The five levels of organisation
Cell β tissue β organ β organ system β organism.
Living things are built in a hierarchy, each level more complex than the one below:
- Cell β the basic unit of life. A single nerve cell, a single muscle cell.
- Tissue β a group of similar cells working together. Muscular tissue, epithelial tissue.
- Organ β different tissues grouped to do a specific job. Heart, liver, stomach, leaf.
- Organ system β multiple organs working together for a complex function. Digestive system, circulatory system.
- Organism β the whole individual.
Three tissues you should know in the digestive system:
| Tissue | Function |
|---|---|
| Muscular tissue | Contracts to mix and move food along (peristalsis) |
| Glandular tissue | Produces and releases substances such as enzymes and hormones |
| Epithelial tissue | Covers organs and lines internal cavities like the gut |
Cells make tissues; tissues make organs; organs make organ systems.
Tissue = SIMILAR cells working together for ONE function.
Organ = DIFFERENT tissues working together for ONE specific function.
Organ system = multiple organs cooperating.
Common pitfall
Calling 'the cardiac muscle' an organ. Cardiac muscle is a TISSUE; the HEART (which contains cardiac muscle plus other tissues) is the organ.