Food from the air

Everyone has seen plants growing, but have you ever thought     1     they get their food? In the seventeenth century, a European scientist     2     (call) Van Helmot asked this question. Like most people, he thought that plants must get their food from soil. However, Van Helmot decided       3     (test) the theory with experiments.

First, he dried some soil, put it into a pot and weighed it. Next, he weighed a small tree, planted it in the pot and added rain water. Then, he watered it     4     (regular) with rain water.

After five years, he removed the tree from the pot and weighed it again. He found that the tree had gained     5     huge amount of weight. When he weighed the soil, however, it was almost exactly the same as it had been five years    6    . So Van Helmot drew the    7    (conclude) that the tree grew by drinking water. Though it turned out to be wrong, he showed the importance of the use of scientific evidence to support ideas.

We now know that plants and trees make their own food. Their leaves, when exposed     8     the air and sun, are like factories    9     can change the energy from the sun into chemical energy. During this process (过程), oxygen and sugar     10     (produce). The oxygen is released back into the air, and the sugar is used by the plant as food.

In today’s Science class, we learnt that human beings have five senses. Our teacher, Mr. Smith, asked us to find out    1    plants have senses, too. After some research, I found that,     2    (like) human, plants have only one or two senses.

Some plants can see the light from the sun, and grow towards    3    . What is    4    (amaze) is that plants    5    like eating small insects can sense the soft touches of the insects on their leaves. After they sense the insects, they move their    6    (leaf) all of a sudden to catch them. It has also been discovered that some plants can feel whether the animals around them want to hurt them or not. No one really knows how the plants can do this. The results of a recent experiment    7    (carry) out by some Italian and German scientists are amazing.

It    8    (observe) that when some plants sense dangerous insects, they give    9    a kind of smell for protection—the smell can attract other insects in the distance which can kill the dangerous ones.

I never    10    (know) plants were so clever.