WJEC Biology for A2: Study and Rev Guide

Exam tip It is important that you read the question carefully and give as detailed response as you can. You must name enzymes involved and explain the results in terms of enzyme kinetics, that were covered in AS. Lucie’s answer Ceri’s answer a) Contains hot methanol to denature enzymes to prevent any further reactions ✓ If this was not done further products could be made, e.g. GP could be converted to TP. ✓ b) Decreasing concentration of hydrogen carbonate means that less carbon dioxide is available to join with RuBP to produce GP, so RuBP accumulates. ✓  and therefore less GP can be produced. Any GP present is being converted into TP and so GP falls. ✓ TP concentration falls because of a reducing GP concentration and any TP present will be converted to carbohydrate, so TP is used up. ✓ a) To kill algae to stop reactions ✗  b) Decreasing concentration of hydrogen carbonate causes RuBP concentration to increase. ✗  GP decreases when hydrogen carbonate decreases because GP not being made from RuBP, but is being converted into TP. ✓  Examiner commentary Good answer from Lucie.  The answer could have included that RuBisCO is responsible for fixing carbon dioxide and RuBP and therefore fewer successful enzyme-substrate collisions occur due to the lower concentration of substrate. Lucie achieves 5/7 marks Examiner commentary  Ceri fails to say that enzyme reactions will be stopped: This is important as GP could be further converted to TP unless enzymes are denatured.  This is purely descriptive: There is no link made between hydrogen carbonate and carbon dioxide concentrations, and there is no mention of the enzyme involved RuBisCO or enzyme kinetics.  Ceri fails to mention the reasons for a decrease in TP: That TP is being converted into carbohydrate. Ceri achieves 1/7 marks 169 Questions and answers Q & A 1 Unit 3 Photosynthesis An experiment was carried out using algae in Calvin’s lollipop flask. At regular intervals over one hour, samples were removed into a tube which contained hot methanol. The products were identified and their masses measured using mass spectroscopy. The experiment was carried out once using 0.04% hydrogen carbonate and repeated using 0.008%. The relative masses of glycerate-3-phosphate (GP), triose phosphate (TP) and ribulose bisphosphate (RuBP) are shown on the graph below. air light light algae nutrient medium tube to collect sample syringe for adding radioactive hydrogen carbonate Time 0.008% CO 2 0.04% CO 2 GP TP RuBP Relative concentration Calvin’s lollipop apparatus Results graph a) Suggest why samples were collected in a tube containing hot methanol, explaining why results would be less reliable if this were not done. (2) b) Describe and explain the effect of decreasing hydrogen carbonate concentration on the relative concentrations of GP, TP and RuBP. (5)