An animal cell is defined as a eukaryotic cell in which all the organelles are contained in membranes. Organelles included in an animal cell are a nucleus, the centrioles, an endoplasmic reticulum, a golgi complex, lysosomes, the mitochondria and ribosomes.
The outer membrane of an animal cell, or cell membrane, is semi-permeable and allows essential nutrients into the cell. Inside the cell, the cytoplasm is a gel-like substance that suspends the other organelles within the cell and allows for movement. The nucleus of the cell contains DNA and RNA which allow the cell to replicate. Mitochondria provide the energy for the cell, and ribosomes assist with replication.