A doctor is explaining to a medical student how the human body is made from a small number of chemical elements. The doctor states that just six non-metallic elements account for over 99% of the mass of the human body, and that the most abundant element in the universe is also found in the body. Explain which elements make up most of the human body, how these elements were formed, and why carbon is particularly important for living organisms.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Just six non-metallic elements account for over 99% of the mass of the human body. The most abundant element in the universe is also found in living organisms.
Model answer (5 marks)
The six main non‑metallic elements are hydrogen, oxygen, carbon, nitrogen, phosphorus and sulphur.
Hydrogen was produced in the Big Bang.
The heavier elements were formed by nuclear fusion in stars.
When stars explode as supernovae these elements were dispersed into space and later incorporated into the Earth and living organisms.
Carbon can form four covalent bonds and can bond to itself, giving rise to long chains and rings, which allows the vast diversity of complex organic molecules required for life.
Hydrogen was produced in the Big Bang.
The heavier elements were formed by nuclear fusion in stars.
When stars explode as supernovae these elements were dispersed into space and later incorporated into the Earth and living organisms.
Carbon can form four covalent bonds and can bond to itself, giving rise to long chains and rings, which allows the vast diversity of complex organic molecules required for life.
Examiner tips
- Use the exact element names; include sulphur not sulfur
- Show the sequence: Big Bang → stellar fusion → supernova dispersal → incorporation into life
- Explain carbon’s tetravalency and ability to self‑bond for complexity
Common mistakes
- Omitting sulphur or using the wrong spelling
- Failing to mention the Big Bang for hydrogen
- Not linking supernovae to element distribution
Mark scheme (5 marks)
- Identifies hydrogen, oxygen, carbon, nitrogen, phosphorus, and sulfur as the six main elements in the human body (accept any four correctly named for this mark)
- States that hydrogen was formed in the Big Bang
- States that the other elements (heavier than hydrogen) were formed by nuclear fusion in stars
- States that these elements were distributed across the universe when stars exploded (supernovae) and eventually became part of the Earth and living organisms
- Explains that carbon can form four bonds and bond to itself to make long chains or rings, allowing a huge variety of complex molecules needed for life
Key terms in this question
Related
- All OCR A-Level Chemistry B: Salters (H433) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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