Biology 5090 · O Level · Effects of humans on ecosystems

Effects of humans on ecosystems — practice question

Run-off from fields that have had nitrogen-containing fertilisers applied may cause fish to die in rivers. Which sequence of events explains what happens when fish die because of water pollution by nitrogen-containing fertilisers?

  • Aless oxygen dissolved in the water $\rightarrow$ more growth of water plants $\rightarrow$ more plant decomposition by bacteria
  • Bless oxygen dissolved in the water $\rightarrow$ more plant decomposition by bacteria $\rightarrow$ less plant growth
  • Cmore growth of water plants $\rightarrow$ less plant decomposition by bacteria $\rightarrow$ more oxygen dissolved in the water
  • Dmore growth of water plants $\rightarrow$ more plant decomposition by bacteria $\rightarrow$ less oxygen dissolved in the water

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