by the other organs of the urinary system
Uterus (Plural, Uteri)	Female reproductive organ in therian mammals where an embryo or fetus grows and develops until birth
Vaccine	Substance containing modified pathogens that does not cause disease but provokes an immune response and results in immunity to the pathogen
Vacuole	Large saclike organelle that stores and transports materials inside a cell
Vagina	Female reproductive organ that receives sperm during sexual intercourse and provides a passageway for a baby to leave the mother’s body during birth
Vascular Tissue	Type of tissue in plants that transports fluids through the plant; includes xylem and phloem
Vector	Organism such as an insect that spreads pathogens from host to host
Vegetative Reproduction	Asexual reproduction in plants using nonreproductive tissues such as leaves, stems, or roots
Vein	Type of blood vessel that carries blood toward the heart from the lungs or body
Ventilation	Process of carrying air from the atmosphere into the lungs
Vertebrae (Singular, Vertebra)	Repeating bony units that make up the vertebral column of vertebrates
Vertebral Column	Bony support structure that runs down the back of a vertebrate animal; also called a backbone
Vertebrate	Animal with a vertebral column, or backbone
Vesicle	Small saclike organelle that stores and transports materials inside a cell
Vesicle Transport	Type of active transport in which substances are carried across the cell membrane by vesicles
Vestigial Structure	Structure such as the human tailbone or appendix that evolution has reduced in size because it is no longer used
Villi (Singular, Villus)	Microscopic, finger-like projections in the mucous membrane lining the small intestine that form a large surface area for the absorption of nutrients
Virion	Individual virus particle that consists of nucleic acid within a protein capsid
Virus	Tiny, nonliving particle that contains DNA but lacks other characteristics of living cells
Vitamin	Organic compound needed in small amounts for proper body functioning
Vivipary	Type of reproduction in which an embryo develops within, and is nourished by, the mother’s body
Vulva	External female reproductive structures, including the labia and vaginal opening
Water Cycle	Interconnected pathways through which water is recycled through the biotic and abiotic components of the biosphere
Water Mold	Fungus-like protist commonly found in moist soil and surface water
Weed	Plant that is growing where people do not want it
Wetland	Area that is saturated with water or covered by water for at least one season of the year
White Blood Cell	Type of cell in blood that defends the body against invading microorganisms or other threats in blood or extracellular fluid
Xerophyte	Plant that is adapted to a very dry environment
X-Linked Gene	Gene located on the X chromosome
X-Linked Trait	Trait controlled by a gene located on the X chromosome
Xylem	Type of vascular tissue in a plant that transports water and dissolved nutrients from roots to stems and leaves
Zooplankton	Tiny animals that feed on phytoplankton
Zygospore	Diploid spore in fungi that is produced by the fusion of two haploid parent cells
Zygote	Diploid cell that forms when two haploid gametes unite during fertilization