Human cells feature a cell membrane surrounding two compartments: the cytoplasm and the nucleus of the cell. Each cell also has several organelles, or structures with specific functions.
Cytoplasm, a gel-like substance composed of fluid and cell organelles, cushions the organelles and protects them from damage. The nucleus contains genetic material that controls the activities of each cell. Surrounding the nucleus is a nuclear membrane that allows certain materials to pass into and out of the nucleus.
Human cells also feature organelles called ribosomes, mitochondria, lysosomes and endoplasmic reticulum. Ribosomes produce the proteins each cell needs to function properly. Some ribosomes are attached to the endoplasmic reticulum, while others are free to move about the cell. Mitochondria help cells produce energy by breaking down sugars. Each mitochondrion is bean-shaped and has a network of inner membranes.
Lysosomes contain the enzymes used to digest large molecules and remove old parts from the cell. If there is no food available in the cell, the lysosomes actually use the cell organelles as a source of nutrients. The endoplasmic reticulum manufactures and packages substances for transport throughout the cell. Endoplasmic reticulum is made up of a network of membranes connected to the nucleus.
The Golgi complex, which is made up of layers of membranes, is another packaging organelle found within human cells. After combining simple molecules into complex ones, the Golgi complex packages the large molecules as vesicles.