WJEC Biology for A2 Level: Revision Workbook

How to use this book Each topic section of the guide begins with around four to eight examination-style practice questions focussed on each topic. The assessment objective being tested is identified for you. The real exam questions will frequently draw from several topics, and from AS/Year 1, so it is important, once you feel confident with the Practice questions, you move on to complete past papers (one is provided for each section in this book), and many are available from the exam board website. This is then followed by some examples of actual student answers to questions. In each case there are two answers given; one from a student (Lucie) who achieved a high grade and one from a student who achieved a lower grade (Ceri). We suggest that you compare the answers of the two candidates carefully; make sure you understand why one answer is better than the other. In this way you will improve your approach to answering questions. Examination scripts are graded on the performance of the candidate across the whole paper and not on individual questions; examiners see many examples of good answers in otherwise low-scoring scripts. The moral of this is that good examination technique can boost the grades of candidates at all levels. This exam preparation guide has been designed to work alongside the Study and Revision Guide, also available by the same author and published by Illuminate Publishing. Practice questions Q1 [AO1] The diagram below summarises the steps in the light-dependent stage of photosynthesis. a) State precisely where the stage takes place. (1) ......................................................................................................................................................................................................................................................................................................................................... b) Name the process by which ATP is produced as shown in the diagram. (1) ......................................................................................................................................................................................................................................................................................................................................... c) Name the group of biological molecules to which ADP belongs. (1) ......................................................................................................................................................................................................................................................................................................................................... d) Explain the role of water in the light-dependent stage. (3) ......................................................................................................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................................................................................................... e) In the absence of NADP, explain the fate of the electrons. (1) ......................................................................................................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................................................................................................... ......................................................................................................................................................................................................................................................................................................................................... increasing energy level electron carriers light AD P + P i AT P chlorophyll chlorophyll light e – 2e – 2e – e – e – e – 3.2 Photosynthesis | 25 Unit 3 Energy, Homeostasis and the Environment Question and mock answer analysis Q & A 1 [a = AO1, b = AO2, c = AO3] 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: a) Suggest why samples were collected in a tube containing hot methanol. Explain 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) c) Suggest what the effect of decreasing light intensity would be on the relative concentrations of TP and RuBP with 0.04% hydrogen carbonate. (3) Lucie’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. ✓ c) Decreasing light intensity means less ATP and reduced NADP, so less TP is made since ATP and reduced NADP are needed to make TP from GP. ✓ Less RuBP ✓ will be produced because RuBP is still being used up to make GP but RuBP is not being regenerated as GP cannot be made into TP, which is needed to make RuBP. ✓ Lucie achieves 8/10 marks air light light algae nutrient medium tub e to collect sample syringe for adding radioactive hydrogen carb onate time 0 . 0 0 8 % CO 2 0 . 0 4% CO 2 G P T P R uB P relative concentration MARKER NOTE Decreasing light intensity means less ATP and reduced NADP, so less RuBP because RuBP is still being used up to make GP but RuBP is not being regenerated as GP cannot be made into TP, which is needed to make RuBP. 3.2 Photosynthesis | 33 Unit 3 Energy, Homeostasis and the Environment 4 | WJEC Biology for A2 Level: Revision Workbook | Introduction Copyright: Sample material