The Fundamental Units of Life Hierarchy of biological organization ? cells at bottom Plants & animals are multicellular (eukaryotic) Cells sense and respond to environmental fluctuations Keep biological theme in mind : evolution ? all cells can be seen as the descent of earlier cells that have been modified during evolution on Earth 6.1 To study cells, biologists use microscopes and tools of biochemistry Invention of microscopes in 1590 and refinement in 1600s Light Microscopes ? visible light is passed through the specimen then the glass lenses -First used by Renaissance scientists and the one used in the lab -Lenses refract light so image of specimen has been magnified Three important parameter in microscopy ? Magnification, Contrast, & Resolution