A farmer grows soybeans, which are known to be rich in proteins. Explain why proteins are essential for the growth and repair of cells in the human body, and describe the role of monomers in forming protein molecules.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Soybeans are a plant-based food source containing large amounts of protein. When humans digest soybeans, the proteins are broken down and the products are used to build new proteins in the body.
Model answer (5 marks)
Proteins are polymers made of amino‑acid monomers. The amino acids are linked by peptide bonds to form a polypeptide chain, whose sequence determines the protein’s structure and function. In the body, proteins are required for growth and repair because they build new cells, cell structures and tissues. Many proteins act as enzymes, catalysing the chemical reactions that sustain life. Thus, the specific order of amino acids gives each protein a unique role in the cell.
Examiner tips
- Use the term ‘amino‑acid monomers’ and ‘polypeptide chain’ to show knowledge of structure.
- Explain that proteins build new cells and tissues to cover the growth/repair point.
- Mention enzyme activity to hit the catalytic function point.
- Show that sequence determines function to cover the final point.
Common mistakes
- Confusing proteins with carbohydrates or fats.
- Lacking the detail that peptide bonds link amino acids.
- Failing to mention that proteins are used to build new cells and tissues.
Mark scheme (5 marks)
- Proteins are made up of amino acids (monomers)
- Amino acids are joined together to form a polymer (protein chain / polypeptide)
- Proteins are needed for growth and repair because they are used to make new cells / cell structures / tissues
- Proteins can also act as enzymes, which control chemical reactions in cells
- Different sequences / combinations of amino acids produce different proteins with different functions
Key terms in this question
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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