biology definitions nucleus
By Regina Bailey. Definition: The nucleus is a membrane bound structure that contains the cell's hereditary information and controls the cell's growth and reproduction.It is commonly the most prominent organelle in the cell.The nucleus is surrounded by a structure called the nuclear envelope.This membrane separates the contents of the nucleus from the cytoplasm. The cell's chromosomes are also housed within the nucleus.he nucleus is surrounded by a structure called the nuclear envelope. This membrane separates the contents of the nucleus from the cytoplasm. The cell's chromosomes are also housed within the nucleus.