The nucleus is the control center for the cell. All the other organelles depend on the nucleus to do its job so they can too. The nucleus is found in the center of the cell with a membrane around it. The membrane has pores on it so RNA can travel out and tell the organelles what to do. Also it keeps chromosomes protected within the membrane.
The nucleolus is found in the nucleus. It has no membrane around it, it is a dense region made of DNA, RNA and proteins. The nucleolus makes ribosomes in the nucleus. It is a very vital to a cells excistance.
The nuclear envelope is located outside the nucleus. It is a phospholipid bilayer with dozens of pores on it. This membrane controls what goes in and out of the nucleous. The envelope is vital to the nucleus because if anything could enter the nucleus it could cause harm to the cell.
Chromosomes & Chromatin
The Chromosomes and chromatin are both located in the nucleus. They are the double helix found in nucleotides. A chromatin is unwound DNA, chromosomes are tightly wound double helixes held together by proteins. They are both important because they both hold DNA that tells the cell and organelles what to do.
Ribosomes are small organelles that make protiens. They could be attatched to the Rough ER or free floating in the cytoplasm. They are non-membrane bound organelles with two sub-units. They are the smallest organelle found in cells. All organelles depend on Ribosomes to do their job. Ribosomes help make proteins on the Rough Endoplasmic Reticulum.
The cell membrane is surrounding an animal cell or just inside the cell wall in plant cells. It is made of a bilayer of phospholipids. The cell membrane controls what gets in and out of a cell, it also allow a cell to have a different chemical environment then outside the cell. The cell membrane may be the second most important organelle just behind the nucleus.