Questions 15 to 21 are based on the following passage.
Most scientific research follows a logical progression, with one experiment following up on the findings of another. Every now and then, however, coincidence plays a part. Such is the case with a paper just published in Current Biology, which reveals to the world a moth capable of chewing up plastic.
The experiment behid the paper was inspired when Federica Bertocchini, an amateur beekeeper who is also a biologist at Cantabria University, in Spain, noticed caterpillars chewing holes through the wax in some of her hives and lapping up the honey. To identify them, she took some home in a plastic shopping bag. But when, a few hours later, she got around to look at her captives she found the bag was full of holes and the caterpillars were roaming around her house. After rounding them up, she identified them as larvae of the greater wax moth, a well-known pest of bee hives. On considering their escape from their shopping-bag prison, though, she wondered whether they might somehow be put to work as garbage-disposal agent.
Past attempts to use living organisms to get rid of plastics have not gone well. Even the most promising species, a bacterium called Nocardia asteriodes, takes more than six months to destroy a film of plastic a mere half milimetre thick. Most identified organisms were just not efficient enough. Judging by the job they had done on her bag, Dr Bertocchini suspected wax-moth caterpillars would perform much better than that.
To test this idea, she teamed up with Paulo Bombelli and Chrostopher Howe, two biochemists at Cambridge University. Dr Bombelli and Dr Howe pointed out that, like beeswax, many plastics are held together by methylene bridges, which are structures that consist of one carbon and hydrogen atoms, with the carbon also linked to the other atoms. Few organisms have enzymes that can break such bridges, which is why these plastics are not normally biodegradable. The team suspected wax moths had cracked the problem.
However, they decided to put the moths to a greater test. One of the most persistent constituents of rubbish dumps is polyethylene, which is composed exclusively of methylene bridges linked to one another. So it was on polyethylene that the trio concentrated. When they put wax moth caterpillars onto the sort of film it had ta ken Nacordia asteroides half a year to deal with, they found that holes appeared in it within 40 minutes.
On closer examination, Dr Bertocchini and her colleagues discovered that their caterpillars, each ate an average 2.2 holes, three milimetres across, every hour, in the plastic film. A follow up test found a caterpillar took about 12 hours to consume a milligramme of shopping bag. Such bags weigh about three grammes, so 100 larvae might, if they spent half their lives, eating, consume one in a month.
Whether releasing wax moths on the world’s surplus plastic really is sensible is not yet clear. For one thing, it has not been established whether the caterpillars gain nutritional value from the plastics they eat, as well as being able to digest them. If they do not, their lives as garbage-disposal operatives are likely to be short – and, even if they do, they will need other nutrients to thrive and grow. Another question is the composition of their faeces. If these turn out to be toxic, then there will be little point in pursuing the matter.
Regardless of this, though, the discovery that the wax-moth larvae can eat plastic is intriguing. Even if moths themselves are not the answer to the problem of plastic waste, some other animal out there might be.
15. Federica Bertocchini’s research was based on
- a previous research
- an unexpected incident
- an article from Current Biology
16. What is paragraph 2 about?
- Federica’s work as a biologist
- The discovery of plastic eating moths
- The caterpillars escape from the shopping bag
17. Previous attempts of using living organisms to destroy plastic were unsuccessful because
- is difficult to extract Nocardia asteroides
- they take too long to consume the plastics
- they could not destroy thick plastics
18. The team suspected wax moths had cracked the problem (paragraph 4). What is the problem?
- Time taken to break down the plastics
- Breaking down the methylene bridges
- Finding organisms to break the bridges
19. The word constituents (paragraph 5) means
20. The purpose of paragraph 7 is to discuss
- The feasibility of using wax moths for breaking down plastics
- the risks of toxins emitted by wax moths
- the nutritional needs of wax moths
21. In the last paragraph the researchers are ___________________ about solving the problem of plastic waste using organisms.
Question 22 to 29 are based on the following passage.
Planting vegetables at home
As a mother an chef of the house, it has become my routine to buy groceries every week. Amid the slow economy, increase in fuel price and climate change, I have witness the rather drastic price increase of fruits and vegetables. The idea of growing my own vegetables did cross my mind but I always often held back due too many reasons, including the hassle of handling soil, expensive fertilisers, pesticide control as well as the amount of time and energy needed to take care of the plants. However, talking to James Phe has made me think seriously about planting vegetables at home.
