Question 23M.1.SL.TZ1.7

This was another question that candidates found hard. Only about 30% answered correctly and the discrimination index was low, showing that some strong candidates went astray. Answers C and D could be rejected relatively easily as they did not resemble cellulose closely. It was then necessary to select answer A rather than B. Both show polymerized glucose but B shows alpha glucose and branching, which both indicate a molecule of the amylopectin form of starch. A is the correct answer as it shows an unbranched chain of beta glucose. Inconsistencies in the molecular diagrams may have confused some candidates. C6 was shown as a letter C in answer B but it was represented skeletally in answer A, and the two hydrogens bonded to C6 were shown in B but not in A.