Resources | Subject Notes | Biology
This section explains the fundamental levels of biological organization, starting with the basic unit of life and progressing to complex living beings.
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that can replicate independently.
A tissue is a group of similar cells that perform a specific function. For example, muscle tissue is responsible for contraction, and nervous tissue transmits electrical signals.
An organ is a structure composed of two or more different tissues that work together to perform a particular function. Examples include the heart, lungs, and stomach.
An organ system is a group of organs that work together to perform a major function in the body. Examples include the digestive system, circulatory system, and nervous system.
An organism is a complete, living individual. It is made up of one or more organ systems working together to maintain life.
| Level of Organization | Definition | Example |
|---|---|---|
| Cell | Basic structural and functional unit of life. | Muscle cell, Nerve cell |
| Tissue | Group of similar cells performing a specific function. | Muscle tissue, Nervous tissue |
| Organ | Structure composed of two or more tissues working together. | Heart, Lungs, Stomach |
| Organ System | Group of organs working together to perform a major function. | Digestive system, Circulatory system |
| Organism | A complete, living individual. | A human, a plant, a bacterium |