cell The smallest structural unit of an organism that is capable of independent functioning.
gene A hereditary unit consisting of a sequence of DNA that occupies a specific location on a chromosome and determines a particular characteristic in an organism.
genetic mutation A change in the DNA of a gene.
biological evolution The process of physical change in living things across generations.
blue-green bacteria Microorganisms that live in the water and make their own food through photosynthesis. Also called cyanobacteria or blue-green algae, these organisms help turn carbon dioxide to oxygen in the atmosphere. They are also the oldest known fossils.
photosynthesis The process in green plants and certain other organisms by which sugars are created from carbon dioxide and water using light as an energy source.
phycology The study of algae.
phylogeny The historical relationships among lineages or organisms or their parts, such as their genes.See the National Library of Medicine website .