2022年自考《英语（二）》模拟题29

Can staying up late make you fat?A growing body of research has suggested that poor sleep quality is linked to an increased risk of obesity(肥胖症).But a new study found that it’s not the sleep loss that leads to obesity,but rather that overweight can cause poor sleep.The researchers discovered their findings in a very small worm,called C．elegans.

Study co-author David Raizen stressed that while these findings in worms may not translate directly to humans,C．elegans offers a good model for studying humans'sleep.Like all other animals that have nervous systems,they need sleep.But unlike humans,who have complex neural circuitry(神经回路)and are difficult to study,a C．elegans has only 302 nerve cells，one of which scientists know for certain is a sleep regulator.

In humans,people who get fewer than six hours of sleep per night are more likely to be obese.Moreover,starvation in humans,fruit flies,and worms has been shown to affect sleep,indicating that it is regulated,at least in part,by nutrient availability.However,the way in which sleeping and eating work in tandem(协同地)has remained unclear.

The researchers genetically changed C．elegans to“turn off'a nerve cell that controls sleep.These worms could still eat,breathe,and reproduce,but they lost their ability to sleep.With this nerve cell turned off,the researchers saw a severe drop in ATP levels,which is the body's energy currency.“That suggests that sleep is an attempt to conserve energy;it's not actually causing the loss of energy,'Raizen explained.

The researchers knocked out the KIN-29 gene to create sleepless worms,and the mutant(突变的)C．elegans accumulated much fat.They assumed that the KIN-29 mutants did not sleep is because they were unable to release their fat.To test this guess,the researchers again controlled the KIN-29 mutant worms,this time expressing a chemical substance that freed their fat.With that operation,the worms were again able to sleep.