Passage One
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, sometimes 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 environm
A. How parasites reproduce.
B. How organisms react to invaders.
C. How antibiotics work to cure disease.
D. How the immune system of vertebrates develope
Passage One
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, sometimes 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 environm
A. difficult
B. widespread
C. critical
D. complex
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