Principles of Organisation in GCSE Biology
Learn how cells form tissues, tissues form organs and organs form organ systems, with a clear GCSE Biology example and common exam mistake to avoid easily.
The principles of organisation describe how cells are organised into tissues, organs, organ systems and finally a complete organism.
The order is:
cells→tissues→organs→organ systems→organism\text{cells} \rightarrow \text{tissues} \rightarrow \text{organs} \rightarrow \text{organ systems} \rightarrow \text{organism}cells→tissues→organs→organ systems→organismWhat does each level mean?
- Cells are the basic building blocks of living organisms. Different cells may be specialised to perform particular functions.
- A tissue is a group of cells with a similar structure and function.
- An organ is made from different tissues working together to perform a particular function.
- An organ system is a group of organs working together to carry out an important body function.
- An organism is the complete living thing formed from its organ systems.
Each level becomes more complex because it contains organised parts from the level below.
How to identify the level
Look at what the structure contains and what it does. If it is made of similar cells, it is a tissue. If several tissues perform one function, it is an organ. If several organs cooperate, it is an organ system.
Worked example: the circulatory system
A muscle cell is specialised to contract. Many muscle cells form muscle tissue. Muscle tissue is one of the tissues that makes up the heart.
The heart is an organ because it contains different tissues working together to pump blood. The heart works with blood and blood vessels as part of the circulatory system. This organ system transports substances around the organism.
Another example is the digestive system. Organs including the stomach and small intestine work together to digest food and absorb soluble molecules.
Common exam mistake
Do not describe an organ as a group of similar cells. That is a tissue. An organ contains different tissues working together, while an organ system contains different organs working together.
Assumption: this answer is for separate-science AQA GCSE Biology 8461. No tier was specified, but these principles apply to both Foundation and Higher tiers.
