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Q29 - How a Burrowing Polychaete Alters Sediment Nitrogen Cycling

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

The polychaete Nereis virens lives in the bottom sediment of shallow coastal waters. It digs tunnels in the sediment and pumps water through these tunnels. The decomposition turnover of nitrogen (N) compounds has been investigated in the sediment at two sites: one without Nereis (Fig. A) and one with 600 Nereis per m² (Fig. B).

Sediment N-processes without (A) and with (B) Nereis. Numbers at arrows give the annual N turnover in g N per m² per year.

Figure 1. Figure 1.

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

A. Less organic N is deposited in the bottom sediment in B compared to A
B. Denitrification rate is increased threefold in the presence of Nereis
C. In the tunnels made by Nereis, 5 g N per m² per year are deposited in the sediment
D. Concentrations of nutrients, which may lead to algal bloom, are lowered in the presence of Nereis
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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)