The livelihood of each species in the
vast and intricate assemblage of living things depends on the existence of other
organisms. This interdependence is sometimes subtle, some times obvious. Perhaps
the most straightforward dependence of one species on another occurs with
parasites, organisms that live on or in other living things and derive nutrients
directly from them. The parasitic way of life is widespread. A multitude of
microorganisms (including viruses and bacteria) and an army of invertebrates or
creatures lacking a spinal column (including crustaceans, insects, and many
different types of worms) make their livings directly at the expense of other
creatures. In the face of this onslaught, living things have evolved a variety
of defense mechanisms for protecting their bodies from invasion by other
organisms. Certain fungi and even some kinds of bacteria
secrete substances known as antibiotics into their external environment. These
substances are capable of killing or inhibiting the growth of various kinds of
bacteria that also occupy the area, thereby eliminating or reducing the
competition for nutrients. The same principle is used in defense against
invaders in other groups of organisms. For example, when attacked by
disease-causing fungi or bacteria, many kinds of plants produce chemicals that
help to ward off the invaders. Members of the animal kingdom
have developed a variety of defense mechanisms for dealing with parasites.
Although these mechanisms vary considerably, all major groups of animals are
capable of detecting and reacting to the presence of "foreign" cells. In fact,
throughout the animal kingdom from sponges to certain types of worms shellfish,
and all vertebrates (creatures possessing spinal column) , there is evidence
that transplants of cells or fragments of tissues into an animal are accepted
only if they come from genetically compatible or closely related
individuals. The ability to distinguish between "self" and
"non-self", while present in all animals, is most efficient among vertebrates,
which have developed an immune system as their defense mechanism. The immune
system recognizes and takes action against foreign invaders and transplanted
tissues that are treated as foreign cells.
单选题
What does the passage mainly discuss?
A. How parasites reproduce.
B. How organisms react to invaders.
C. How antibiotics work to cure disease.
D. How the immune system of vertebrates developed.
【正确答案】
B
【答案解析】[解析] 本文主要讨论有机体如何防御其他生命体的入侵。
单选题
The word "intricate" in line 1 is closest in meaning to ______.
A. difficult
B. widespread
C. critical
D. complex
【正确答案】
D
【答案解析】[解析] 分析这个句子可知“intricate”与“vast”并列来修饰“assemblage of living things”。difficult“困难的”，widespread“广泛的”和critical“关键的”均不合适。揣测作者意图，可知complex“复杂的”符合题意，译为“浩瀚复杂的生命集合”。
单选题
According to the passage, some organisms produce antibiotics in order
to ______.
A. prevent disease in humans
B. aid digestion
C. fight off other organism
D. create new types of nutrients
【正确答案】
C
【答案解析】[解析] 本题的设题点在第二段。根据第二段第二句“These substances are capable of killing or inhibiting the growth of various kinds of bacteria that also occupy the area, thereby eliminating or reducing the competition for nutrients.”可知，抗生素能够杀死或抑制其他不同菌类的生长。
单选题
According to the passage, a transplant of tissue between genetically
incompatible organisms will result in the transplanted tissue ______.