| A | B |
|---|
| absolute dating | a technique used to determine the actual age of a fossil |
| active transport | the movement of materials through a cell membrane using energy |
| adaptation | a trait that helps an organism survive and reproduce |
| alleles | the different forms of a gene |
| amino acids | small molecules that are linked together chemically to form proteins |
| amniocentesis | a technique by which a small amount of the fluid that surrounds a developing baby is removed; the fluid is analyzed to determine whether the baby will have a genetic disorder |
| atom | the smallest unit of an element |
| autotroph | an organism that makes its own food |
| branching tree | a diagram that shows how scientists think different groups of organisms are related |
| cancer | a disease in which some body cells grow and divide uncontrollably, damaging the parts of the body around them |
| carbohydrates | energy-rich organic compounds, such as sugars and starches, that are made of the elements carbon, hydrogen, and oxygen |
| carrier | a person who has one recessive allele for a trait and one dominant allele, but does not have the trait |
| cast | a type of fossil that forms when a mold becomes filled in with minerals that then harden |
| cell | the basic unit of structure and function in living things |
| cell cycle | the regular sequence of growth and division that cells undergo |
| cell membrane | a cell structure that controls which substances can enter or leave the cell |
| cell theory | a widely accepted explanation of the relationship between cells and living things |
| cell wall | a rigid layer of nonliving material that surrounds the cells of plants and some other organisms |
| chemotherapy | the use of drugs to kill cancer cells |
| chlorophyll | a green pigment found in the choloroplasts of plants, algae, and some bacteria |
| chloroplast | a structure in the cells of plants and some other organisms that captures energy from sunlight and uses it to produce food |
| chromatid | one of the identical rods of a chromosome |
| chromatin | material in cells that contains DNA and carries genetic information |
| chromosome | a doubled rod of condensed chromatin; contains DNA that carries genetic information |
| clone | an organism that is genetically identical to the organism from which it was produced |
| codominance | a condition in which neither of the two alleles of a gene is dominant or recessive |
| compound | two or more elements that are chemically combined |
| compound microscope | a light microscope that has more than one lens |
| controlled experiment | an experiment in which all factors except one are kept constant |
| convex lens | a curved lens in which the center is thicker than the edges |
| cytokinesis | the final stage of the cell cycle, in which the cell's cytoplasm divides, distributing the organelles into each of the two new cells |
| cytoplasm | the region between the cell membrane and the nucleus; in organisms without a nucleus, the region located inside the cell membrane |
| diffusion | the process by which molecules move from an area of high concentration to an area of lower concentration |
| DNA | Deoxyribonucleic acid; the genetic material that carries information about an organism and is passed from parent to offspring |
| dominant allele | an allele whose trait always shows up in the organism when the allele is present |
| element | any substance that cannot be broken down into simpler substances |
| endoplasmic reticulum | a cell structure that forms a maze of passageways in which proteins and other materials are carreid from one part of the cell to another |
| enzyme | a type of protein that speeds up a chemical reaction in a living thing |
| evolution | the gradual change in a species over time |
| extinct | a species that does not have any living members |
| fermentation | the process by which cells break dwon molecules to release energy without using oxygen |
| fossil | the preserved remains or traces of an organism that lived in the past |
| fossil record | the millions of fossils that scientists have collected |
| gene therapy | the insertation of working copies of a gene into the cells of a person with a genetic disorder in an attempt to correct the disorder |
| gene | a segment of DNA on a chromosome that codes for a specific trait |
| genetic disorder | an abnormal condition that a person inherits through genes or chromosomes |
| genetic engineering | the transfer of a gene from the DNA of one organism into another organism, in order to produce an organism with desired traits |
| genetics | the scientfic study of heredity |
| genome | all of the DNA in one cell of an organism |
| genotype | an organism's genetic makeup, or allele combinations |
| Golgi body | a structure in a cell that receives proteins and other newly formed materials from the endoplasmic reticulum, packages them, and distributes them to other parts of the cell |
| gradualism | the theory that evolution occurs slowly but steadily |
| half-life | the time it takes for half of the atoms in a radioactive element to break down |
| heredity | the passing of traits from parents to offspring |
| heterotroph | an organism that cannot make its own food |
| heterozygous | having two different alleles for a trait |
| homologous structures | body parts that are structurally similar in related species; provide evidence that the structures were inherited from a common ancestor |
| homozygous | having two identical alleles for a trait |
| hybrid | an organism that has two different alleles for a trait; an organism that is heterozygous for a particular trait |
| hybridization | a selective breeding method in which two geneticaly different individuals are crossed |
