Final answer:
An arthropod shed its old exoskeleton during molting, which is essential for growth as the exoskeleton does not expand. This process allows the arthropod to accommodate increases in size and weight.
Step-by-step explanation:
An arthropod shed its old exoskeleton during molting. Molting is a process necessary for an arthropod's growth because the exoskeleton does not expand as the animal grows. The arthropod must synthesize a new exoskeleton beneath the old one, and then it sheds the original covering. This is essential since the exoskeleton provides protection, and support, and prevents water loss, but also limits growth. Therefore, to increase in size and accommodate weight changes, the arthropod must shed its exoskeleton, in a process also known as ecdysis.