Biology 9700 · AS & A Level · Testing for biological molecules
Testing for biological molecules — practice question
In some ecosystems, the soil contains very low concentrations of nitrate ions. Certain flowering plant species can obtain the nitrogen they require from other sources. Carnivorous plants have leaves that are modified to trap animals. The leaves of $\textit{Drosera rotundifolia}$ have hairs around each leaf that secrete a sticky solution. Insects, such as the one shown in Fig. 5.1, adhere to this solution. The leaves then curl around the insect and release enzymes to digest its body.
(a)[4]
Explain why $D.\,rotundifolia$ may be regarded as both an autotroph and a heterotroph.
(b)[3]
In 1999, Dutch scientists identified a new reaction, the anammox reaction, to be added to the nitrogen cycle. They discovered the bacterium $\textit{Brocadia anammoxidans}$ that turns ammonia, nitrite ions and nitrate ions into nitrogen gas $(\text{N}_2)$ in anaerobic environments. The process carried out by these bacteria is believed to cause the loss of a large amount of nitrogen-containing compounds from marine ecosystems, such as the oceans. Suggest and explain the effect that this reaction has on marine ecosystems.
Worked solution & mark scheme
This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Autotroph uses light energy in photosynthesis” …