* Cells: The fundamental building blocks of all living organisms, including humans. They are considered the smallest unit of life capable of independent function.
* Tissues: Groups of similar cells that work together to perform a specific function. Examples include muscle tissue, nervous tissue, and epithelial tissue.
* Organs: Structures made up of different tissues that work together to carry out a complex function. Examples include the heart, lungs, and brain.
* Organ systems: Groups of organs that work together to perform a major bodily function. Examples include the circulatory system, respiratory system, and digestive system.
If you can provide more context or clarify what you're looking for, I may be able to give you a more precise answer.
