About Cells
The nucleus contains the entire DNA instruction manual for everything a cell needs to do: take in nutrients, process them into energy, grow, and even when and how to die.
So many instructions make the DNA manual very big and bulky. Like a set of encyclopedias at the library, it stays in one place. Pages can be copied out of it as needed and taken out into the rest of the cell - the cytoplasm.
For a long time we thought that the cytoplasm was nothing but fluid inside the bag of the cell membrane, but now we know that it has its own structure. The machinery you'll see in the cytoplasm is fixed in place by scaffolding called the cytoskeleton.
A good college-level introduction
to cell biology