1. Tissues: Tissues are groups of similar cells that work together to perform a specific function. Examples include muscle tissue, nervous tissue, connective tissue, and epithelial tissue.
2. Organs: Organs are made up of different tissues working together to perform a more complex function. Examples include the heart, lungs, stomach, and brain.
3. Organ Systems: Organ systems are groups of organs that work together to carry out major bodily functions. Examples include the circulatory system, respiratory system, digestive system, and nervous system.
4. Organism: An organism is a complete living being made up of all the organ systems working together.
So, depending on the level of organization you're interested in, the answer could be any of the above!
