We found that animals in breathing give carbon dioxide to the air. Also that it is added to the air in the burning of a candle. In the same way it is given off in the burning of coal, wood, oil, etc. As a result what do you think should happen to the amount of carbon dioxide in the air? But an examination of the air year after year indicates that there is no increase in the amount of this gas. What do you conclude from this?

Another interesting fact gained from the examination of the air is that the oxygen of the air does not decrease in quantity. In the solution of our problem, therefore, a number of smaller problems must be solved. The first of these will be indicated by a fact that is familiar to you. W r hat is the appearance of partially burned plant material? What does this indicate? Since plants can grow in soil which con tains no carbon, what will you suspect is the source of the carbon ?

Proof that Carbon Compounds are Made in Leaves of Plants

One of the most common plant sub stances containing carbon is starch. There is no starch in the soil or in the air, therefore it evidently must be made within the plant.

Plant Starch Science Project Experiment

To prove that starch is manufactured in a leaf place a geranium in a dark closet for twenty-four hours, then remove a leaf and test for starch. This is done by first removing the green coloring matter, by soaking the leaf in alcohol, and then adding iodine, which gives a blue color if starch is present. What is the result? After this leaf has been removed, set the entire plant in the sunlight, first placing upon several leaves pieces of black cloth or thin strips of cork which completely exclude the light from the portions of the leaves covered. After a few hours, remove and test several leaves for the presence of starch. What is the result? What two things are proved by this experiment?

What Raw Materials are Used by Leaves in Making Starch?

Analysis shows that starch is made of the following fundamental substances or elements: Carbon, 6 parts; hydrogen, 10 parts; oxygen, 5 parts. This is conveniently written, C6H10O5.

Water, which is made of two parts of hydrogen and one part of oxygen (H2O), and carbon dioxide, composed of one part of carbon and two parts of oxygen (CO2 ), both of which are accessible to the leaf, contain the elements necessary for the formation of starch. If they were combined, the result might be represented as follows: Carbon dioxide (CO2 )+ Water (H2O) = Starch (C6H10O5). It will be noted that to get sufficient carbon for the starch, it is necessary that six parts of carbon dioxide enter into the combination; and to provide the proper proportion of hydrogen, five parts of water must combine with the carbon dioxide. The action may then be represented as follows: Six parts of carbon dioxide might combine with five parts of water to form one part of starch or

6CO2 +5H2O=C6H10O5

But if six parts of CO2 unite with five parts of H2O to form starch (C6H10O5), it will be noticed there is an excess of oxygen, so that the action will finally be represented as follows:

6CO2 +5H2O = C6H10O5 +6O2

If in the leaf, therefore, carbon dioxide and water actually do unite in forming starch, oxygen should be given off. Does this occur?

Do Plants Give off Oxygen in Making Starch?

Plant Oxygen Science Project Experiment

Place some aquarium plants under a funnel in a jar of water. Over the neck of the funnel put an inverted test tube filled with water. Place the jar in the sunlight. What do you observe?

Remove the test tube without allowing any of the contained gas to escape, and pass into the mouth of the test tube a glowing ember. What happens? What does this prove?

The work that the green leaf does with the assistance of sunlight in combining carbon dioxide and water into starch is called photosynthesis (from two Greek words: photo, light, and synthesis, putting together)

Proof That Plants use Carbon Dioxide in Making Starch

The fact that oxygen is given off by plants is an indication that carbon dioxide and water are used by the plant in making starch. It can easily be proved by the following experiment that carbon dioxide is used by plants during the process of starch-making.

Plant Carbon Dioxide Science Project Experiment

Pass into a jar sufficient carbon dioxide to replace the air almost entirely. Put into the jar a green plant which has been kept in the dark for twenty-four hours. Pass a lighted taper into the jar. What is the result? Also pass into the jar a glass rod from which is hanging a drop of limewater. What is the result? Cover the jar tightly and place it where it will be exposed to sunlight. After several days again test the contained air with the limewater and the lighted taper. Results? Conclusions?

