50.WHAT ARE BACTERIA?
Man’s relationship to bacteria is a very interesting one. We all know that many bacteria are harmful. Diseases such as typhoid fever, cholera, diphtheria, pneumonia, and all infections that occur in open wounds are each caused by a particular kind of bacteria. So man wages war on these bacteria.
Yet, without the action of other types of bacteria, life would be impossible on earth! In fact, man actually cultivates certain bacteria because he needs and uses them.
49.HOW IS THE SPEED OF WIND MEASURED?
On a windy day, it may seem to you that the wind is moving at tremendous speed. Then you hear the weather report and it says, “Winds of 10 to 15 miles per hour.” It’s easy for us to be fooled about the speed of the wind. But the exact wind speed is important to many people, so there are scientific ways of measuring the wind.
48.HOW DO PLANTS TAKE IN THEIR FOOD?
We must not forget that plants are living things. They eat, drink, and breathe, and without plenty of good food, they die. With the exception of two classes of plants, all plants manufacture their own food. Let’s see how they go about doing this.
The marvelous substance called chlorophyll in the cells of the leaves and often in the stem and flowers helps the living tissue of the plant to absorb the energy from sunlight. This energy transforms dead (inorganic) chemicals into life-giving (organic) chemicals. The name for this truly amazing process is photosynthesis.
