Viruses a) have large central nuclei b) vary greatly in size and structure. c) rarely contain dna or rna. d) can be seen with a basic compound light microscope.

they float because they are less dense than the water itself

something denser than water, like a rock, will sink to the bottom

thrombocytopenia, which is a deficiency in blood platelets, can cause bleeding and bruising in the dermis similar to senile purpura. other possible causes include: exposure to ultraviolet rays and aging skin are common causes of senile purpura. senile purpura may also be a sign of collagen loss in the skin and bones.