1. Molecule: The smallest unit of a chemical compound, consisting of two or more atoms held together by chemical bonds. Examples: water (H₂O), glucose (C₆H₁₂O₆), DNA.
2. Organelle: A specialized structure within a cell that performs a specific function. Examples: nucleus, mitochondria, ribosomes, Golgi apparatus.
3. Cell: The basic unit of life, capable of carrying out all the processes necessary for life. Examples: nerve cell, muscle cell, blood cell.
4. Tissue: A group of similar cells that work together to perform a specific function. Examples: muscle tissue, nervous tissue, epithelial tissue.
5. Organ: A structure made up of different tissues that work together to perform a specific function. Examples: heart, brain, lungs, stomach.
6. Organ System: A group of organs that work together to perform a major function. Examples: digestive system, circulatory system, nervous system.
7. Organism: A complete living thing made up of multiple organ systems that work together. Examples: human, dog, plant.
Let me know if you'd like more detail on any of these levels!
