1. Plasma membrane - also known as cell membrane. It is 'the skin of a cell', which acts as a physically controlling barrier for the entrance and exit of materials. It's made up of proteins and lipids.
2. Cytoplasm - everything inside the cell (but not including the nucleus). Much of the cytoplasm is a transparent and gel-like material known as cytosol; cell structures are suspended in it.
3. Ribosomes - these are organelles that are in charge of making proteins.
4. DNA - Molecules containing the genetic code of a cell, which tells the cell what to do. It is located in the nucleus for eukaryotic cells; for prokaryotic cells, it is located in a part of the cell called the nucleoid.