Amount of Carbon Dioxide Removed From the Air in Making Starch and Wood

The woody sub stance of plants (cellulose) is also made of carbon, hydrogen, and oxygen in the same proportion as in starch. Wood, therefore, represents a certain amount of carbon dioxide taken out of the air and combined with water. It has been calculated that for every pound of starch or cellulose (wood manufactured by a plant) 1.6 pounds of carbon dioxide are needed. From an acre of ground several tons of dry hay may be obtained. A large proportion of the dry hay is cellulose, or material of a similar composition. Considering this fact, calculate approximately how much carbon dioxide will have been taken from the air by a ten-acre field of hay during one season.

The coal which we burn has had a similar origin. It was formed from many generations of plants which formed layer after layer of vegetable matter. This was partially oxidized and then was covered by sediment which finally became formed into rock. Soft or bituminous coal clearly shows the layers of vegetable matter of which it is composed.

Soft or bituminous coal occurs in great beds usually more or less horizontal. Anthracite or hard coal is found in portions of the country where the strata or layers of the rock have been very much crumpled. This crumpling process has evidently been accompanied by a high temperature which has driven from the accumulated vegetable matter many compounds, leaving almost pure carbon.

Just as we have found that the starch is made by plants, only under the action of the energy of sunlight, so likewise in the cases of wood and coal the energy of the sun has been necessary. What, therefore, may be considered to be the final source of the energy given out in the process of the burning of wood or coal? The amount of heat procured by burning a piece of coal may be considered to be a measure of the amount of the sun’s energy necessary to separate the carbon from the oxygen of carbon dioxide in the process of photosynthesis.

We are now able to understand why the relative quantities of oxygen and carbon dioxide in the air remain the same year after year.

What are the chief ways in which oxygen is removed from the air?
How is it restored to the air?
How do you suppose the composition of the air before the carboniferous period (the period when most coal was formed) differed from the composition of the air now?

Almost all plants are green. Is there any connection between the possession of this green coloring matter (chlorophyll) and the ability to make starch ?

Is the Green Coloring Matter (Chlorophyll) Necessary for Making Starch

Place a plant whose leaves have white streaks or spots (Tradescantia is a good plant to use) in the sunlight for several hours. Test the leaves for starch. Result? Conclusion? Experiments might, also be performed which show that it is only the living leaf that will manufacture starch.

How fish live in a balanced aquarium

Fish and other animals may be kept for long periods of time without being fed if they are in aquaria containing green plants. In such aquaria the green plants do not decrease in quantity. These aquaria are known as balanced aquaria.

(a) Breathing. From what you have already learned, ex plain how the fish get a supply of oxygen. What do you suppose becomes of the carbon dioxide produced ?

(b) Food Supply. In a balanced aquarium, what do the fish eat? A fish or any other living thing needs food not only to furnish fuel which may be oxidized to set energy free, but it must also have food to replace the waste which is occurring in the different parts of the body, and for growth if there is any growth going on.

Foods, therefore, may be divided into energy-producing food and tissue-forming foods. The tissue-forming portion of foods is made up of complex substances called proteins and certain mineral salts. The proteins, when oxidized, will produce energy, but the chief energy-producing portions of food are carbohydrates (starch and sugar) and fats.

Since fish of the balanced aquarium maintain their size and are active, what must be obtained from the plants?

Since the plants do not decrease in quantity, what must they be able to do?

We already have learned from what they make carbohydrates. Explain. Carbohydrates in turn are some times changed by the activity of the living matter into fat. For the manufacture of proteins, the plant must not only have carbon, hydrogen, and oxygen, which may be obtained from the carbon dioxide and water, but must also have nitrogen and other elements. The wastes of the fish contain all these needed elements.

In swimming about, the fish are continually exerting energy. What is the final source of this energy?

The relation of the plants and animals in the balanced aquarium is represented in the diagram. What do you think would happen to animals, including man, if there should be no more green plants? Explain.

Summarize in a sentence or two the importance to us of the carbon dioxide of the air.

Oxygen and Carbon Dioxide Science Project Reports

1. Rapidity of starch manufacture in a leaf.

2. Keeping a balanced aquarium.

3. The world’s food supply.