Term | Definition |
periods | eras are subdivided into periods |
epochs | periods are subdivided into epochs |
mass extinction | the extinction of many species on Earth within a short period of time |
land bridge | connects two continents that were previously separated |
eons | the longest unit of geological time |
eras | eons are subdivided into eras |
geographic isolation | the separation of a population of organisms from the rest of its species |
cell theory | all living things are made of one or more cells, the cell is the smallest unit of life, and all new cells come from preexisting cells |
macromolecules | form by joining many small molecules together |
nucleic acids | macromolecules that form when long chains of molecules called nucleotides join tofether |
proteins | long chains of amino acid molecules |
lipid | large macromolecule that dose not dissolve in water |
carbohydrates | one sugar molecule, two sugar molecules, or a long chain of sugar molecules |
cell membrane | flexible covering that protects the inside of the cell from the environment outside the cell |
cell wall | stiff structure outside the cell membrane |
cytoplasm | fluid inside the cell that contains salts and other molecules |
cytoskeleton | a network of threadlike proteins that are joined together |
organells | specialized functions |
nucleus | part of a eukrayotic cell that directs cell activities and contains genetic information stored in DNA |
chloroplasts | are membrane-bound organelles that use light energy and make food--a sugar called gluecose--form water and carbon dioxide in a process known as photosynthesis |