Final answer:
Hydrostatic skeletons consist of a fluid-filled cavity that provides support through hydrostatic pressure, while exoskeletons are hard external coverings that provide protection and support. The correct answer to the student's question is option a), highlighting the different ways through which each type of skeleton protects internal organs.
Step-by-step explanation:
The various types of skeletons seen in biology serve the same essential functions but do so in different ways. When contrasting hydrostatic skeletons with exoskeletons, it is important to note that:
- A hydrostatic skeleton is characterized by a fluid-filled cavity, known as the coelom, which provides structural support and protection by resisting external compression through hydrostatic pressure. This type of skeleton allows for movement by the contraction of surrounding muscles that change the shape of the coelom, as seen in soft-bodied animals like earthworms and sea anemones.
- On the other hand, an exoskeleton is a rigid, hard covering that exists on the exterior of an organism. It serves to protect and support the body, enabling movement through the contraction of muscles attached to the inside of the skeleton. Exoskeletons are found in arthropods like crabs and lobsters, and are usually composed of materials such as chitin, sometimes reinforced with calcium carbonate.
Option a) is the correct answer to the question, as it describes these contrasting functions properly. To clarify further:
- Hydrostatic skeletons are internal and use the pressure of enclosed fluid for support, while exoskeletons are external and protective hard casings.
- Exoskeletons must be shed and regenerated as the organism grows since they do not expand, unlike hydrostatic structures which do not have this limitation.
- Moreover, exoskeletons also provide less mechanical leverage than endoskeletons do.