It’s a sound you will probably never hear, a sickened tree sending out a distress signal. But a group of scientists has heard the cries, and they think some insects also hear the trees and are drawn to them like vulture to a dying animal. Researchers with the US Department of
Agriculture’s Forest Service fastened sensors to the bark of drought-stricken trees clearly heard distress calls. According to one of the scientists, most parched trees transmit their plight in the 50-hertz to 50-kilohertz range. (The unaided human ear can detect no more than 20 kilohertz). Red
oak, maple, white pine, and birch all make slightly different sounds in the form of vibrations at the surface of the wood.
The scientists think that the vibrations are created when the water columns inside tubes that run along the length of the tree break, a result of too little water following through them. These fractured columns send out distinctive vibration pattems. Because some insects communicate at ultrasonic frequencies, they may pick up the trees' vibration and attack the weakened trees. Researchers are now running tests with potted trees that have been deprived of water to see if the sound is what attracts the insects. “Water-stressed trees also smell differently from other trees, and they experience thermal changes, so insects could be responding to something other than sound”, one scientist said.
Question 158: All the following are mentioned as possible factors in drawing insects to weakened trees EXCEPT .
A. thermal changes B. sounds C. changes in color D. smells
Question 159: It can be inferred from the passage that research concerning the distress signals of trees .
A. has been unproductive up to now B. is no longer sponsored by the government
C. was conducted many years ago D. is continuing
Question 160: Which of the following could be considered a cause of the distress signals of trees?
A. attacks by insects B. experiments by scientists
C. torn roots D. lack of water
Question 161: Which of the following is the main topic of the passage?
A. The effect of insects on trees. B. The vibrations produced by insects.
C. The mission of the U.S Forest Service. D. The sounds made by trees.
Question 162: The word “plight” in paragraph 1 is closest in meaning to _ .
A. condition B. cry C. need D. agony
Question 163: It can be inferred from the passage that the sounds produced by the trees
.
- are the same no matter what type of tree produces them
- cannot be heard by the unaided human ear
- fall into the 1-20 kilohertz
- serve as a form of communication among trees
Question 164: The word “parched” in paragraph 1 is closest in meaning to .
A. dehydrated B. recovered C. damaged D. burned
