Q47 - Nutrient Limitation of Baltic Phytoplankton Groups

Theoretical B Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Countries around the Baltic Sea have agreed to reduce the outlet of nutrients in drainage water, especially N. In a study, growth of diatoms, N-fixing cyanobacteria and dinoflagellates was monitored together with the seawater N: P ratio to estimate the effects of outlet reduction. Optimum N: P ratio for growth in the three groups is approximately 7.

Annual variation in biomass of the three study groups (A) and seawater N: P-ratio (B) (from FF 1998).

Figure 1. Figure 1.

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

A. The limiting factor for diatoms during the winter (January-March) is N

B. The limiting factor for phytoplankton during the summer (June-Aug.) is P

C. Less N from drainage water will, in particular, reduce growth of cyanobacteria

D. Autotrophic dinoflagellates begin to increase dramatically in number in early spring (March), because of their mobility

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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)