雅思阅读第079套P2-The race to make spider silk
Reading Passage 2
You should spend about 20minutes on Questions 15-27 which are based on this passage.
The race to make spider silk
The strength, toughness, andelasticity of silk continue to fascinate scientists, who wonder what gives thisnatural material its unusual qualities. Finer than human hair, lighter thancotton, and ounce for ounce stronger than steel, silk is of special interest tomaterials researchers. They are trying to duplicate its properties andsynthesise it for large-scale production. Silk holds the promise ofwear-resistant shoes and clothes; stronger ropes, nets, seatbelts andparachutes; rustfree panels and bumpers for automobiles; improved sutures andbandages; artificial tendons and ligaments; supports for weakened blood vesselsas well as bulletproof vests.
Many insects secrete silks ofvarying quality. Best known is the moth bombyx mori, whose caterpillar iscommonly known as the silkworm. It spins its cocoon from a single threadbetween 300 and 900 metres long and has been used for centuries to make finegarments. But the focus of scientific attention today is on spider silk:tougher, stretchier, and more waterproof than silkworm strands. Spiders make asmany as seven different types of silk, but one spider and two types of silk areat the centre of intense interest. The spider is the golden orb-weaving spider,nephila clavipes. Its two silks under investigation go by the evocative names'dragline’ and 'capture’.
Dragline is the silk whichforms the frame for the wheel-shaped webs and enables the dangling spider todrop down and grab its prey. This silk exhibits a combination of strength andtoughness unmatched by high-performance synthetic fibre.
Capture silk is the resilientsubstance at the centre of the web. To catch a speeding insect, it may stretchto almost three times its original length. Insects get entangled in the stickyweb because the stretchiness of capture silk lets the web move back and forthafter the insect hits it. If the web were stiff, the insect might just bounceoff. Whereas dragline is stronger, capture silk is more flexible, five timesmore flexible in fact.
Because the orb weaver’ssurvival depends on its silk, some 400 million years of evolution have fine-tuneda remarkably tough and versatile material. Now, research groups all over theworld are competing to spin the first artificial spider silk, a job thatrequires a three-step approach: to determine the fibre’s moleculararchitecture, to understand the genes that yield silk proteins, and then tolearn how to spin the raw material into threads.
The first two steps are wellunderway. The molecular structure for both dragline and capture silk is knownand now researchers have cloned several genes for the silks and unravelledtheir protein structure.
The next step is to find hostsfor the artificial genes. Plants and fungi, as well as bacteria, are beingconsidered. If a hardy plant could express a dragline silk gene, silk proteinscould eventually be harvested in large quantities, processed into a liquid,polymer, and spun in factories, A different experimental approach is to insertthe web gene into goats in order to collect the protein from the goats’ milk.Goats are being used instead of the simpler and much cheaper bacteria, becausethe secret of the protein’s strength lies in how the molecules cross-link withone another. When bacteria is used to make artificial web, the protein folds ina way that prevents it. from cross-linking properly, resulting in hard whilelumps. The spider makes protein in a manner similar to the way mammals makemilk, so the researchers hope that the protein made in the goats’ mammaryglands will be able to cross-link properly. Once the protein is extracted fromthe goats’ milk, the next step is to find a way to spin it.
Spiders make their silk inenvironmentally friendly ways. They process proteins from water-based solutionswhich, from a manufacturing point of view, is very attractive. The process ofmaking synthetic fibres like nylon, on the other hand, requires petroleumproducts or organic solvents and results in pollution. So bio-technologists arcmotivated by both the practical and economic potential of generating artificialspider silk. Globally, as much as 60 per cent of the threads used to weaveclothing come from natural fibre, including cotton, wool, and silk. The aim isto offer substitutes for natural fibres that arc free of the problems of poorwash-wear performance: stretching, wrinkling arid shrinkage. They are seeking abetter-than-natural alternative fibre for which there is a major market.Bio-inspired materials are providing a new frontier for the fibre business.
SECTION 2: QUESTIONS 15-27
Questions 15-19
Classify the following asrelating to:
A
the silk of bombyx mori
B
dragline silk of nephila clavipes
C
capture silk of nephila clavipes
EXAMPLE
ANSWER
forms the cocoon
A
15 __________forms the framework of a web
16 __________most elastic silk
17 __________allows predator to drop quickly
18 __________single strand can be up to 900 metres long
19 __________strongest silk
Questions 20-24
Do the following statementsreflect the claims of the writer in the passage?
Write:
YES
if the statement agrees with the views of the writer
NO
if the statement contradicts the views of the writer
NOT GIVEN
if it is impossible to say what the writer thinks about this
20 _________________ All spiders secrete silk.
21 _________________ Artificial genes for spider silk have been produced.
22 _________________ Spider silk protein occurs naturally in goats’ milk.
23 _________________ China is leading research efforts in the area of spider silk.
24 _________________ Spider silk is now being produced commercially.
Questions 25-27
Using NO MORE THAN THREEWORDS from the passage for each answer, complete the following.
Comparison of Synthetic and Natural Fibres
· Main problem in the production of synthetic fibres:
25 _________________
· 3 disadvantages of natural fibres:
26 _________________
· Proportion of clothing made from natural fibre:
27 _________________
