Now try the task
Complete the summary below with words taken from the reading passage. Choose ONE OR TWO WORDS AND/OR A NUMBER for each answer.
Medieval alchemists found, in the end, that they could not create gold. Modern geochemists have a similar problem. They find it hard to understand how natural gold deposits form. There is much handwaving about gold-rich fluids from deep in the earth, and chemical precipitation, but biochemical. And a casual experiment conducted by a bacteriologist may hold the key.
Derek Lovley, of the University of Massachusetts, has been studying “metal-eating” bacteria for two decades. These bacteria make their living by converting the dissolved ions of metallic elements from one electrical state to another. This reduction releases energy, which the bacteria extract for their own purposes.
Unsurprisingly, such bacteria tend to prefer common metals such as iron and manganese for lunch, though some species are able to subsist on such exotica as uranium. Dr. Lovley decided to put some of his bacteria into a solution of gold chloride. He was fully prepared for nothing to happen, as gold compounds are generally toxic to bacteria. Instead, the test tube containing the solution turned a beautiful shade of purple, the colour of metallic gold when it is dispersed very finely in water.
Even today, scientists are unable to work out how gold is made. Recently, however, they gave considered that the process may be (4) ______________. An experiment was carried out using bacteria that create their own (5) _________ using metal. The types of metal these organisms usually feed on are either (6) ___________ or ___________. However, when the bacteria were added to a test tube of (7) ___________ solution, it changed (8) ____________, indicating the presence of gold compounds.
6 iron, manganese (not uranium)
7 gold chloride
Find words or phrases in the reading passage about gold bugs that have been replaced by the following words in the summary.
a are unable to work out
b gold is made
c the process
d carried out
f usually feed on
Words found in the passage with similar meaning
a find it hard to understand
b natural gold deposits form
c what is happening
f tend to prefer…lunch