The plasma membrane acts as a borderline which controls the exchange of substances with the outside of the cell.
The nucleus is the control center of the cell and contains the genetic information in form of chromosomes.
The endoplasmic reticulum is connected to the nucleus and is the site where numerous substances are formed, stocked and relayed. This structure is in touch with other membranes, either directly or indirectly by using vesicles – small spherical compartments used for transporting cellular products. This allows it to direct critical substances to the areas they are needed.
Ribosomes are complex molecular machines which translate the genetic information into functional units (proteins). These small structures do not possess any membrane and are 15-30 nanometers in size.
Mitochondria are the cellular power plants of the cell and convert energy obtained by sugar into cellular energy. This process is known as cellular respiration.
The Golgi apparatus is responsible sorting, packaging, modifying and distributing cellular products. Packaged proteins are either transported within the cell or released (exocytosis, e. g. insulin).
Lysosomes are digestive vesicles which act as the wastepaper baskets of the cell. Cellular substances are degraded or recycled within these structures.