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Q45 - Light and Depth Effects on Photosynthesis in a CAM Aquatic Plant

Theoretical B Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Calvin Cycle, Photorespiration & C4/CAM Biochemistry

The relationship between light intensity and net photosynthesis rate (NPR) was measured in the submerged plant Crassula helmsii in a lake. The plant has CAM photosynthesis. Measurements of the photosynthetic rate (μmol O2 mg-1 chlorophyll h⁻¹) were made on plants growing in shallow water (6.5 mg chlorophyll/g dry weight) and deep water (10.3 mg chlorophyll/g dry weight) in April and July (Fig.).

Light response curves in April and in July for C. helmsii, growing in shallow (0.5 m) and deep (2.2. m) water. PAR photosynthetically active radiation (from Klavsen & Maberly 2009).

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. Shallow-water plants have higher NPR at 100 PAR than deep-water plants
B. Deep-water plants have higher NPR in July than in April
C. In the experiment, NPR is light limited
D. Deep-water plants have a higher NPR because of their higher chlorophyll content
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Question reproduced from IBO 2015, Theoretical Exam B, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)