Photosynthesis

Sample questions

Original practice questions written in the style of the exam.

1. Question 12 marks

   Pigments from a leaf were separated by thin-layer chromatography. One pigment spot moved $4.2\,\text{cm}$ from the origin while the solvent front moved $9.6\,\text{cm}$.

   Pigment	$R_f$ in this solvent
   carotene	0.95
   xanthophyll	0.71
   chlorophyll a	0.44
   chlorophyll b	0.32

   Calculate the $R_f$ value of the spot and identify the pigment.

   Mark scheme

   • $R_f = 4.2 \div 9.6 = 0.44$ (1)
   • Chlorophyll a (1)
2. Question 25 marks

   Describe the light-independent reactions of photosynthesis.

   Mark scheme

   • Carbon dioxide combines with ribulose bisphosphate (RuBP), catalysed by RUBISCO (1)
   • Forming two molecules of glycerate 3-phosphate (GP) (1)
   • GP is reduced to glyceraldehyde 3-phosphate (GALP) using reduced NADP (1)
   • ATP from the light-dependent reactions provides the energy for this reduction (1)
   • Most GALP is used to regenerate RuBP (using ATP), and some is used to make glucose / other organic molecules (1)