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An essential scientific process 一个至关重要的科学过程
All life on the earth depends upon green plant .using sunlight , the plants produce their own food . Then animals feed upon the plants . They take in the nutrients the plants have made and stored . But that,s not all . Sunlight also helps a plant produnce oxyen . Some of the oxygen is used by the plant , but a plant usually produces more oxygen than it uses . The excess oxygen is necessary for animals and other organisms to live .
The process of changing light into food and oxygen is called photosynthesis . Besides light energy from the sun , plants also use water and carbon dioxide . The wate gets to the plant through lts roots . The carbon dioxide enters the leaves through tiny openings called stomata . This is where photosynthesis takes place . Chloroplasts contain the chlorophylls that give plants their green color . The chlorophylls are the molecuce that trap light energy . The trapped light energy changes water and carbon dioxide to produce oxygen and a simple sugar called glucose .
Carbon dioxide and oxygen move into and out of the stomata . Water vapor also moves out of the stomate . More than 90 percent of the water a plant takes in through its roots escapes through the stomata . During the daytime , the stomata of most plants are open . This allows carbon dioxide to enter the leaves for photosynthesis . As night falls , carbon dioxide is not needed . The stomata pf most plants close . Water loss stops .
If photosynthesis ceased , there would be little food or other organic matter on the earth . Most organisms would disappear . The earth,s atmosphere would no longer contaln oxygen . Photosynthesis is essential for life on our planet .
Real-World Robots 现实世界中的机器人
When you think of a robot , do you envision a shiny , metallic device having the same general shape as a human being , performing humanlike functions , and responding to your questions in a monotone voice accentuated by high-pitched tones and beeps? This is the way many of us imagine a robot , but in the real world , a robot is not humanoid at all . Instead a robot often is a voiceless , box-shaped machine that efficently carries out repetitive or dangerous functions usually performed by humans . Today,s robot is more than an automatic machine that performs one task again and again . A modern robot is programmed with varying degrees of artificial intelligence-that is , a robot contains a computer program that tells it how to perform tasks associated with human intellgence , such as reasoning , drawing conclusions , ang learning from past experience.
A robot does not possess a human shape for the simple reason that a two-legged robot has great difficulty remaining balanced . A robot does , however , move from place to place on wheels and axles that roll and rotate . A robot even has limbs that swivel and move in combination with joints and motors . To find its way in its surroundings , a robot
utilizes various built-in sensors . Antennae attached to the robot,s base detect anything they bump into . If the robot stqrts to teeter as it moves on an incline , a gyroscoper or a pendulum inside it senses the vertical differential . To determine its distance from an object and how quickly it will reach the object , the robot bounces beams of laser light and ultrasonic sound waves off obstructions in its path . These and other sensors constantly feed information to the computer , which then analyzes the information and corrects or adjusts the robot,s actions . As science and technology advance , the robot too will progress in its functions and use of artificial-intelligence programs .
A record-breaking rover 破纪录的漫游车
NASA,S mars rover opportunity has boldly gone where no rover has gone before-at least in terms of distance . Since arriving on the red planet in 2004 , opportunity has traveled 25.01miles , more than any other wheeled vehicle has on another world .
On july 27 ,after years of moving about on martiong ground , the golf-cart-sized opportunityhad driven more than 24 miles , beating the previous record holder-a soviet rover sent to the moon in 1973.
“This is so remarkable considering opportunity was intended to drive about 1 kilometer and was never designed for
distance ,”says john callas , the mars exploration rover project manager . He works at nasa,s jet propulsion laboratory in pasadena , california . “but what is really important is not how many miles the rover has racked up , but how much explortion and discovery we have accomplished over that distance .”
OPPORTUNITY
The solar-powered opportunityand its twin rover , spirit , langed on mars 10years ago on a mission pit . But opportunity has continued to collect and analyze martian soil and rocks .
During its mission , opportunity has captured , and sent back to earth , some 187 ,000 panoramic and microscopic images of mars with its cameras . It has also provided scientists with data on the planet,s atmosphere , soil , rocks , and terrain . MARA THON ROVER
The rover doesn,t seem to be ready to stop just yet . If opportunity can continue on , it will reach another major investigation site when its odometer hits 26.2 miles . Scientists call this site marathon valley , because when the rover reaches the area , it will have traveled the same distance as the length of a marathon since its arrival on mars . Researchers believe that clay minerals exposed near marathon valley could hold clues to mars,s ancient environmen . Opportunity,s continuing travels will also heip researchers as they plan for an eventual human mission to the red planet .
Lightening Strikes
Three years ago a bolt of lightning all but destroyed lyn miller,s house in aberdeen-with her two children inside . “there was a huge rainstorm ,”she says , recalling the terrifying experience . “my brother and i were outside desperately working to stop floodwater from coming in the house . Suddenly i was thrown to the ground by an enormous bang . When i picked myseif up , the roof and the entire upper storey of the house had been demolished . The door was blocked by rubble , but we forced our way in and found the children , thankfully unharmed . Later i was told to be struck by lightning is a chance in a million .” in fact , it,s calculated at one chace in 600,000. Even so , dr mark keys of AER Technology ,an organisation that monitors the effects of liahtning , thinks you should be sensible , “i wouldn ,t go out in a storm -but then i,m quite a careful person .” he advises anyone who is unlucky enough to be caught in a storm to get down on the ground and curl up into a ball , making yourself yourself as small as possible .
Lightning is one of nature ,s most awesome displays of sheer power . No wonder the ancient greeks thought it was zeus , father of the gods , throwing thunderbolts around in anger 250 years ago , benjamin franklin , the american scientist and statesman , proved-that lightning is a form of electricity , but scientists still lack a complete understanding of how it works. Occasionally there are warning signs . Positive electrical charges streaming upwards from trees or church spires may glow and make a buzzing noise ,and people,s hair can stand on end . And if you fear lightning , you ,ll be glad to know that a company in america has manufactured a hand-help lightning detector which can detect it up yo 70 kms away , sound a warning tone and monitor the storm,s approach.
Nancy wilder was pluying golf at a club in surrey when she was hit by a bolt of lightning . Mrs wilder,s heart stopped beating , but she was resuscitated and , after a few days in hospital , where she was treated for burns to her head , hands and feet ,she was pronounced fit again . Since that time , she has been a strictly fair weather golfer . In fact , a golf course is one of the most dangerous places to be during to be during a thunderstorm . The best place to be is inside a car!
The largest number of people to be struck by lightning at one time was in september 1995 when 17 players on a football pitch were hit simultaneously . The most extraordinary aspect of the strike was the fact that 11 of the victims-seven adults and four children-had butn patterns of tiny holes at 3 centimetre intervals on each toe and around the soles of their feet. Harold deal , a retired electrician from south carolina , USA, was struck by lightning 26 years ago . He was apparently unhurt , but it later emerged that the strike had damaged the part of the brain which controls the sensation of temperature . Since then the freezing south carolina winters haven,t bothered harold , since he is completely unable to feel the cold . Animals are victims of lightning too . Hundreds of cows and sheep are killed every year , largely because they go under trees . In east anglia in 1918,504sheep were killed instantaneously by the same bolt of lightning that hit the ground and travelled through the entire flock . Lightning is also responsible for starting more than 10,000 forest fires each year world-wide .。