Here's why:

* Organelles are subcellular structures within a single cell, not groups of cells.

* Cells with similar functions aggregate to form tissues, not organelles.

* Organelles are made up of different biomolecules like proteins, lipids, and nucleic acids, not other cells.

Think of it this way:

* Organelles are like the different departments within a factory (e.g., the mitochondria are like the power plant).

* Cells are like the individual workers in the factory.

* Tissues are like groups of workers performing similar tasks in the factory (e.g., the assembly line).

Let me know if you have any other questions about cells or organelles!