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Levels of Organisation (Edexcel IGCSE Biology)
Revision Note
Cells, Tissues, Organs & Organ Systems
- Cells are the basic building blocks of all living organisms
- Unicellular organisms are made from one cell, whereas multicellular organisms are made up of collections of cells
- Cells are made up of structures called organelles, such as the nucleus, mitochondria and ribosomes
- In complex multicellular organisms:
- Cells are specialised to carry out particular functions
- These specialised cells form tissues
- The tissues form organs
- The organs form organ systems
Different Levels of Organisation Table
Multicellular organisms have many levels of organisation
Examples of Organ Systems in Animals & Plants Table
Worked example
The answer is B: 1 is the leaf organ, 2 is a palisade mesophyll cell and 3 is the spongy mesophyll layer
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