Insects´ lives are very short and they have many enemies, but they must survive long enough to breed and perpetuate their kind. The less insect like they look, the better their chance of survival. To look “inedible” by resembling or imitating plants, is a deception widely practiced by insects. Mammals rarely use this type of camouflage, but many fishes and invertebrates do.
The stick caterpillar is well named. It is hardly distinguishable from a brown or green twig. This caterpillar is quite common and can be found almost anywhere in
Walkingsticks, or stick insects, do not have to assume a rigid, twiglike pose to find protection, they look like inedible twigs in any position. There are many kinds of walkingsticks, ranging in size from the few inches of the North American variety to some tropical species that may be over a foot long. When at rest their front legs are stretched out. Some of the tropical species are adorned with spines or ridges, imitating the thorny bushes or trees in which they live.
Leaves also seem to be a favorite object for insects to imitate. Many butter flies can suddenly disappear from view by folding their wings and sitting quietly among the foliage that they resemble.
1. What is the main subject of the passage?
A. Catepillars that live in trees
B. The feeding habits of insects
C. How some insects camouflage themselves
D. Insects that are threatened with extinction
2. In lines 1, the word “enemies” refers to.
A. other creatures competing for space
B. extreme weather conditions
C. creatures that eat insects
D. inedible insects
3. According to the passage, how does the stick caterpillar make itself look like a twig?
A. By holding its body stiff and motionless
B. By looping itself around a stick
C.
D. By laying its body flat against a branch
4. Which of the following is true of stick insects?
A. They resemble their surroundings all the time.
B. They make themselves look like other insects.
C. They are camouflaged only when walking.
D. They change color to make themselves invisible.
5. Which of the following are not mentioned in the passage as objects that are imitated as a means of protection?
A. Thorns B. Flowers C. Leaves D. Sticks
6.In which paragraph does the author describe the way in which stick caterpillars move?
A. Paragraph one B. Paragraph two
C. Paragraph three D. Paragraph four
Enzymes are often used as nonrecoverable chemical reagents, in which case they are added to the substrate incubated at the required temperature and pH for a period and subsequently destroyed. Amylase, proteases and other inexpensive bulk enzymes are used in this way. Alternatively, enzymes may be attached to an inert support (immobilized). This offers the advantages of (1) recovery and re-use of the enzymes, in batch reactors; or (2) the development of continuously operated enzyme reactions similar to continuous fermentation systems used for microorganisms; (3) the possibility of multi-enzyme systems; and (4) the enzyme does not remain in the processed solution. However, there are some disadvantages, the enzyme may be stabilized by immobilization but it may also lose activity, and the process becomes technically more complex.
There are many ways to immobilize enzymes, the common procedures involve (1)absorption to an insoluble support of either organic or inorganic origin. Cellulose, dextran, nylon and bentonite are some of the many carriers that have been used. Attachment may be by physical adsorption, ionic binding or covalent bonding. (2) Entrapment methods in which the enzyme is localized within a polymer matrix are popular and include gel or fiber entrapment and microencapsulation in which the enzyme is enclosed within sperical semipermeable polymer membranes. (3) A simple but effective procedure is to immobilize the enzyme within the host cell by heat treatment or covalent cross-linking following by pelleting the cells.
Are the following statements true or false?
（1）Amylase, proteases and other inexpensive bulk enzymes are destroyed after the enzyme-catalyzed reaction is completed
（2）The advantages of immobilization of the enzymes include the stability of the enzymes and the increase of the enzyme activity
（3）By immobilization of the enzymes, it is possible to operate the enzyme reactions continuously
（4）In the last paragraph, the word “insoluble support” has the same meaning as the word “carrier”
Biosynthetic metabolic pathways often have a common enzyme sequence and then branch leading to more than one end-product. Microorganisms have evolved feedback mechanisms, whereby a build-up of one end-product cause a feedback effect on the first enzyme of the branch leading to that product. In addition, mechanisms exist whereby the end-product of a branched pathway causes partial feedback inhibition of the first enzymes of the common sequence so that the flux of substrate passing through this sequence is proportionately reduced. This effect is achieved by use of isoenzymes, concerted feedback regulation and cumulative feedback regulation. These regulatory effect can be of two types: inhibition of enzyme activity and repression of enzyme synthesis. Where isoenzymes (multiple enzyme forms capable of catalysing the same reaction) are involved, the synthesis or inhibition of each enzyme form may be regulated by a different end-product. With concerted feedback regulation, only one enzyme is involved, but more than one product must be present to inhibit activity or repress enzyme synthesis. With cumulative feedback regulation, each end-product causes partial inhibition or repression and all end-products are required to completely block activity or synthesis.
1. In the first sentence, ‘a common enzyme sequence’ means:
(1) the reaction sequence catalysed by the enzymes
(2) that the enzyme has the same amino acids sequence
2.In concerted feedback regulation the enzyme is inhibited and repressed by
(1) several kinds of end-products
(2) only one kind of end-product
3. The isoenzymes means:
(1) the enzymes have different functions
(2) the enzymes are capable of catalysing the same reaction
4. With cumulative feedback regulation, each end-product causes:
(1) complete inhibition and repression
(2) partial inhibition or repression
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Lichens grow in almost every natural habitat imaginable, from deserts to tropical rain forests—even on the back of certain beetles in New Guinea and inside rocks(along with algae) in the otherwise barren dry valleys of Antarctica.
Many species can not tolerate extreme heat, cold or dryness. Very few, however, can survive heavy air pollution, and many live only where the air is very clean. The disappearance of lichens from an area gives warning of a threatened environment.
1. Which of the following would be the best title for the passage?
A. The versatility and complexity of the lowly lichen
B. The hidden characteristics of algae colonies
C. The disappearance of the lichen species
D. The habitats of spectacular fungi
2. The author states that lichens grow “as though designed to be ignored” because they are
A. not totally understood by botanists
B. troublesome to collect for the purposes of study
C. uncomplicated in their internal structure
D. not easily noticed by observers
3. According to the author, most people are unaware that lichen is a.
A. leafy plant
B. class of simple bacteria
C. two-dimensional life form
D. Combination of organisms
4. The “unique” compounds mentioned in the second paragraph are produced.
A. through the cooperative efforts of the lichen’s parts
B. only under laboratory conditions
C. through one of the three possible processes
D. once in the lichen’s life cycle
5. The author implies that lichens might be used to.
A. find water sources
B. destroy unwanted plant life
C. test for air purity
D. provide food in remote areas
