Plant structure and function

Sample questions

Original practice questions written in the style of the exam.

1. Question 13 marks

   Seedlings were grown in culture solutions each lacking one mineral ion.

   Explain why seedlings lacking magnesium ions had yellow leaves, and state why plants need nitrate ions.

   Mark scheme

   • Magnesium ions are needed to make chlorophyll (1)
   • Without chlorophyll the leaves are yellow (chlorosis) (1)
   • Nitrate ions are needed to make amino acids / proteins / nucleic acids (1)
2. Question 24 marks

   Explain how the structure of xylem vessels is related to their function.

   Mark scheme

   • Cells are dead with no cytoplasm and no end walls, forming a continuous hollow tube for water to flow through (1)
   • Walls are thickened with lignin, which strengthens them so they do not collapse under tension (1)
   • Lignin also makes the walls waterproof (1)
   • Pits in the walls allow water and mineral ions to move sideways between vessels (1)