There are many parts of a cell, most of them are organelles, but three of them are mitochondria, lysosomes, and ribosomes. Mitochondria are covered in two membranes and break down nutrients to produce energy. Without energy, the cell wouldn't be able to perform its activities and would starve to death. Lysosomes act as the garbage-disposal of the cell and recycle waste, broken or injured cell parts, and other useless material. Lysosomes clear the space in a cell, without them, the cell would explode from a buildup of waste. Ribosomes are scattered throughout the cell, found in cytoplasm and on the rough ER. Ribosomes are not covered in a membrane, but create proteins that are necessary for almost every cell activity. The nucleolus makes ribosomes.
Those were some organelles, but there are other parts of the cell, too. For example, the cell membrane is found in all cells, and controls what comes in or goes out of the cell. Without the cell membrane, the cell would have no protection or separation from its outside environment, and would not be able to ho