Here's why:
* Cells are the basic building blocks of life.
* Tissues are groups of similar cells that perform a specific function. Muscle tissue, for example, is responsible for movement.
* Organs are made up of different tissues working together. For example, the heart is an organ made up of muscle tissue, connective tissue, nervous tissue, and epithelial tissue.
* Organ systems are groups of organs that work together to carry out a major body function. For example, the muscular system is made up of all the muscles in the body.
So, a group of similar cells like muscle cells work together within a tissue to perform a specific function.
