The nucleus is the center of the cell. The nucleus holds most of the genetic material that the cell requires to function. The nucleus is basically mthe architect for what and when things happen in the cell. Here are some websites to look at for more info:
http://www.biology-online.org/dictionary/Nucleus
http://micro.magnet.fsu.edu/cells/nucleus/nucleus.html
http://www.biology-online.org/dictionary/Nucleus
http://micro.magnet.fsu.edu/cells/nucleus/nucleus.html