时间:2019-02-24 作者:英语课 分类:英语听力文摘 English Digest


英语课

  Some methods of preserving food are easy to understand.

For example, it's easy to see that freezing your food, or packing it in salt, would make it inhospitable to the microbes which would otherwise cause it to spoil. You might wonder, however, about jams, jellies, and preserves, all of which are protected from spoiling by a high concentration of sugar. Sugar is one of the most basic foods for all life--bacteria and mold like to eat it just as much as we do. On today's Moment of Science we'll learn how too much of a good thing can be deadly, at least for microorganisms.

Sugar works not by poisoning the food-spoiling microbes, but by causing them to literally 1 die of thirst.

This is because sugar attracts water very well; the more sugar there is in any solution, the more water it tries to draw from its surroundings. This is bad news for any microbe that happens to be inside a jar of jam. High concentrations of sugar will suck the microbe's vital water right through its cell wall, causing it to dehydrate 2. This process is called "osmosis," and it can be deadly for bacteria and mold.

In order for osmosis to work, the sugar concentration has to be quite high. If any water falls onto the surface of your jam, the sugar concentration at that spot might become low enough to allow mold to grow. That's why it's important to take the back up measure of refrigerating all jams, jellies, and preserves once you've opened them. Like an oasis 3 in the desert, condensed water dripping from the jar's lid can give a dehydrating microbe the relief it needs.



adv.照字面意义,逐字地;确实
  • He translated the passage literally.他逐字逐句地翻译这段文字。
  • Sometimes she would not sit down till she was literally faint.有时候,她不走到真正要昏厥了,决不肯坐下来。
vt.使脱水
  • People can very quickly dehydrate in the desert.人在沙漠里很快就会脱水。
  • Without these structures, many warm-blooded animals would quickly dehydrate,especially in dry climates.没有这样的结构,许多温血动物将很快脱水,特别是在干燥的气候条件下。
n.(沙漠中的)绿洲,宜人的地方
  • They stopped for the night at an oasis.他们在沙漠中的绿洲停下来过夜。
  • The town was an oasis of prosperity in a desert of poverty.该镇是贫穷荒漠中的一块繁荣的“绿洲”。
学英语单词
a (axial)
accelerator partus
areolar central choroiditis
articulate brachiopods
aurochromoderma
auto-hemolysis test
Banifing
bescorned
Bezau
biocalc
boiler feed water compound pump
bourdis
chemical addition agent
chemical runoff
child art
Cirrphyllum
color shape
comparison analysis method
cooling time
counterionic
cutaneous autoplasty
declared working condition
diazatrophic
diphalangia
direct style
discloser
distance gauge for sleepers
Doc-in-a-Box, doc-in-a-box
dortry
ectopeptidase
equivalent concentration
essentials of general average
field chopper
flip chip structure
fluororubber 26
Freewood Acres
give oneself airs
go out of existence
Goodyera viridiflora
green-stain
grimsels
Hankasalmi
herpes virus
hobit
home-remedy
hydrate form
insulated oiling pole
invariance theorem
jeblet
Kaldo
Khābāspur
korbecki
kuaua
low frequency electric induction furnace
Mantala
mean bore diameter variation
muskewashe
mutual induction electromotive force
neuropodous
nonspectacular
norovirus
noroviruss
North Muiron I.
oil reservoir screen
omah
orthokeratin
Oxford Junction
part in bending
path sensitization
perdu
Picardy
pink-handed
planned outage time
plano-aspheric corrector
platitudinised
positioning accuracy-fine
post-knight
postillation
preoxygenation
provincial government building
radar rangefinder
ramsgill
rate cap
reciprocation compressor
Rhaponticum
ribbon powder
scrubbe
sharpen
software used
sting-out
stohr
stopmeter
superficies inferia
supervolcanos
the number of times
thoracicohumeral
thromboblast
torpedo net
unconscionably
upper steam cylinder gasket
water hens
yoffie