2 Vertebrates-Mid

Vertebrates Written by Kira Freed

Introduction Knock on your forehead. The hard thing you feel inside your head is bone. Bones hold up your body and protect organs such as your brain and heart. Scientists sort animals into two groups. Vertebrates have backbones. Invertebrates do not have backbones. Let's learn about the five groups of vertebrates. Think about what the groups have in common and how they are different.

A Closer Look at Bones All bones are made of a hard kind of body tissue. (Skin and muscles are other kinds of tissue.) Without bone tissue, your body would just be a big, soft blob. If you've ever seen a bone, you may think it looks dry and lifeless. But the bones inside your body are alive! Some bone cells help to mend broken bones. Others make blood cells. These bone cells are found in bone marrow, a special tissue in the middle of some larger bones.

The skeleton is the strong frame that supports and protects a vertebrate's body. The spine, or backbone, is the special feature of vertebrates. The spine is made up of a chain of bones. At the top of the spine is the skull. It holds and protects the body's control center— the brain. Your skeleton has 206 bones. Other kinds of vertebrates have different numbers of bones.

The ends of many bones are covered with cartilage. Cartilage is soft, rubbery tissue that keeps bones from grinding against each other. Other body parts have cartilage, too. Your nose and ears are made of cartilage. Joints are the places where bones meet. Joints let vertebrates move in different ways. Some joints, such as your knees, only bend one way. Other joints, such as your shoulders, rotate. The joints in your spine can twist and turn. Cartilage helps all these joints to move smoothly.

Different bones have different jobs. Leg bones support the weight of an animal while it walks or runs. Most flying vertebrates have hollow bones so they weigh less in the air. The bones in feet, hands, flippers, and wings help animals to move their bodies or handle food.