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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 North America. It is also called “measuring worm” of “inchworm”. It walks by arching its body, then stretching out and grasping the branch with its front feet, then looping its body again to bring the hind feet forward. When danger threatens, the stick caterpillar stretches its body away from the branch at an angle and remains rigid and still, like a twig, until the danger has passed.

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. By changing the color of its skin

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

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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”

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