A nucleus represents different things depending on the area of science being studied. In general, the nucleus is the center of an object and its most important part.
The nucleus exists in the fields of biology and physics. In biology, the nucleus represents the center of the cell, enclosed by a membrane, where DNA and genetic material is contained. In physics, the nucleus is the center of an atom containing protons and neutrons. A cell's nucleus is made of nucleoplasm and a nucleoprotein-rich network. Nucleus represents different things in chemistry, astronomy, meteorology, botany, and anatomy. For example, in astronomy, the nucleus refers to the center of the head of a comet or the brightest part of a nebula or galaxy.