Question

what happens if our backbone is made up of one long bone

Answer 1

If our backbone was indeed made up of a single long bone, we would not be able to bend as we do, thus losing the advantages of the elasticity that we possess

Answer 2

Human backbone provides support to our body and helps in the movement. The structural composition of back bone allows us to bend, crouch, stand and lie down on the ground. The vertebral units promote this movement.

If back bone is made up of one long bone then we would never be able to sit, crouch or lie. One single bone means no flexibility in the structure of a bone.