What is a "Nucleus"?
1) the structure that forms the surface of a cell separating its contents from the outside world
2) an organelle of some eukaryotic cells in which photosynthesis occurs, using the energy of light to make organic compounds from carbon dioxide and water
3) a cell organelle that is essential to cell functions including reproduction, contains the cell's chromosomes, and is enclosed by a membrane
4) membrane-bound organelles in eukaryotic cells in which cellular respiration takes place, using oxygen to break down glucose to carbon dioxide and water and putting the energy into a more readily usable form in ATP molecule
