The Cell The cell is one of the most important concepts in biology since every living organism is made of cells. Bacteria are single celled while you are made up of trillions of cells. As different as we are from bacteria, our cells share some important similarities. All cells have a cell membrane that separates them from the outside environment and all cells have ribosomes where proteins are made. Attribution-Noncommercial 3.0 United States, more free study guides at www.Biology101.org, copyright Anthony D'Onofrio a quick overview The basic diagram of the cell shown above represents most eukaryotic cells (humans, plants, fungi). One main distinction is that plants have a cell wall outside the cell membrane that animal cells lack.