| hypothesis | a prediction about the outcome of an experiment |
| inbreeding | a selective breeding method in which two individuals with identical or similar sets of alleles are crossed |
| inorganic compound | a compound that does not contain carbon |
| interphase | the stage of the cell cycle that takes place before cell division occurs; during this stage, the cell grows, copies its DNA, and prepares to divide |
| karyotype | a picture of all the chromosomes in a cell arranged in pairs |
| lipids | energy-rich organic compounds, such as fats, oils, and waxes, that are made of carbon, hydrogen, and oxygen |
| lysosome | a small round cell structure that contains chemicals that break down large food particles into smaller ones |
| magnification | the ability to make things look larger than they are |
| manipulated variable | the one factor that a scientist changes during an experiment |
| meiosis | the process that occurs in sex cells (sperm and egg) by which the number of chromosomes is reduced by half |
| messenger RNA | RNA that copies the coded message from DNA in the nucleus and carries the message into the cytoplasm |
| microscope | an instrument that makes small objects look larger |
| mitochrondria | rod-shaped cell structures that produce most of the energy needed to carry out the cell's functions |
| mitosis | the stage of the cell cycle during which the cell's nucleus divides into two new nuclei and one copy of the DNA is distributed into each daughter cell |
| mold | a type of fossil formed when a shell or other hard part of an organism dissolves, leaving an empty space in the shape of the part |
| molecule | the smallest unit of most compounds |
| multiple alleles | three or more forms of a gene that code for a single trait |
| mutation | a change in a gene or chromosome |
| natural selection | the process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species |
| nucleic acid | a very large organic molecule made of carbon, oxygen, hydrogen, nitrogen, and phosphorus, that contains instructions that cells need to carry out all the functions of life |
| nucleus | a cell structure that contains nucleic acids, the chemical instructions that direct all the cell's activities |
| operational definition | a statement that describes how a particular variable is to be measured or a term is to be defined |
| organelle | a tiny cell structure that carries out a specific function within the cell |
| organic compound | a compound that contains carbon |
| osmosis | the diffusion of water molecules through a selectively permeable membrane |
| passive transport | the movement of materials through a cell membrane without using energy |
| pedigree | a chart of "family tree" that tracks which members of a family have a particular trait |
| petrified fossil | a fossil formed when minerals replace all or part of an organism |
| phenotype | an organism's physical appearance, or visible traits |
| photosynthesis | the process by which plants and some other organisms capture the energy in sunlight and use it to make food |
| pigment | a colored chemical compound that absorbs light |
| probability | the likelihood that a particular even will occur |
| proteins | large organic molecules made of carbon, hydrogren, oxygen, nitrogen, and sometimes sulfur |
| punctuated equilibria | the theory that species evolve during short periods of rapid change |
| Punnett square | a chart that shows all the possible combinations of alleles that can result from a genetic cross |
| purebred | an organism that always produces offspring with the same form of a trait as the parent |
| radioactive element | an unstable particle that breaks down into a different element |
| recessive allele | an allele that is masked when a dominant allele is present |
| relative dating | a technique used to determine which of two fossils is older |
| replication | the process by which a cell makes a copy of the DNA in its nucleus |
| resolution | the ability to clearly distinguish the individual parts of an object |
| respiration | the process by which cells break down simple food molecules to release the energy they contain |
| responding variable | the factor that changes as a result of changes to the manipulated variable in an experiment |
| ribosome | a small grain-like structure in the cytoplasm of a cell where proteins are made |
| RNA | Ribonucleic acid; a nucleic acid that plays an important role in the production of proteins |
| scientific theory | a well-tested concept that explains a wide range of observations |
| sedimentary rock | rock formed when layers of sediments harden over millions of years |
| selective breeding | the process of selecting a few organisms with desired traits to serve as parents of the next generation |
| selectively permeable | a property of cell membranes that allows some substances to pass through, while others cannot |
| sex-linked gene | a gene that is carried on the X or Y chromosome |
| species | a group of similar organisms that can mate with each other and produce fertile offspring |
| stomata | small openings on the underside of a leaf through which oxygen and carbon dioxide can move |
| trait | a characteristic that an organism can pass on to its offspring through its genes |
| transfer RNA | RNA in the cytoplasm that carries an amino acid to the ribomsome and adds it to the growing protein chain |
| tumor | a mass of abnormal cells that develops when cancerous cells divide and grow uncontrollably |
| vacuole | a water-filled sac inside a cell that acts as a storage area |
| variable | any factor that can change in an experiment |
| variation | any difference between individuals of the same species |
