Traditionally, a microscope.
But if you consider a more complex application of the sciences, such as Biochemistry or Cellular Genetics, then the answer to this question becomes far too complex.
Because cells are way to small to see without a microscope.
A cell biologist-
It is illegal to use humans. Rats and mice are inexpensive and easy to keep.
Scientists such as biologists, microbiologists, and material scientists use microscopes to study small organisms, cells, tissues, and materials at a microscopic level. Microscopes help these scientists observe and analyze the intricate structures and functions of their subjects.
to study dolphins
Scientists use microscopes to look at cells. There are different types of microscopes, such as light microscopes and electron microscopes, that allow scientists to observe cells at various levels of detail. These instruments magnify the structures within cells, enabling researchers to study their composition and functions.
a cytologist cyto- cell
Scientists use mainly fossils.
Microscopes allow scientists to magnify the image of cells, making them visible to the human eye. This enables scientists to observe cell structures, functions, and interactions in detail, aiding in the study of their biology and behavior.
Cell biologists or sometimes cytologists.
whattools do scientist use to study meteors
Scientists use an electron accelerator :)