Here's why:

* Tissues are groups of similar cells that work together to perform a specific function.

* Organs are made up of different tissues that cooperate to carry out a more complex function.

For example, the heart is an organ. It contains:

* Muscle tissue for contraction and pumping blood.

* Connective tissue to provide structure and support.

* Epithelial tissue lining the chambers of the heart.

* Nervous tissue to regulate the heart's rhythm.

So, the various tissues working together create the complex functionality of an organ.