A tissue is made of cells of a single type, working together. An example is striated muscle tissue which enables us to perform voluntary movements in the body. Another example is epithelial tissue which lines organs inside the body. The lining of the mouth contains epithelial tissue. An organ is composed of several different types of tissue working together to perform a function. An example of an organ is the heart. Tissues that make up the heart include--blood, nerve, connective, muscle, and epithelial tissues. When these tissues work together, the job of the heart can be performed. The heart is able to pump blood to the lungs and to all the systems of the body, constantly throughout a person's life. However, the heart is only one part of the organ system known as the transport or circulatory system. An organ system is composed of several types of organs working together to carry out a life process, in this case transport. The organs in the transport system include the heart, arteries, capillaries and veins. Organ systems work together to maintain homeostasis within an organism.