Introduction

Imagine what your body would be like without a skeleton. It would be too soft and squishy to stand up, and would not have the strength for walking or running. Our skeletons are very important for having large, muscular dynamic bodies that can move. Skeletons are important for a whole group of animals, called vertebrates, which like us have bones inside their bodies to support them.

Some of these vertebrates we like to eat: fish, chicken, beef and pork. Their bones are remarkably similar to ours, and are made out of the same mineral calcium. Calcium is important for other parts of the body as well, and vertebrates have found many ways to use calcium to build hard parts of the body like teeth or eggshells. All vertebrates use internal bony skeletons made out of calcium to support their bodies, but how do other animals support their bodies?

Other animals, called invertebrates, use many different strategies to support their body weight. Some invertebrates like earthworms have no hard body parts at all, and use a hydrostatic skeleton that supports the body using water pressure. Other invertebrates, like insects and crustaceans, have hard body parts on the outside of their bodies called an exoskeleton. A good example of this is a crab shell, a hard covering that both protects and supports the body of the crab. Other invertebrates make shells that partially enclose their body, like a snail shell. Some invertebrates, like sea urchins, even use their spiny skeletons for protection from predators.

What are these types of skeletons made of? Are bones and invertebrate exoskeletons made out of the same materials? One way to find out is to use another chemical that reacts with the calcium in bone to test if other hard body parts from other animals are also made out of calcium. You can use common household vinegar to react with the calcium found in bones. Will other animals have calcium in their hard parts too?