The bones of the skeleton have five major functions. some bones protect soft body parts. for example, the sternum, thoracic vertebrae, and protect the heart and lungs.

The sternum, thoracic vertebrae, and ribs protect the heart and lungs.

Explanation:

The skeleton can be divided into the axial skeleton (the skull and the vertebral column), visceral skeleton (ribs and sternum) and the appendicular skeleton (extremities).

The function of the visceral skeleton is to support and protect the first portion of the digestive and cardio-breathing apparatus.

In mammals, the second part of the vertebral column (thoracic vertebrae), the ribs and the sternum delimitate a protective box for lungs and heart.  

mammal

explanation:

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.