Biology · 2013 · May · Paper 2 · HL · TZ1 · Question paper

24 pages M13/4/BIOLO/HP2/ENG/TZ1/XX Monday 13 May 2013 (afternoon) Biology HigHER lE vEl PaPER 2 INSTRUCTIONS TO CANDIDATES • Write your session number in the boxes above. • Do not open this examination paper until instructed to do so. • Section A: answer all questions. • Section B: answer two questions. • Write your answers in the boxes provided. • A calculator is required for this paper. • The maximum mark for this examination paper is [72 marks]. 2 hours 15 minutes [Personal identifier removed] © International Baccalaureate Organization 2013 Examination code 2 2 1 3 – 6 0 0 8 2213600 8 0124 – 2 – M13/4/BIOLO/HP2/ENG/TZ1/XX Section a Answer all questions. Write your answers in the boxes provided. 1. Isoprene is a chemical synthesized and emitted in large amounts by some plant species, especially oak (Quercus sp.) and poplar (Populus sp.) trees. It has been suggested that isoprene increases the tolerance of plants to high temperatures, which can cause a decrease in photosynthesis rates. Black poplar (Populus nigra) plants were subjected to two raised temperatures and to drought. Measurements of photosynthesis and isoprene emission were made during a 35-day-long drought stress (drought period) and 3 and 15 days after re-watering stressed plants (recovery period). The rate of photosynthesis was recorded as the carbon dioxide taken up per unit of leaf area per second. Isoprene emission / nmol m–2s–1 35 30 25 20 15 10 5 0 25 20 15 10 5 0 drought recovery drought recovery Key: 25 C° 35 C° Rate of photosynthesis / nmol m–2s–1 0 14 30 35 38 50 Time / days [Source: A. Fortunati et al. (2008) “Isoprene emission is not temperature-dependent during and after severe drought-stress: a physiological and biochemical analysis”, The Plant Journal, 55, pages 687–697] (This question continues on the following page) 0224