The circulatory system is an example of an organ system in the human body. Explain why the circulatory system is described as an organ system rather than an organ.

Pearson Edexcel International GCSE Biology (4BI1) — 2.1 Levels of organisation · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

The circulatory system includes the heart, blood vessels and blood, all working together to transport substances around the body.

Model answer (4 marks)

1. An organ is an aggregation of tissues that performs a specific function.
2. An organ system is a group of organs that work together.
3. The circulatory system contains more than one organ, for example the heart and blood vessels.
4. These organs work together to carry out the overall function of transporting substances around the body.

Examiner tips

  • Use the exact phrases from the mark scheme, e.g. "aggregation of tissues" and "group of organs".
  • Show the relationship between the organs and the system – mention the heart and vessels explicitly.
  • Keep each point short and to the point to fit the 4‑mark limit.

Common mistakes

  • Confusing an organ with an organ system – e.g. calling the heart a system.
  • Omitting the fact that the system contains multiple organs.
  • Using vague language such as "body parts" instead of "organs".

Mark scheme (4 marks)

  1. An organ is an aggregation of tissues performing a specific function
  2. An organ system is a group of organs that work together
  3. The circulatory system contains more than one organ, e.g. the heart and blood vessels
  4. These organs work together to carry out the overall function of transporting substances around the body

Key terms in this question

organ system · organ

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