The nucleus is a critical part of a living cell – be it a plant cell or an animal cell. The nucleus is considered the central part of the cell, and has a number of functions, mostly related to the genetic make up. It contains the genetic data, and transfers this data on to the daughter cells as a result of the process of mitosis. The nucleus is made of a number of components, one of which is the nucleolus. The nucleolus contains Ribo Nucleic Acid or RNA and is a critical component of the nucleus.
At a certain level of magnification under a microscope, one can see the nucleus, and at a higher degree of magnification, one can make out the nucleolus. However, it is wrong to say that the nucleolus is a nucleus within a nucleus; it is just a component of the nucleus, albeit a vital one. On higher magnification, one can view the components of the nucleolus, but you would not get to see another nucleus inside it, simply because there is no nucleus inside a nucleolus.
At a certain level of magnification under a microscope, one can see the nucleus, and at a higher degree of magnification, one can make out the nucleolus. However, it is wrong to say that the nucleolus is a nucleus within a nucleus; it is just a component of the nucleus, albeit a vital one. On higher magnification, one can view the components of the nucleolus, but you would not get to see another nucleus inside it, simply because there is no nucleus inside a nucleolus.