About fifty years ago, plant physiologists set out to grow roots, by themselves in solutions in laboratory flasks. The scientists found that the nutrition of isolated roots was quite simple. They required sugar and usual minerals and vitamins. However, they did not require organic nitrogen compounds. These roots got along fine on mineral inorganic nitrogen. Roots are capable of making their own proteins and other organic compounds. These activities by roots require the energy of course. The process of respiration uses sugar to make the high-energy compound ATP, which drives the biochemical reactions. Respiration also requires oxygen. Highly active roots require a good deal of oxygen.
Ageing is a normal process of human development that takes place on several levels: biological, psychological and social although it is not certain what causes ageing, most gerontologists would agree that ageing is the result of a combination of both internal and external processes. The "wear-and-tear theory" compares the human body to a machine that over time wears down from use. According to this theory, bodily systems receive cumulative damage from both external forces, such as toxins, released as a result of metabolism. Cells become damaged and increasingly fail to reproduce or repair themselves. They die off in larger numbers as we age. the "combination theory" explains that influences such as stress and diet, each person is born with a genetically predetermined life expectancy that cannot be exceeded This interaction of external factors and internal programming would account for individual variations in the life span. The mystery surrounding why we age is still a topic of numerous ongoing studies. Perhaps, one day we will truly know why we age.
Read the passage:
The second half of the twentieth century saw more changes than the previous two hundred years. There were many remarkable advances in medicine that helped to increase our average life expectancy way beyond that of our ancestor's Incredible innovations such as television changed the way we spend our leisure hours. Perhaps the most important breakthrough, however, has been the microchip. Nobody could have imagined, when it was first invented, that within a matter of years, this tiny piece of silicon would be found in almost every household object form the kettle to the video recorder, And nobody could have predicted the sudden proliferation of computers that would completely change our lives, allowing us to access information from the other side of the world via the internet /www or send messages around the world by e-mail at the touch of a button. Meanwhile, research into other aspects of information technology is making it easier and cheaper for us to talk to friends and relations around the world.
Extraterrestrial life has so far been the stuff of science fiction, Yet NASA, the American space agency, is taking the idea so seriously that it is pondering how to dispose of its Galileo spacecraft, at present orbiting Jupiter, without harming possible alien lifeforms on one of Jupiter moons, Europa > NASA is worried that Galileo might blunder into Europa, contaminating it with earthly organisms. The best way to stop this happening the agency believes is to crash Galileo deliberately into Jupiter.
Promotion
