The basic structural unit of the body is the: heart brain cell tissue

Cells are considered the basic structural units of the body.
Cells are what make up the tissues that compose organs such as the heart and the brain. 

Ifound this on google “aristotle (384–322 bc) in western scientific taxonomy the greek philosopher aristotle was the first to classify all living things, and some of his groups are still used today, like the vertebrates and invertebrates, which he called animals with blood and without blood.” i hope this you for what your looking for.