Biology · 2014 · May · Paper 2 · SL · TZ2 · Question paper

20 pages M14/4/BIOLO/SP2/ENG/TZ2/XX Friday 9 May 2014 (afternoon) BIOLOGY STANDARD LEVEL 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 one question. • Write your answers in the boxes provided. • A calculator is required for this paper. • The maximum mark for this examination paper is [50 marks]. 1 hour 15 minutes © International Baccalaureate Organization 2014 Examination code 2 2 1 4 – 6 0 1 7 [Personal identifier removed] [Personal identifier removed] – 2 – M14/4/BIOLO/SP2/ENG/TZ2/XX 20EP02 SECTION A Answer all questions. Write your answers in the boxes provided. 1. Ozone gas in the atmosphere helps to block high-energy ultraviolet light (UV) from reaching the Earth’s surface. Over the past few decades, the ozone layer has been decreasing, thus allowing through more UV. The effect of this decrease in the ozone has been studied in different plants. An early study was undertaken on patience dock plants (Rumex patientia ) to test the effect of atmospheric ozone levels decreasing by 38 %. The net photosynthesis (total photosynthesis minus total respiration) and respiration of the plants were measured during seven days of exposure to UV . The rates of photosynthesis and respiration are given in rates of carbon dioxide uptake per unit area of leaf. Net photosynthesis / mg CO 2 dm–2 hr–1 13 12 11 10 9 8 0 0 1 2 3 4 5 6 7 Days of treatment Respiration / mg CO2 dm–2 hr–1 0 –1 –2 –3 increasing respiration 0 1 2 3 4 5 6 7 Days of treatment Key: control plants exposed to UV with 38 % less ozone [Source: Adapted from W. Sisson and M. Caldwell (1976), ‘Morphological responses of crop and weed species of different growth forms to Ultraviolet-B radiation’, Plant Physiology, 58, pages 563–568. www.plantphysiol.org © American Society of Plant Biologists.] (This question continues on the following page)