In sociology and psychology, some definitions include only consciously malignant forms of discrimination. Some definitions of racism also include discriminatory behaviors and beliefs based on cultural, national, ethnic, caste, or religious stereotypes.
A cell is much, much larger than an atom. A typical animal cell might be 10,000 times as wide, long, and tall as a typical atom, or about 1 trillion times the volume of an atom. Another way to arrive at this answer is to consider the fact that cells are made up of atoms, so the atoms must therefore be smaller.
A proton is a tiny particle, smaller than an atom. Protons are too small to see, even with an electron microscope, but we know they must be there because that's the only way we can explain how atoms behave. To give you an idea how small a proton is, if an atom was the size of a football stadium, then a proton would still be smaller than a marble.