TPO13-2Biological Clocks 生物钟
本篇稍难：全文共三段，因而段长题多;个别句子晦涩难解。但稍花时间细致分析也会收获颇丰!
1. Normally, the constantly changing levels of an animal'sactivity—sleeping, feeding, moving, reproducing, metabolizing, and producing enzymes and hormones, for example—are well coordinated with environmental rhythms, but the key question is whether the animal's schedule is driven by external cues, such as sunrise or sunset, or is instead dependent somehow on internal timers that themselves generate the observed biological rhythms.
2. Byisolating organisms completely from external periodic cues, biologists learned that organisms have internal clocks. For instance, apparently normal daily periods of biological activity were maintained for about a week by the fungus Neurospora when it was intentionally isolated from all geophysical timing cues while orbiting in a space shuttle.(修辞目的题：观点+论据)
3. Indeed, stability of the biological clock's period is one of its major features, even when the organism's environment is subjected to considerable changes in factors, such astemperature, that would be expected to affect biological activity strongly.(句子简化题：evenwhen表让步)
4. As a result, its activities are shifted relative to the external cycle of the new environment. The disorienting effects of this mismatch between external time cues and internal schedules may persist, like our jet lag, for several days or weeks until certain cues such as the daylight/darkness cyclereset the organism's clock to synchronize with the daily rhythm of the new environment.(因果关系：事实信息题考点。)
5. Such an external cue not only coordinates an animal's daily rhythms with particular features of the local solar day but also—because it normally does so day after day-seems to keep the internal clock's period close to that of Earth's rotation.(正确理解指代才能准确翻译。)
6. Yet despite this synchronization of the period of the internal cycle, the animal's timer itself continues to have its own genetically built-in period close to, but different from, 24hours. Without the external cue, the difference accumulates and so theinternally regulated activities of the biological day drift continuously, like the tides, in relation to the solar day.(不要让插入语切断对句子的完整理解。)
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