跳转到主要内容
IELTS Mock Test 2024 February

IELTS Mock Test 2024 February

3.3
(1,550 评分人数)
  • 发布时间: 07 Sep 2023
  • 模考人次: 1,466,361

正确答案:

Part 1: Question 1 - 14
  • 1 E
  • 2 H
  • 3 C
  • 4 B
  • 5 B
  • 6 FALSE
  • 7 TRUE
  • 8 NOT GIVEN
  • 9 FALSE
  • 10 TRUE
  • 11 D
  • 12 E
  • 13 B
  • 14 C
Part 2: Question 15 - 27
  • 15 B
  • 16 B
  • 17 A
  • 18 A
  • 19 C
  • 20 B
  • 21 A
  • 22 C
  • 23 E
  • 24 D
  • 25 FALSE
  • 26 TRUE
  • 27 TRUE
Part 3: Question 28 - 40
  • 28 ii
  • 29 v
  • 30 i
  • 31 iv
  • 32 viii
  • 33 insects
  • 34 nectar
  • 35 one third
  • 36 cross-pollination
  • 37 energy costs
  • 38 tree species
  • 39 trap-lining
  • 40 A
提高雅思成绩的小贴士
剑桥雅思12听力原文-TEST8

剑桥雅思12听力原文-TEST8

3.8
(6 评分人数)
619
25 Oct 2023

详细试卷答案解析:

Part 1: Questions 1-14

Questions 1-5

Questions 6-10

Questions 11-14

READING PASSAGE 1

You should spend about 20 minutes on Questions 1-14, which are based on Reading Passage 1 below.

Relish the flavour - how the brain perceives flavour

A. The terms “taste” and “flavour” are used interchangeably. Strictly speaking, however, taste refers to five basic qualities: salty, sour, sweet, bitter and umami (a characteristic of protein-rich foods such as meat and cheese). Smell plays an equally prominent role in flavour but is often underappreciated. Try holding your nose and popping a strawberry- flavoured sweet in your mouth. You will taste the sweetness, but not the strawberry until you let go of your nose and the volatile chemicals from the confectionery enter the nostrils. As if that were not complex enough, irritants—for example, carbonation or the coolness of mint—are detected not by taste or smell, but by the trigeminal sense, a part of the touch system adapted for the mouth. The brain receives news about what is in the mouth from receptors—proteins specialised in picking up particular molecules—located throughout the oral and nasal cavities. Receptors for smell were identified in the early 1990s, and for sweet, bitter and umami only in the past two years (sour and salty tastes were somewhat better understood). That, says Gary Beauchamp, director of the Monell Chemical Senses Institute in Philadelphia, whose group contributed to some of the findings, is more than has been learnt about taste in the past 2,000 years. A receptor for capsaicin, the molecule that gives chilli peppers their bite, was identified only in 1997.

B. The discovery of taste receptors opens the way to mimicking, enhancing or blocking  them  for  various  desired  effects—such  as  increasing  the  salty taste  of  low-sodium  foods,  or  preventing  the  bitterness  that  characterises many  medicinal  drugs,  or  boosting  the  flavours  of  diets  for  the  elderly  to ensure they eat properly. But receptors are only part of the story. Nobody knows how the brain distinguishes a mouthful of milk from a bite of bread, or  chicken  tikka  masala  in  an  Indian  restaurant  from  one  bought  at  a supermarket.  Although  some  scientists argue  that the  brain's response  to stimuli  is  a  simple  map  of  the  receptors  in  the  tongue  and  nose,  a  more compelling  theory  suggests  that  the  overall  patterning  of  signals  together creates a sense of particular flavours, whose attractiveness is judged in the light of previous experience. 

There are no useful algorithms to measure brain inputs and outputs against subjective  reports  of  flavour  sensations.  That  is  good  news  for neurophysiologists  looking  for  work.  But  for  flavour  and  fragrance companies—with global sales of flavours accounting for more than a third of  the  $35  billion-a-year  food  ingredients  market—acceptable  tastes  bear directly  on  the  bottom  line.  There  is  no  question  that  flavour  is  the  most important  criterion  for  consumer  acceptance  of  foods.  And  being  able  to predict what customers will like is the industry's greatest single ambition.

C. Throughout history, flavours have been coveted for their ability to increase the palatability of food  and to  enliven cuisine. In 408, Alaric the  Visigoth's price  for  raising  the  siege  of  Rome  allegedly  included  more  than  1,000 kilograms of pepper. Industrial production of perfumes began in France in the 18th century to take the smell out of leather gloves. The flavour industry was  a logical consequence  of such developments.  Extracts  and  essential oils  such  as  citrus  were  being produced in America  by  the  late  1700s.  In 1874,  Haarmann  and  Reimer  in  Germany  became  the  first  company  to make synthetic vanillin (from the sap of conifers) on an industrial scale. At first, isolating and identifying gustatory ingredients proved extremely hard. Not  only  were  analytical  methods  rudimentary,  but  the  substances responsible  for  taste  are  present  in  minuscule  amounts  even  in concentrated foods such as crushed raspberries. After 1950, new analytical techniques  made  it  possible  to  detect  trace  ingredients,  and  companies accumulated  chemical  libraries  that  today  contain  thousands  of compounds. 

D. Depending  on  what a customer wants, flavours can be used off  the shelf, modified  or  created  anew,  following  a  principle  called GRAS (generally recognised  as  safe).  It  is  a  constant  challenge  to  be  unique,  says  Bob Eilerman,  leader  of  flavour  research  and  development  for  Givaudan,  a Swiss  company  whose  scientists  float  over  tropical  rainforests  in  hot-air balloons  to find  new  tastes and ingredients, capture  their aromas on  site, and  then  analyse  and  re-create  them  in  the  laboratory.  The  most  potent flavoured  chemicals  are  created  by  cooking,  says  Anthony  Blake,  vice-president  of  food  science  and  technology  at  Firmenich  in  Geneva. Firmenich,  Givaudan  and  International  Flavours  and  Fragrances,  the industry leader in America, comprise the big three of flavour and fragrance companies world-wide. Small wonder that Firmenich employs techno-chefs, or that Givaudan dispatches analysts to ethnic restaurants hither and yon.

