SCHOOL IN THE OPEN.

Star (Christchurch), Issue 18805, 6 July 1929, Page 20 (Supplement)

SCHOOL IN THE OPEN.

STUDIES IN THE GREAT OUT-OF-DOORS.

(By

J. J. S. Cornes,

8.A., B.Sc.)

The “Star” has arranged with Mr J. J. S. Comes, 8.A., B.Sc., to write a series of illustrated articles which will give teachers and others a fuller appreciation of the Great Out-of-Doors. They will deal with various aspects of plant and animal life, as well as with inanimate nature. Questions and material for identification will be welcomed.

BIOLOGY lI.—ENERGY OF LIVING THINGS. CCXCVII. New how is it that we, as examples of living creatures, are able to “do things.” Thanks to the inventive brains of men, we have at our disposal many inanimate “machines” which we can cause to “do things” for us. For example, a railway engine or motor can move us from place to place while we sit and do nothing. The engine is doing the work that otherwise would have to be done by our own, or a horse’s, muscles. Now the power of doing work of any kind is called “ energy.” So far as we know, there is a certain amount of energy in the universe : we can neither create more energy nor can we destroy any: all we can do is to change the form in which the energy manifests itself, and render it available to ourselves in the form most convenient for any given purpose. Energy of a Machine. To become possessed of energy an object must have had energy expended on it at some time. Thus, in the rail-way-engine the piston acquires from the steam’s expansion the energy necessary to turn the wheels; the steam has acquired its energy from the heatenergy liberated by burning coal—that is to say, chemical energy has been transformed into heat energy, and, to go back a step farther, the coal acquired its energy in consequence of the work done ages ago by the green plants whose fossilised remains are coal, for these plants secured and stored energy from the light and heat-energy of the Energy of a Living Object. Whence then do living creatures get the energy to carry on the “works' 1 which, together constitute life? From what source do you and I divine the energy that enables our bodies to do their work of living, no matter whether we are lazy or hard-working? Our bodies in many respects are the railway engines—they depend on fuel, and the combustion of fuel, for their i

energy. Part of this energy is manifested in the warmth of our bodies, part is used in enabling the organs (“working parts”) to do their work of moving the limbs, digesting our food, “noticing” what is going on around us, and so on. Our fuel is our food—but how and whence did our food acquire energy? Energy of Food. Now consider the nature of our food: some of it is animal, some vegetable—a little is mineral, e.g. ordinary salt, but as neither this nor water is “fuel ” we will here disregard them. But all the animal food that we take is either the actual flesh or the produce of animals that feed on plants or on smaller animals that do so. Sheep and cows are purely herbivorous; birds eat, in addition to seeds and leaves, insects, worms, and snails, small animals that feed on vegetable matter. Ultimately, then, we depend on green plants for our food supply, and therefore also for our supply of energy. We are thus led to inquire how and whence the green plants

obtained their energy, and how the starch and the oils, and the other substances which are to us the nutritious parts and products of green plants, come to have energy, and thus to be not only valuable, but absolutely necessary to us as “fuel” for-our life. Colour. I have intentionally used the epithet “green” several times because the answer to our inquiry lies in the green parts of plants. And here we must digress for a moment n order that you may understand what colour is, why some objects are white, others green or blue or any other colour. Of course, in the absence of all light there is no colour: in total darkness all things are black, because no light is either falling on, or being sent out from, their surfaces. But in light things appear coloured because part of the light that is falling on them is absorbed, and part is not absorbed, but is reflected from their surfaces, and on reaching our eyes produces the sensation of colour. White objects appear white because they reflect all the kinds of raj's of which sunlight is composed; but by employing a triangular prism of glass we can break up a beam of ordinary white light into all the colours of the rainbow, and make on a sheet of paper that we know to be white a band showing the seven colours, red, .orange, yellow, green, blue, indigo, violet, that together make the “spectrum” of white light; and all seven show up well because the paper does not absorb any, but reflects them all. Mark you, the bits of paper on which these colours respectively fall are the colours that they appear so long as the spectrum falls upon the paper. Now if a beam of ordinary white light is made to pass through an alcoholic solution of the substance which colours leaves green, chlorophyll (Greek chloros—green, and phullon—a leaf) and then to pass through a triangular glass prism, its spectrum thrown on a sheet of white paper shows a number of black bars across it. The darkest of these is in the red part of the spectrum, but there are broad, dusky bars too, in the violet and blue, and several narrower elsewhere. The dark bars are due to the absence of light, and they

therefore prove that the chlorophyll has stopped certain kinds of rays, especially red rays. Hence it is clear that chlorophyll absorbs and appropriates some of the light which falls upon it. Chlorophyll. Now light is one of the forms of energy, and anything that absorbs any of the light falling on it becomes thereby possessed of energy. Hence we see that chlorophyll is a contrivance for absorbing light-energy—literally, “a trap to catch a sunbeam”—and chlorophyll thus enables a plant to work, to do “upbuilding” work, as described in next article. But in order that you may realise how important is this “work” of plants, we will at once say that all life as we know it on this earth depends upon the work which chlorophyll enables plants to perform. If by some great catastrophe all chlorophyll were destroyed, there would follow in a short time the death by starvation of every living thing in the world. (To be continued next Saturday.)