| Term | Definition |
|---|
| skepticism | a habit of mind in which a person questions the validity of accepted ideas |
| observation | a system of ideas that explains many related observations and is supported by a large body of evidence acquired through scientific investigation |
| hypothesis | a testable idea or explanation that leads to scientific investigation |
| experiment | a procedure that is carried out under controlled conditions to discover demonstrate, or test a fact, theory, or general truth |
| control group | in an experiment, a group that serves as a standard of comparison with another group to which the control group is identical except for one factor |
| theory | a system of ideas that explains many related observations and is supported by a large body of evidence acquired through scientific investigation |
| SI | Le Système International d'Unités, or the International System of Units, which is the measurement system that is accepted worldwide |
| biology | the scientific study of living organisms and their interactions with the environment |
| cell | in biology, the smallest unit that can perform all life processes; cells are covered by a membrane and contain DNA and cytoplasm |
| homeostasis | the maintenance of a constant internal state in a changing environment; a constant internal state that is maintained in a changing environment by continually making adjustments to the internal and external environment |
| metabolism | the sum of all chemical processes that occur in an organism |
| reproduction | the process of producing offspring |
| heredity | the passing of genetic traits from parent to offspring |
| evolution | generally, in biology, the process of change by which new species develop from preexisting species over time; at the genetic level, the process in which inherited characteristics within populations change over time; the process defined by Darwin as "descent with modification" |
| epidemiology | the study of the distribution of diseases in populations and the study of factors that influence the occurrence and spread of disease |
| vaccination | the administration of treated microorganisms into humans or animals to induce an immune response |
| genetics | the science of heredity and of the mechanisms by which traits are passed from parents to offspring |
| genome | the complete genetic material contained in an individual or species |
| genetic engineering | a technology in which the genome of a living cell is modified for medical or industrial use |
| biometrics | the statistical analysis of biological data; especially the measurement and analysis of unique physical or behavioral characteristics to verify the identity of a person |
| ecology | the study of the interactions of living organisms with one another and with their environment |
| enviornmental science | the study of the air, water, and land surrounding an organism or a community, which ranges from a small area to Earth's entire biosphere; it includes the study of the impact of humans on the environment |
| atom | the smallest unit of an element that maintains the chemical properties of that element |
| element | a substance that cannot be separated or broken down into simpler substances by chemical means; all atoms of an element have the same atomic number |
| valence electron | an electron that is found in the outermost shell of an atom and that determines the atom's chemical properties |
| compound | a substance made up of atoms of two or more different elements joined by chemical bonds |
| molecule | a group of atoms that are held together by chemical forces; a molecule is the smallest unit of matter that can exist by itself and retain all of a substance's chemical properties |
| ion | an atom, radical, or molecule that has gained or lost one or more electrons and has a negative or positive charge |
| cohesion | the force that holds molecules of a single material together |
| adhesion | the attractive force between two bodies of different substances that are incontact with each other |
| solution | a homogeneous mixture throughout which two or more substances are uniformly dispersed |
| acid | any compound that increases the number of hydronium ions when dissolved in water; acids turn blue litmus paper red and react with bases and some metals to form salts |
| base | any compound that increases the number of hydroxide ions when dissolved in water; bases turn red litmus paper blue and react with acids to form salts |
| pH | a value that is used to express the acidity or alkalinity (basicity) of a system; each whole number on the scale indicates a tenfold change in acidity; a pH of 7 is neutral, a pH of less than 7 is acidic, and a pH of greater than 7 is basic |
| buffer | a solution made from a weak acid and its conjugate base that neutralizes small amounts of acids or bases added to it |
| carbohydrate | a class of molecules that includes sugars, starches, and fiber; contains carbon, hydrogen, and oxygen |
| lipid | a fat molecule or a molecule that has similar properties; examples include oils, waxes, and steroids |
| protein | an organic compound that is made of one or more chains of amino acids and that is a principal component of all cells |
| amino acid | a compound of a class of simple organic compounds that contain a carboxyl group and an amino group and that combine to form proteins |
| nucleic acid | an organic compound, either RNA or DNA, whose molecules are made up of one or two chains of nucleotides and carry genetic information |
| nucleotide | an organic compound that consists of a sugar, a phosphate, and a nitrogenous base; the basic building block of a nucleic-acid chain |
| DNA | deoxyribonucleic acid, the material that contains the information that determines inherited characteristics |
| RNA | ribonucleic acid, a natural polymer that is present in all living cells and that plays a role in protein synthesis |
| ATP | adenosine triphosphate, an organic molecule that acts as the main energy source for cell processes; composed of a nitrogenous base, a sugar, and three phosphate groups |
| energy | the capacity to do work |
| reactant | a substance or molecule that participates in a chemical reaction |
| product | a substance that forms in a chemical reaction |
| activation energy | the minimum amount of energy required to start a chemical reaction |
| enzyme | a molecule, either protein or RNA, that acts as a catalyst in biochemical reactions |
| active site | on an enzyme, the site that attaches to a substrate |
| subtrate | a part, substance, or element, that lies beneath and supports another part, substance or element; reactions catalyzed by enzymes. |
| cell membrane | a phospholipid layer that covers a cell s surface and acts as a barrier between the inside of a cell and the cell's environment |
| cytoplasm | the region of the cell within the membrane that includes the fluid, the cytoskeleton, and all of the organelles except the nucleus |
