Spirogyra is an organism composed of cells, so it belongs to the level of organization known as a "cell." Spirogyra is a type of filamentous green algae that consists of many individual cells arranged in a long chain, held together by a gel-like substance. Although Spirogyra cells can perform some specialized functions, such as photosynthesis, they are not organized into tissues or organs. Therefore, Spirogyra is not classified as a "tissue" or "organ" level of organization. Finally, since Spirogyra is an individual organism and not part of a larger system, it is also not classified as a "system" level of organization.