Level of life
Tissue
A group of similar cells working together, such as muscle, nerve or leaf tissue.
Organ
Several tissues combined into a structure with a particular job, such as the heart, a kidney or a leaf.Source: OpenStax, 2022Source: OpenStax, 2018
Level of life
How Organ connects
Organ is made of
Organ makes up
Level of life
Organism
An individual living thing, from a single bacterium to a tree or a person.
Structure
Organ systems
Groups of organs that work together, such as the circulatory, respiratory, digestive and urinary systems.
Organ includes the example
Structure
Brain
The organ that controls thought, movement and many body functions. It holds neurons and other cells in roughly equal numbers.
Studied in
Your progress
Sources & further reading
The explanations on this page are our own summaries of these sources. Follow a link to read the original; if anything here disagrees with it, the original wins. How we choose and check sources.
Anatomy and Physiology 2e (opens the original in a new tab)
OpenStax (2022). OpenStax, Rice University.
TextbookEducationalLicence: CC BY-NC-SA 4.0 (linked, not reused)
Biology 2e (opens the original in a new tab)
OpenStax (2018). OpenStax, Rice University.
Free introductory college textbook.
TextbookEducationalLicence: CC BY-NC-SA 4.0 (linked, not reused)