724 MAN'S PHYSICAL WELFARE Coal, Oil, and Natural Gases Have Their Origin in Photosynthesis. Plant and animal materials have been transformed by geological processes involving high pressures and temperatures into such compounds as coal, oil, and natural gas. Methods have already been worked out for the direct conversion of carbohydrates such as cellulose to hydrocarbons similar to those found in petroleum. Photosynthesis may therefore be considered the "standby plant" to which we will have to resort when our petroleum and coal resources are used up. Man Has Not Yet Succeeded in Mastering Photosynthesis. So far nearly every likely idea concerning the chemical mechanism of photosynthesis has been proven to be wrong when tried out, but the intensive research now being carried out should yield some correct answers soon. STUDY QUESTIONS 1. Discuss photosynthesis as to (a) what it is, (b) why it is important, (c) what products have their origin in it, and (d) man's present knowledge of it. 2. Upon what does the rate of photosynthesis depend? 3. Is man able to carry out artificial photosynthesis today? 4. What is necessar>' to prevent famines today? 5. Work out a hypothesis to explain the following observations: An active leaf submerged in water and exposed to sunlight forms bubbles of gas on its surface, the number of bubbles being proportional to the intensity of the sunlight. 6. Differentiate between edible fats and oils, and mineral oils and waxes. 7. Why is photosynthesis spoken of as the most important chemical reaction in the world? 8. Explain how coal, oil, natural gas, and petroleum have their origin in photosynthesis. 9. Why can animals not use hydrocarbons for foods? 10. List the most important organic acids and give the origin of each. 11. Add as many oils as you can to those mentioned in this lesson, and give the uses of each. 12. Is it true that all living matter is dependent upon photosynthesis? Are mushrooms an exception?
UNIT X SECTION 2 FOODS ARE THE RAW MATERIALS OF LIVING ORGANISMS Introduction. No matter what type of cell is examined under the microscope (a drop of blood the size of a pin's head contains millions of cells), it will always be found to contain a slimy, viscous, semifluid material called "protoplasm," which is the living material itself. This protoplasm and the cell walls in which it is retained are colloidal materials. The processes by which cells, obtain foods, change it into new forms, discard waste products, and reproduce themselves are likewise colloidal in nature. For that reason the study of colloids was reserved for this Section, which is devoted to the study of foods. Matter in the Colloidal State Is the Vehicle of Life. In 1861 Thomas Graham found that certain substances in a solution would pass through a parchment paper while others would not. The former he called crystalloids and the latter colloids. It is only within the last twenty-five years, however, that the information has been obtained which shows that nearly every kind of matter may assume the colloidal state. The properties of colloids are more the result of the size of the particles than the nature of the particles dispersed. For that reason the colloidal state is considered to be a physical state of matter. Matter in the Colloidal State Exhibits Several Distinctive Properties. /. Brownian Movement. In 1827, long before Graham had coined the term "colloid," another Scotch scientist, Robert Brown, noticed peculiar movements of pollen grains in water as he examined them under the microscope. This constant zigzag motion, characteristic of all colloids, was later called the Brownian movement, in honor of the man who first observed it. 2. Tyndall Effect. This effect was named after the eminent Irish scientist, John Tyndall, who observed that the path of a beam of light 725