Cell Organisation: Tissues, Organs and Organ Systems — AQA GCSE Biology
Living organisms are organised into increasingly complex levels of structure.
Levels of organisation
Cells → tissues → organs → organ systems → organism.
- A tissue is a group of similar cells working together to perform a function.
- An organ is a group of different tissues working together to perform a function.
- An organ system is a group of organs working together to perform a function.
- The organism is the whole living thing.
Examples
- Tissue: muscle tissue (contracts), glandular tissue (makes enzymes), epithelial tissue (covers).
- Organ: the stomach contains muscle tissue (churning), glandular tissue (enzymes and acid) and epithelial tissue (lining).
- Organ system: the digestive system includes the stomach, small intestine, pancreas and liver, all working together to digest and absorb food.
Why organisation matters
Larger organisms need this organisation because individual cells cannot meet all the body's needs alone. Specialised tissues and organs allow efficient exchange and transport of substances throughout the body.
Exam tips
- Learn the order: cells → tissues → organs → organ systems → organism.
- Define each level precisely (tissue = similar cells; organ = different tissues).
- Use the stomach and digestive system as ready examples.
- Be able to identify the level a given structure belongs to.