Cells, tissues, organs and organ systemsSpec 4.2.1
Living things are built up in levels. Each level is made from the one below it.
- Cell
- The basic building block of all living organisms.
- Tissue
- A group of cells with a similar structure and function.
- Organ
- An aggregation of tissues performing specific functions.
- Organ system
- Organs are organised into organ systems, which work together to form organisms.
The stomach is a good example of an organ. It is made of several tissues that work together. Muscular tissue churns the food, glandular tissue makes digestive juices (enzymes and acid), and epithelial tissue covers the inside and outside surfaces.
The stomach is one of the organs in the digestive system. This is an organ system: several organs working together to digest and absorb food.
| Level | Animal example | Plant example |
|---|---|---|
| Cell | A muscle cell | A palisade mesophyll cell |
| Tissue | Muscular tissue | Palisade mesophyll |
| Organ | The stomach or the heart | A leaf |
| Organ system | The digestive system or the circulatory system | Roots, stem and leaves (transport system) |
| Organism | A human | A tree |
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