Edexcel IGCSE Biology

Revision Notes

2.1.1 Levels of Organisation

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
  • 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

Different levels of organisation in organisms 1, downloadable AS & A Level Biology revision notes downloadable AS & A Level Biology revision notes
Multicellular organisms have many levels of organisation

Different Levels of Organisation Table

Different Levels of Organisation Table, downloadable AS & A Level Biology revision notes

Examples of Organ Systems in Animals & Plants Table

Tissue Examples table, IGCSE & GCSE Biology revision notes

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, IGCSE & GCSE Biology revision notes

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

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Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. With 10 years of teaching experience across the 3 key science disciplines, Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.

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