Levels of Organisation (Edexcel IGCSE Biology: Double Science)

• 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
• 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

• In humans, the digestive system (provides the body with nutrients) and the respiratory system (provides the body with oxygen and removes carbon dioxide) are examples of organ systems that provide dissolved materials that need to be moved quickly around the body in the blood by the circulatory system

Multicellular organisms have many levels of organisation

Different Levels of Organisation Table

Examples of Organ Systems in Animals & Plants Table

Identifying levels of organisation

• You should be able to identify the different levels of organisation in drawings, diagrams and images of familiar material
• An example of this is shown in the exam question below:

Typical levels of organisation question. The answer is B: 1 is the leaf organ, 2 is a palisade mesophyll cell and 3 is the spongy mesophyll layer