Extreme conditions produce extremely tough plants. The big difference between "drought—tolerant" plants and these tough plants: metabolism. Many different kinds of plants have developed tactics to weather dry spells. Some plants     1     of water to see them through a drought; others send roots deep down to subsurface water supplies. But once these plants use up their stored water or tap out the underground supply, they cease growing and start to die. They may be able to handle a drought of some length, and many people use the term "drought tolerant" to describe such plants, but they never actually stop needing to     2     water, so Farrant prefers to call them drought     3    .

Resurrection plants, defined as those capable of recovering from holding less than 0.1 grams of water per gram of dry mass, are different. They lack water—storing structures, and their existence on rock faces prevents them from     4     groundwater, so they instead developed the ability to change their metabolism. When they detect a/an       5     dry period, they change their metabolisms, producing sugars and certain stress—     6     proteins and other materials in their tissues. As the plant dries, these resources take on first the     7     of honey, then rubber, and finally enter a glass—like state that is "the most stable state that the plant can maintain," Farrant says. That     8     the plant's metabolism and protects its dried—out tissues. The plants also change shape, shrinking to minimize the surface area through which their remaining water might evaporate. They can recover from months and years without water, depending on the species.

What else can do this dry—out—and—revive trick? Seeds—almost all of them. At the start of her career, Farrant studied seeds such as avocados(牛油果) , coffee and lychee(荔枝). Though     9    , such seeds are delicate — they cannot bud and grow if they dry out. Most seeds can wait out the dry, unwelcoming seasons until conditions are right and they sprout. Yet once they start growing, such plants seem not to retain the ability to hit the     10     button on metabolism in their stems or leaves.

【推荐2】Directions: Fill in each blank with a proper word chosen from the box. Each word can only be used once. Note that there is one word more than you need.

No child or young athlete should be subjected to genetic testing to find sporting talent or improve performance, conclude the experts in a statement published in the British Journal of Sports Medicine.

The scientific evidence on the effectiveness of these     1     tests is simply far too weak to back their use, says the experts in the fields of genomics, exercise, sports performance, etc. While the science of genomics has advanced rapidly over the past decade, the ability to interpret the meaning of genetic test results is still at a relatively early stage.

But that has not stopped the growth of the “direct to consumer” genetic tests, which claim to be able to spot children’s athletic talents or tailor training to     2     performance. This fast - growing market has caused fears that the still limited level of knowledge on the genetics of sports performance is being     3     for commercial gain.

To inform the statement, the panel looked at the availability of DIY genetic tests. It found 39 companies     4     tests associated with sport or exercise performance or injury - almost twice as many as in 2018.

The claims included: “    5     your training based on your sports genetics,” “Give parents and coaches early information on their child’s genetic     6     for success for sports,” and “We use your DNA results to help you lose fat, build muscle, get fitter.”

But the     7     of any good scientific data to guide selection of which variants to test weakens the value of multiple testing. Besides, while there is some evidence to suggest a link with enhanced physical performance, it is very weak, making the     8     value of these tests “actually zero,” says the statement.

The statement emphasizes the     9     of change in gene sequencing technology has got much faster than regulation. And it points out the importance of counselling before any genetic test is taken.

“While further evidence will undoubtedly emerge around the genetics of sport performance in the future, the data are currently very     10    . Therefore, in this stage of limited knowledge, no child or young athlete should be exposed to genetic testing to define or alter training or for talent identification aimed at selecting gifted children or adolescents,” it concludes.