Cells are the basic unit of structure and form in all living things. Some organisms are made of only one cell while others are made of trillions . Each cell must be able to carry out the basic functions of life, including obtaining and using nutrients, producing proteins, shipping proteins, etc. Some cells like prokaryotes are relatively simple with very few internal structures. Larger and more complex cells like eukaryotes require specialized structures to accomplish all of the necessities of life. These structures are called organelles, and they include the nucleus, Golgi apparatus, endoplasmic reticulum, vacuoles, mitochondria, and more.