A bone is tissue. It forms a part of the skeletal system which is made up bones, joints, ligaments and cartilage. Cells work together in groups known as tissues. A tissue is defined as a group of similar cells working together to carry out a certain task. Examples are skin, bone, blood. Tissues in turn are grouped together to form organs. An organ is defined as a group of tissues that work together to carry out a certain task . Examples are heart, lungs, liver.