Anton van Leeuwenhoek is a scientist who saw cells soon after Hooke did. He made use of a microscope containing improved lenses that could magnify objects almost 30ox. Under these microscopes, Leeuwenhoek found moving objects that he named “animalcules,” which included protozoa and other unicellular organisms, like bacteria. He was also able to observe red blood cells and sperm cells. To which of the tenets of the Cell Theory did Leeuwenhoek make the biggest contribution?