All other animals, and all plants as well, are surrounded by and use practically the same things from their environment as we do. The potted plant in the window, the goldfish in the aquarium, your pet dog at home, all use, as we will later prove, the factors of their environment in the same manner. Air, water, light, a certain amount of heat, soil to live in or on, and food form parts of the surroundings of every living thing.
An experiment that shows the air contains about four fifths nitrogen.
The Same Elements found in Plants and Animals as in their Environment.—It has been found by chemists that the plants and animals as well as their environment may be reduced to about eighty very simple substances known as chemical elements. For example, the air is made up largely of two elements, oxygen and nitrogen. Water, by means of an electric current, may be broken up into two elements, oxygen and hydrogen. The elements in water are combined to make a chemical compound. The oxygen and nitrogen of the air are not so united, but exist as separate gases. If we were to study the chemistry of the bodies of plants and animals and of their foods, we would find them to be made up of certain chemical elements combined in various complex compounds. These elements are principally carbon, hydrogen, oxygen, nitrogen, and perhaps a dozen others in very minute proportions. But the same elements present in the living things might also be found in the environment, for example, water, food, the air, and the soil. It is logical to believe that living things use the chemical elements in their surroundings and in some wonderful manner build up their own bodies from the materials found in their environment. How this is done we will learn in later chapters.
What Plants and Animals take from their Environment. Air.—It is a self-evident fact that animals need air. Even those living in the water use the air dissolved in the water. A fish placed in an air-tight jar will soon die. It will be proven later that plants also need air in order to live.
Apparatus for separating water by means of an electric current into the two elements, hydrogen and oxygen.
Chart to show the percentage of chemical elements in the human body.
Water.—We all know that water must form part of the environment of plants and animals. It is a matter of common knowledge that pets need water to drink; so do other animals. Every one knows we must water a potted plant if we expect it to grow. Water is of so much importance to man that from the time of the Caesars until now he has spent enormous sums of money to bring pure water to his cities. The United States government is spending millions of dollars at the present time to bring by irrigation the water needed to support life in the western desert lands.