All living things are made of cells, which are the basic units of life. There are two main types of cells - prokaryotic and eukaryotic. Prokaryotic cells do not have membrane-bound organelles or nuclei, while eukaryotic cells do. Organelles such as the nucleus, mitochondria, endoplasmic reticulum, Golgi complex, lysosomes, vacuoles, chloroplasts and cell walls enable cells to carry out functions necessary for life like metabolism, transport, and waste removal. The document provides descriptions of these key cellular structures.