| ribosome | a cell organelle composed of RNA and protein; the site of protein synthesis |
| prokaryote | a single-celled organism that does not have a nucleus or membranebound organelles; examples are archaea and bacteria |
| eukaryote | an organism made up of cells that have a nucleus enclosed by a membrane, multiple chromosomes, and a mitotic cycle; eukaryotes include protists, animals, plants, and fungi but not archaea or bacteria |
| nucleus | in a eukaryotic cell, a membranebound organelle that contains the cell's DNA and that has a role in processes such as growth, metabolism, and reproduction |
| organelle | one of the small bodies that are found in the cytoplasm of a cell and that are specialized to perform a specific function |
| vesicle | a small cavity or sac that contains materials in a eukaryotic cell; forms when part of the cell membrane surrounds the materials to be taken into the cell or transported within the cell |
| endoplasmic reticulum | a system of membranes that is found in a cell's cytoplasm and that assists in the production, processing, and transport of proteins and in the production of lipids |
| Golgi apparatus | a cell organelle that helps make and package materials to be transported out of the cell |
| vacuole | a fluid-filled vesicle found in the cytoplasm of plant cells or protozoans |
| chloroplast | an organelle found in plant and algae cells where photosynthesis occurs |
| mitochondrion | in eukaryotic cells, the cell organelle that is surrounded by two membranes and that is the site of cellular respiration, which produces ATP |
| flagellum | a long, hairlike structure that grows out of a cell and enables the cell to move |
| tissue | a group of similar cells that perform a common function |
| organ | a collection of tissues that carry out a specialized function of the body |
| organ system | a group of organs that work together to perform body functions |
| colonial organsim | a collection of genetically identical cells that are permanently associated but in which little or no integration of cell activities occurs |
| phospholipid | a lipid that contains phosphorus and that is a structural component in cell membranes |
| lipid bilayer | the basic structure of a biological membrane, composed of two layers of phospholipids |
| equilibrium | in biology, a state that exists when the concentration of a substance is the same throughout a space |
| concentration gradient | a difference in the concentration of a substance across a distance |
| diffusion | the movement of particles from regions of higher density to regions of lower density |
| carrier protein | a protein that transports substances across a cell membrane |
| osmosis | the diffusion of water or another solvent from a more dilute solution (of a solute) to a more concentrated solution (of the solute) through a membrane that is permeable to the solvent |
| sodium-potassium pump | a carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell |
| signal | anything that serves to direct, guide, or warn |
| receptor protein | a protein that binds specific signal molecules, which causes the cell to respond |
| second messenger | a molecule that is generated when a specific substance attaches to a receptor on the outside of a cell membrane, which produces a change in cellular function |
| photosynthesis | the process by which plants, algae, and some bacteria use sunlight, carbon dioxide, and water to produce carbohydrates and oxygen |
| cellular respiration | the process by which cells produce energy from carbohydrates; atmospheric oxygen combines with glucose to form water and carbon dioxide |
| ATP synthase | an enzyme that catalyzes the synthesis of ATP |
| electron transport chain | a series of molecules, found in the inner membranes of mitochondria and chloroplasts, through which electrons pass in a process that causes protons that causes protons to build up on one side of the membrane |
| thylakoid | a membrane system found within chloroplasts that contains the components for photosynthesis |
| pigment | a substance that gives another substance or a mixture its color |
| chlorophyll | a green pigment that is present in most plant and algae cells and some bacteria, that gives plants their characteristic green color, and that absorbs light to provide energy for photosynthesis |
| Calvin cycle | a biochemical pathway of photosynthesis in which carbon dioxide is converted into glucose using ATP |
| glycolysis | the anaerobic breakdown of glucose pyruvic acid, which makes a small amount of energy available to cells in the form of ATP |
| anaerobic | describes a process that does not require oxygen |
| aerobic | describes a process that requires oxygen |
| Krebs cycle | a series of biochemical reactions that convert pyruvic acid into carbon dioxide and water; it is the major pathway of oxidation in animal, bacterial, and plant cells, and it releases energy |
| fermentation | the breakdown of carbohydrates by enzymes, bacteria, yeasts, or mold in the absence of oxygen |
| gene | the most basic physical unit of heredity; a segment of nucleic acids that codes for a functional unit of RNA and/or a protein |
| chromosome | in a eukaryotic cell, one of the structures in the nucleus that are made up of DNA and protein; in a prokaryotic cell, the main ring of DNA |
| chromatin | the substance that composes eukaryotic chromosomes; it consists of specific proteins, DNA, and small amounts of RNA |
| histone | a type of protein molecule found in the chromosomes of eukaryotic cells but not prokaryotic cells |
| nucleosome | a eukaryotic structural unit of chromatin that consists of DNA wound around a core of histone proteins |
| chromatid | one of the two strands of a chromosome that become visible during meiosis or mitosis |
| centromere | the region of the chromosome that holds the two sister chromatidstogether during mitosis |
| cell cycle | the life cycle of a cell; in eukaryotes, it consists of a cell-growth period in which DNA is synthesized and a cell-division period in which mitosis takes place |
| interphase | the period of the cell cycle during which activities such as cell growth and protein synthesis occur without visible signs of cell division |
| mitosis | in eukaryotic cells, a process of cell division that forms two new nuclei, each of which has the same number of chromosomes |
| cytokinesis | the division of the cytoplasm of a cell; it follows the division of the cell |
| spindle | a network of microtubules that forms during mitosis and moves chromatids to the poles |
| centrosome | an organelle that contains the centrioles and is the center of dynamic activity in mitosis |
| cancer | a type of disorder of cell growth that results in invasion and destruction of surrounding healthy tissue by abnormal cells |
| tumor | a growth that arises from normal tissue but that grows abnormally in rate and structure and lacks a function |
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