2014年6月21日托福阅读真题P2+题目+答案：Metamorphosis

2014年6月21日托福阅读真题P2+题目+答案：Metamorphosis

Organisms that metamorphose undergo radical changes over the course of their life cycle. A frog egg hatches a tadpole that metamorphoses into an adult frog within a few days or weeks. A fruit fly egg hatches a larva that feeds for a few hours or days and then enters the pupal stage during which it develops a protective covering. The changes that occur during the metamorphosis of a single species may be so great that the species occupies two separate and very different niches or places in an environment at different times. In fact, the larvae of two species may be more similar to each other than to the corresponding adult forms of their own species.

1. The word “radical” in the passage is closest in meaning to

A.extreme

B.distinctive

C.periodic

D.structural

2. According to paragraph 1, which of the following is true of the organisms that become fruit flies?

A.They feed during the pupal stage.

B.They become winged insects several days after the larvae hatch from eggs.

C.They remain in the larval stage longer than they remain in the pupal stage.

D.They need to be protected during the larval stage in order to reach the pupal stage.

Organisms that utilize different resources at different stages of their life cycle face an unusual evolutionary problem, exploiting different niches may be difficult with a single body plan. The solution is a juvenile (immature) form specialized for one niche, followed by metamorphosis to an entirely new body plan, adapted to a different niche in the adult. Clearly, species that metamorphose must undertake complex genetic and physiological processes in the transformation. These changes require complex regulatory mechanisms that involve turning on and off many genes at appropriate times. In addition, the reorganization of the body plan in a metamorphic species entails considerable energy costs. What sorts of ecological advantages could outweigh these complications?

3. It can be inferred from paragraph 2 that an advantage of

A.develop regulatory mechanisms for turning genes on and off

B.occupy different niches at different parts of the life cycle

C.undertake complex genetic and physiological processes

D.reduce their energy costs

4. Why does the author ask the question “What sorts of ecological advantages could outweigh these complications?”

A.To suggest that there is no single advantage but many advantages

B.To challenge the idea that metamorphic transformations are always beneficial

C.To prepare readers for a discussion that may explain why metamorphosis occurs

D.To identify a particular aspect of metamorphosis that is poorly understood

One prevailing hypothesis is that metamorphic species specialize so as to exploit habitats with high but transient (short term) productivity----and hence high potential for growth. Part of this strategy is that specializations for feeding, dispersal, and reproduction are separated across stages. A frog tadpole occupies an aquatic environment (such as a pond) with extremely high potential for growth. The existence of the pond or its high production may be transient, however. Whereas an aquatic larva is not capable of dispersal to new ponds if its habitat becomes unsuitable, the adult frog is. In this case rapid growth in the larva is separated from dispersal and reproduction in the adult. Although the adult feeds, its growth rate is far less than that of the tadpole. The energy adults obtain from feeding is dedicated to dispersal and reproduction.

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