adaptation In evolutionary biology, a particular structure, physiological process, or behavior that makes an organism better able to survive and reproduce. Also, the evolutionary process that leads to the development or persistence of such a trait.
archaeans Unicellular organisms lacking a nucleus and lacking peptidoglycan in the cell wall. Once grouped with the bacteria, archaeans possess distinctive membrane lipids.
bacteria Unicellular organisms lacking a nucleus, possessing distinctive ribosomes and initiator tRNA, and generally containing peptidoglycan in the cell wall. Different bacterial groups are distinguished primarily on nucleotide sequence data.
comparative method An experimental design in which two samples or populations exposed to different conditions or treatments are compared to each other.
controlled experiment An experimental design in which a sample or population is divided into two groups; one group is exposed to a manipulated variable while the other group serves as a nontreated control. The two groups are compared to see if there are changes in a “dependent” variable as a result of the experimental manipulation.
DNA (deoxyribonucleic acid) The fundamental hereditary material of all living organisms. In eukaryotes, stored primarily in the cell nucleus. A nucleic acid using deoxyribose rather than ribose.
eukaryotes Organisms made up of one or more complex cells in which the genetic material is contained in nuclei.
evolution Any gradual change. Organic or Darwinian evolution, often referred to as evolution, is any genetic and resulting phenotypic change in organisms from generation to generation.
experiment A testing process to support or disprove hypotheses and to answer questions. The basis of the scientific method.
genome All the genes in a complete haploid set of chromosomes.
hypothesis A tentative answer to a question, from which testable predictions can be generated.
metabolism The sum total of the chemical reactions that occur in an organism, or some subset of that total (as in respiratory metabolism).
natural selection The differential contribution of offspring to the next generation by various genetic types belonging to the same population. The mechanism of evolution proposed by Charles Darwin.
nucleotide The basic chemical unit in a nucleic acid. A nucleotide in RNA consists of one of four nitrogenous bases linked to ribose, which in turn is linked to phosphate. In DNA, deoxyribose is present instead of ribose.
null hypothesis The assertion that an effect proposed by its companion hypothesis does not in fact exist.
organelles Organized structures found in or on eukaryotic cells. Examples include ribosomes, nuclei, mitochrondria, chloroplasts, cilia, and contractile vacuoles.
photosynthesis Metabolic processes, carried out by green plants, by which visible light is trapped and the energy used to synthesize compounds such as ATP and glucose.
Prokaryotes Organisms whose genetic material is not contained within a nucleus: the bacteria and archaea. Considered an earlier stage in the evolution of life than the eukaryotes.
protein One of the most fundamental building substances of living organisms. A long-chain polymer of amino acids with twenty different common side chains. Occurs with its polymer chain extended in fibrous proteins, or coiled into a compact macromolecule in enzymes and other globular proteins.
scientific method A means of gaining knowledge about the natural world by making observations, posing hypotheses, and conducting experiments to test those hypotheses.
species The basic lower unit of classification, consisting of an ancestor–descendant lineage of populations of closely related and similar organisms. The more narrowly defined “biological species” consists of individuals capable of interbreeding freely with each other but not with members of other species.