E. Like  colourists  grinding  and  mixing  pigments,  professional  flavourists assemble  the  50-100  components  that  are  typical  for  a  flavour  into  the finished  product.  Acceptability  is  measured  using  panels  of  expert  and consumer  (ie,  naive)  taste-testers  in  a  process  called  sensory  analysis. Trained  testers  might  be  asked  to  rate  the  taste  of  vanilla  ice-cream according  to  standards  for  sweetness  and  vanilla  flavour,  whereas consumer  testers  simply  register  whether  they  like  it.  The  process  is  an iterative  one,  with  several  rounds  of  refinement  between  testers  and flavourists, until the product is deemed to have an acceptable taste. 

Unfortunately,  says  Alex  Häusler,  director  of  flavour  excellence  at Givaudan, while humans provide the most sensitive testing instrument, they are  not  the  most  reliable.  People  are  born  with  different  sets  of  taste receptors and different ways of interpreting them. Think of the last time you watched somebody pour spoonfuls of sugar into a cup of coffee. Texture is a  particular  conundrum.  It  contributes  substantially  to  the  pleasure  of eating, yet very little is known about it. Why is rubbery squid enjoyable and rubbery toast not? What does “succulent” mean? Since the 1960s, the food industry  has  devised  a  battery  of  instrument  tests  for  desired  textural properties, including poking peas with pins and bending biscuits. But theory has been  lacking, and giving a carrot  a  whack bears little resemblance to what  happens  inside  the  mouth,  where  it  is  traversed  by  a  multitude  of physicochemical  processes.  Julian  Vincent  of  the  University  of  Bath,  in Britain, is one of  a small  band of academic researchers who are  trying to relate the results of mechanical tests to perceptions such as crispness. 

F. The dynamics of flavour release—ie, the appearance and disappearance of flavour—have also resisted measurement. Researchers at the University of Nottingham,  also  in  Britain,  have  developed  and  commercialised  an instrument called MS-Nose that sucks in breath from a person's nose while they are chewing gum, for instance, and  analyses the aroma molecules it finds  there.  Firmenich has  adopted  the technology in  its  search for better ways  of  delivering  flavour.  The  approach  has  stimulated  a  good  deal  of interest, even though the results tend to be unique to the person tested. 

Physiological  studies  of  flavour  are  conducted  using  animals  (mostly  rats and hamsters) or bacteria, which have robust taste receptors.  In humans, techniques  such  as  functional  magnetic-resonance  imaging  and  positron-emission  tomography—currently  being  applied  to  problems  as  diverse  as working memory and lovesickness—can reveal patterns of electrical activity swishing around the brain in real time, says Dr Blake. The idea is to get a person to eat something and see what parts of their brain light up. But the technologies  are  not  yet  sensitive  enough,  nor  are  the  ways  of  analysing the  data  meaningful  enough,  for  the  methods  to  be  useful  in  studies  of flavour. An alternative approach, says Monell's Dr Beauchamp, would be to focus  on  specific  genes  in  animals  and  alter  them  to  track  the  pathways that the brain uses in integrating signals from the receptors.

G. At present, finding the right enhancer or blocker for a given receptor means looking  at  thousands  of  compounds,  a  task  better  suited  to  automated testing than the caprices of the human tongue. Senomyx, a young biotech company  in  La  Jolla,  California,  intends  to  use such  a  technology,  called “high-throughput  screening”,  to  test  legions  of  compounds  against  taste and smell receptors. Whether the technique will  prove more successful in food science than in pharmaceutical research and development, where it is widely  used  but  has  not  yet  produced  a  blockbuster  drug,  remains  to  be seen.  Another  biotech  firm,  Linguagen  of  Paramus,  New  Jersey,  is  also bringing  modern  science  to  bear  in  the  search  for  flavour  modifiers, particularly bitterness blockers.

H. The mouth is the portal of entry to the gut, and taste is the final arbiter. Innate aversions to sour and bitter substances—caffeine, nicotine, strychnine, for example—and a liking for sweet and salty ones reflect the wise choices that humanity's ancestors made in a hostile environment. Beyond these protective and nutritional reflexes, however, taste preferences are largely a matter of culture and learning. The taste system is reasonably compliant, says Tom Scott, a neurophysiologist and dean of sciences at San Diego State University in California. Cultures are kept distinct by cuisines, and cuisines are distinguished by taste. 

But cuisines, like continents, have a habit of colliding. Ten years ago, few Americans cared for raw fish. Now they eat sushi almost as avidly as the Japanese. Moreover, “acquired tastes” often involve complex contradictions that play tricks within the brain. How else do you explain the liking for strong-smelling cheese or the East Asian fruit called durian that is so redolent of vomit that it is banned on public transport in some countries? Other effects resist reconciliation, like the unbearable sweetness that artichokes lend to wine. Flavour appears to belong to a family of subtle perceptions—such as recognising a voice or telling faces apart. But how does the central nervous system process all the information needed to make these fine-grained distinctions? The answer should help to develop cheaper and safer flavour compounds, as well as to perform tricks of alchemy such as turning tofu into steak. More fundamentally, identifying algorithms in the brain that transform taste into flavour, and comparing them with how people process complex sounds or tactile sensations, might reveal something about how perception really works.

有话要说:

Notifications
您的信息