Paul could not sleep last night. He woke up early and sat up, and then lay down again. He felt terrible. "I must be sick," he thought, "but I must study for that test." He got up and looked for his history notebook. He finally found it under a pile of clothes on his chair. He went over his history notes, but he couldn’t remember any of the facts in his notes. "What shall I do" he thought.
Just then the telephone rang. He put down his notebook and picked up the telephone. "Good morning," Jack’s voice said. "You must be wrong about that test." "What do you mean" Paul asked weakly. "We’re not going to have a test today." Jack said, "I wrote down the date in my notebook. The test will be next Wednesday; it isn’t today. How do you feel this morning" "Fine," said Paul, "just fine!" Suddenly he really felt fine.
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 the 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 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.
The study of isolated roots has provided an understanding of the relationship between shoots and roots in intact plants. The leaves of the shoots provide the roots with sugar and vitamins, and the roots provide the shoots with water and minerals. In addition, roots can provide the shoo
A. A biochemical process.
B. The tip of a root.
C. A chemical compound.
D. A type of plant cell.
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