单选题
{{B}}Lichens{{/B}}
To be certain, a lichen is not the most conspicuous of plants. Lichens grow in unassuming fashion on rocks, logs and other exposed surfaces in a wide range of habitats around the world. To the untrained eye they look like little more than crusty patches that, at first glance, might easily be mistaken for a discoloration of the surface. Even if the average person should happen to notice the lichen's presence and correctly identify it as some form of life, he is unlikely to go much further in contemplating it. Though almost totally ignored by the layperson, for the botanist, lichens are one of the most fascinating of all plants, and one of the most intensely studied.
They are the subject of so much scientific scrutiny primarily because a lichen is not just one plant. It is, in fact, a composite organism made up of fungus and algae living together in a close association that is, presumably, beneficial to both. When these two very different plants combine, the result is a unique and very long-lived composite organism that appears, at least on a macroscopic scale, to be a unitary plant. It is an organism that bears no resemblance to either of its constituents when they are observed individually. The separate fungal and alga) elements can be recognized only when the body of the plant, called a thallus because there are no stems or roots, is sectioned and examined under a microscope. When viewed this way, the fungus component dominates the picture, as it accounts for nine tenths of the total body mass of the lichen. But, entrapped within it, clearly visible as dark spots, are the algae cells. Essentially, nothing is known of how an amorphous mass of fungi and algae come together to form a highly differentiated, structurally stable body.
Despite all the scientific scrutiny lichens have
received, it is still not entirely certain what each member gains from the
association. 
Some researchers have speculated
that the fungi join in the relationship because they are able to consume the
algae cells as they die and therefore are guaranteed a food supply. 
It is well-known that the chlorophyll-containing
algae cells produce food by means of photosynthesis. 
To be certain, a lichen is not the most conspicuous of plants. Lichens grow in unassuming fashion on rocks, logs and other exposed surfaces in a wide range of habitats around the world. To the untrained eye they look like little more than crusty patches that, at first glance, might easily be mistaken for a discoloration of the surface. Even if the average person should happen to notice the lichen's presence and correctly identify it as some form of life, he is unlikely to go much further in contemplating it. Though almost totally ignored by the layperson, for the botanist, lichens are one of the most fascinating of all plants, and one of the most intensely studied.
They are the subject of so much scientific scrutiny primarily because a lichen is not just one plant. It is, in fact, a composite organism made up of fungus and algae living together in a close association that is, presumably, beneficial to both. When these two very different plants combine, the result is a unique and very long-lived composite organism that appears, at least on a macroscopic scale, to be a unitary plant. It is an organism that bears no resemblance to either of its constituents when they are observed individually. The separate fungal and alga) elements can be recognized only when the body of the plant, called a thallus because there are no stems or roots, is sectioned and examined under a microscope. When viewed this way, the fungus component dominates the picture, as it accounts for nine tenths of the total body mass of the lichen. But, entrapped within it, clearly visible as dark spots, are the algae cells. Essentially, nothing is known of how an amorphous mass of fungi and algae come together to form a highly differentiated, structurally stable body.
Despite all the scientific scrutiny lichens have
received, it is still not entirely certain what each member gains from the
association. Some researchers have speculated
that the fungi join in the relationship because they are able to consume the
algae cells as they die and therefore are guaranteed a food supply. It is well-known that the chlorophyll-containing
algae cells produce food by means of photosynthesis.
单选题
According to paragraph 1 of the passage, which of the following
statements is true?
【正确答案】
B
【答案解析】
单选题
The word scrutiny in paragraph 2 is closes in meaning to
【正确答案】
A
【答案解析】
单选题
The word amorphous in paragraph 2 is closest in meaning to
【正确答案】
D
【答案解析】
单选题
According to the passage, how might the fungus benefit from its
association with algae?
【正确答案】
B
【答案解析】
单选题
Which of the following question is addressed in paragraph 3
of the passage?
【正确答案】
C
【答案解析】
单选题
The word retention in paragraph 3 is closest in meaning to
【正确答案】
B
【答案解析】
单选题
What is main function of paragraph 4?
【正确答案】
A
【答案解析】
单选题
Which of the following if proven true would do most to clarify how
fungus benefits from its association with algae?
【正确答案】
A
【答案解析】
单选题
The word susceptible in paragraph 5 is closest in meaning to
【正确答案】
B
【答案解析】
单选题
Which is of the following is implied in paragraph 5 of the passage?
【正确答案】
C
【答案解析】
单选题
Look at the four squares [■] that indicate where the following
sentence could be added to the passage.
{{B}}Such a relationship does not develop in biology unless it benefits at least one of the members.{{/B}}
Where would the sentence best fit?
{{B}}Such a relationship does not develop in biology unless it benefits at least one of the members.{{/B}}
Where would the sentence best fit?
【正确答案】
B
【答案解析】