1. Cells: The basic unit of life. Animal cells are eukaryotic, meaning they have a nucleus and other membrane-bound organelles. They perform specialized functions within the body.
2. Tissues: Groups of similar cells that work together to perform a specific function. Examples include muscle tissue, nervous tissue, connective tissue, and epithelial tissue.
3. Organs: Structures composed of different tissues that work together to perform a more complex function. Examples include the heart, lungs, brain, stomach, and skin.
4. Organ Systems: Groups of organs that work together to carry out major bodily functions. Examples include the circulatory system, respiratory system, digestive system, nervous system, and skeletal system.
5. Organism: A complete living being composed of multiple organ systems that work together in a coordinated fashion.
Here's a simple analogy:
Imagine building a house.
* Cells: Like individual bricks
* Tissues: Like the walls, floor, and roof constructed from bricks
* Organs: Like the rooms within the house (e.g., bedroom, kitchen, bathroom)
* Organ Systems: Like the plumbing, electrical, and heating systems that connect and support the rooms
* Organism: The entire house, fully functional and ready to be inhabited
Important Note: This hierarchical organization is a general framework and can vary depending on the specific animal. For example, some simpler animals like sponges lack specialized tissues and organs.