Biology 9700 · AS & A Level · Principles of genetic technology
Principles of genetic technology — practice question
When gold occurs alongside mineral ores such as iron sulfide, the sulfides need to be oxidised in order to free the gold particles. Since the mid 1990s, gold has been obtained from these ores by bioleaching. Appropriate bacteria oxidise iron sulfide to soluble iron sulfate, releasing $\text{Fe}^{3+}$ and $\text{SO}_4^{2-}$ ions. This reaction gives out heat energy, and the temperature inside a heap of ore undergoing bioleaching (a bioheap) may reach $70\,^{\circ}\text{C}$ or above. Table 2.1 gives examples of bacteria used in this bioleaching.
(a(i))[1]
Using Table 2.1, suggest a natural habitat for organisms such as $\textit{S. thermosulfidooxidans}$ and $\textit{S. metallicus$.
(a(ii))[3]
With reference to Table 2.1, explain why all three species of bacteria, rather than just one species, are mixed with ore in a bioheap.
(b(i))[3]
With reference to Fig. 2.1, describe how $A.\ ferrooxidans$ affects the oxidation of the ore.
(b(ii))[3]
Explain why bioleaching is now carried out on a large scale worldwide.
(c)[4]
Gold-bearing sulfide ores often contain arsenic, which can be toxic to the bacteria used in bioleaching. However, arsenic-resistant strains of $A.\ ferrooxidans$ have been found in some mines.
The activity of two strains of the bacterium, with and without arsenic ions, is shown in Table 2.2.
Describe the results shown in Table 2.2 and explain the role of natural selection in the evolution of arsenic-resistant bacteria.
Worked solution & mark scheme
This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: “any single option from hot springs / sulphur springs / geysers / geothermal areas / marine vent / volcanic area / hot desert” …