1 . Have you ever stopped to consider how empty the world would look without trees? Below are five of the top benefits that trees provide.

    1     When adults who are feeling down spend time in the forest, they feel better. Forest therapy can range from simply walking among the trees for a couple of hours to meditating (冥想) in a forest. The adults note they become more confident and their mood improves after forest therapy.

Trees help you heal faster. Natural environments, including forests, help you reach a more positive state of mind.     2     In fact, sick people with exposure to nature heal faster than those who don’t, even if it’s just a view through a window!

Trees reduce air pollution and improve respiratory (呼吸的) health. Trees take in many harmful pollutants from our environment.     3    These forests reduce an estimated 670, 000 cases of respiratory illness and save 850 lives.

Trees provide oxygen. Trees are like the lungs of our Earth. They supply us with oxygen while taking away our carbon dioxide and ask for nothing in return. A single tree can provide enough oxygen for four people.     4    

Trees cool cities. Trees cool things down by offering shade and through evapotranspiration (蒸腾作用).     5     Trees even save your money on your electric bill. When a tree offers direct shade for your home, you’ll use less air conditioning.

A new study reveals that plants have their own “ bedtime alarm clock ” that helps them survive the night. Researchers at the University of York have discovered that plants possess an internal signal which they believe tells them     1     amount of sugar they have in their systems at dusk. Plants use sunlight to make     2     ( they ) own sugars from photosynthesis (光合作用）during the day and store them to provide energy during the night.

Plants’ ability to predict sunrise and estimate the     3     ( long ) of the night, as well as adjust metabolism (新陈代谢),     4     ( depend ) on a biological time-keeper called a circadian clock. This is a network of genes which drives rhythms of     5     ( rough ) 24 hours. Biologists think it is this signal, or so-called “ alarm ” ,     6     gives plants the information they need to adjust their metabolism in the dark nighttime hours to stay alive.

The researchers discovered a set of genes     7     ( regulate ) by the chemical compound superoxide, which     8     ( associate ) with metabolic activity. And they found by stopping the production of superoxide, they also stopped the effect of sugar     9     these circadian clock genes in the evening,     10     ( reveal ) the plants’ so-called “ alarm ” .