Answer:
Both cellular structures and cellular processes.
Step-by-step explanation:
Magnifying lenses have been around since approximately 1000 AD. By 1590, the first simple microscope was created. Less than 100 years later, Robert Hooke used this new technology to suggest that substances are composed of cells. His drawings show how microscopes can be used to examine cell structure.
Microscopes continued to develop over time. In 1931, the electron microscope was invented, so cellular organelles could be viewed in greater detail. Now, as demonstrated by the second image, it is possible to not only see cellular structures, but also cellular processes, such as mitosis.