Final answer:
The levels of organization in the human body, from least to most complex, are cells, tissues, organs, and organ systems.
Step-by-step explanation:
The levels of organization of the human body in order from least (top) to most complex are:
- Cells: Cells are the basic structural and functional units of the body. They can be specialized for specific functions such as muscle cells or nerve cells.
- Tissues: Tissues are groups of similar cells that work together to perform a specific function. Examples include epithelial tissue, connective tissue, muscle tissue, and nervous tissue.
- Organs: Organs are composed of different tissues working together to perform a specific task. For example, the heart is an organ made up of cardiac muscle tissue, connective tissue, and nervous tissue.
- Organ systems: Organ systems are groups of organs that work together to perform a particular function. Examples include the digestive system, circulatory system, and respiratory system.