To James Phe, who first tried out the soilless planting method more than 20 years ago using a hydroponic starter-pack, planting vegetables at home is easy but yet at the same time, requires a lot of patience and effort. The main problem with soil-based gardening is the weeds and soil-bornepests that make it necessary to constantly fertilise the soil. The heavy digging, the composition of soil and the amount of water required are other factors which make soil-based gardening unattractive to people who are thinking of planting vegetables for home consumption.
The word hydroponics first appeared in 1973, William Gericke, a scientist at the University of California, created the word to refer to growing of plants in some medium other than soil. However, it was Julius Von Sachs, a researcher in plant nutrition, who pioneered modern hydroponics. Hydroponics was initially often used to grow plants for research purposes but in the last 50 years, hydroponics has been used on a commercial basis. How hydroponics appear to have made inroads as a hobby, to people like James Phe.
Phe said he did some research on hydroponics gardening methods which require continuous monitoring on the amount of water and sunlight for the vegetables to grow. In hydroponics gardening, soil is substitute by liquid nutrients comprising nitrogen, phosphorus, potassium and trace elements. With hydroponics, plants take a shorter time to grow and less pesticide is needed. Cost-wise it depends on how elaborate the hydroponics system is. In a full specification, the initial cost for the whole set is rather high and there is a high maintenance cost as well. For an automatic watering system, electricity is required to support the system.
For the first 10 years, Phe grew many different kinds of vegetables like tomatoes, mustard, lettuce and eggplants as well as fruits using hydroponic systems which his wife helped to mind. After his wife passed away, he buried himself in his day job as manpower supplier in the oil and gas industry and his gardening hobby was put aside along with his many memories of his wife.
When Phe retired more than a couple of years ag, he picked up where he had left off. This time Phe ventured into the technology of aquaponics, a method he found to be much more efficient compared to hydroponics. His experience with hydroponics made it easier for him to venture into aquaculture.
Aquaponics is a combination of aquaculture and hydroponics technology by growing plants and fish in one integrated system. The fish waste provides an organic food source for the growing plants and the plants become a natural filter for the water, supplying clean, purified water back into the fish tank. Within the system, microbes convert the ammonia from the fish waste into nitrites as food for the plants. This is not only a great way to capitalise on the benefits, it also helps cut down the cost of maintenance and saves water. Aquaponics uses much less water compared to soil-based gardening and hydroponics.
However, aquaponics may fail if the fish is not taken care of first. As the environment may not be naturally healthy for the fish, there is a need to use medicines like antibiotics to protect them. Higher ammonia may occurin the fish caused by fish urine and waste.This is a pitfall that novices in aquaponics may fall into but Phe knows a secret of converting them to nitrites which are needed for plant growth.
Every now and then, Phe receives visits from students wanting to learn about aquaponics. Most recently were students from PACTS Education Clubhouse. He showed them the system he built from scratch and proudly showed them the healthy plants he had grown.
22. The writer begins the passage with
- how James Phe inspired her to grow her own vegetables
- reasons why she did not plant her own vegetables
- causes for the increase in vegetable prices
23. In paragraph 3, the writer’s intention is to
- show that it is a sound scientific method of growing plants
- explain the changes in the use of hydroponics over time
- highlight the pioneering efforts in hydroponics
24. Paragraph 4 is developed mainly through
- comparison and contrast
- problem and solution
- cause and effect
25. Why did Phe stop hydroponic gardening for some time?
- Too much of his time and energy was spent on hydroponic gardening
- Hydroponic gardening reminded him of his wife
- His day job became too demanding
26. The following explains why aquaponics is better than hydroponics except
- aquaponics is less costly
- aquaponics uses less water
- aquaponics uses less fertiliser
27. One difficulty of aquaponics is
- maintaining a healthy environment for the fish
- using the right amount of antibiotics on fish
- getting rid of fish urine and waste
28. pitfall (paragraph 8) means
29. It can be inferred from the last paragraph that
- people are now concerned about healthy eating
- students are interested to study plant nutrtion
- Phe has become an expert in aquaponics
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