Plant and animal cells respire sugar. That is, within the cell, sugar is broken down in a series of steps, and the energy holding the various atoms of the sugar molecule together is transferred away for use within the cell.
This breakdown, called respiration, goes on until each sugar molecule has been broken down into carbon dioxide and water.
Respiration furnishes the energy for other cell activities such as reproduction, protein and fat making, and, in some animals, temperature regulation.
Plants Can Make Sugar
Using energy absorbed from the sun, plant cells begin with water taken from the soil and carbon dioxide removed from the air, making sugar from them. This is a sort of the reverse of respiration, although the chemical route is different.
Because this process uses light, it is called photosynthesis. (Photo means light.) Photosynthesis is the manufacture of sugar within plant cells using light energy.
Photosynthesis Process
The process of photosynthesis is extremely complicated. The many intermediate steps between carbon dioxide and the finished sugar molecule are not well understood, but several things that are known about the process are of interest to gardeners.
Only Green Plants Can Photosynthesize
The green pigment chlorophyll is closely involved in absorbing light energy from the sun and changing it to chemical energy.
Chlorophyll, made up of small, usually, disc-shaped bodies called chloroplasts, absorbs solar energy. In contrast, the chloroplasts furnish a site for the chain of reactions ending with water and carbon dioxide being combined to form sugar. This reaction produces oxygen as a side product.
The process summarized in this equation occurs today only in green, living plants growing suitably in a favorable environment.
With all his moon rockets, satellites, and other fancy gadgets, man cannot duplicate this process, although millions of dollars are spent each year in the attempt.
Why Is Photosynthesis So Important?
Think of all the living creatures on earth, from microscopic germs through the little animals and wildflowers of our woods to the great beasts and trees of tropical forests, to mankind himself. What keeps them all going?
Either they cat each other, or they cat plants. Take a man, for example; he eats meat, eggs, cheese, and so on, along with his vegetables and salads, but the animals furnishing the meat and eggs eat grain, hay, or grass.
Therefore we can conclude that the animal kingdom is dependent on the plant kingdom for food, that is, for a source of energy.
In both plant and animal kingdoms, food is used to sustain daily life, provide for growth and blooming, and supply the energy for reproduction. And now, the final point: all of this energy is solar energy transformed by photosynthesis.
We know our plants grow and that if we fertilize them, they may grow better, but is the fertilizer to have full credit for plant growth? No, although it is very necessary for the plant’s efforts literally to build itself.
Nitrogen and Carbohydrates
Nitrogen is needed to make protein, which, in turn, is the main ingredient of protoplasm, the living stuff of all organisms. But the main building block in making a protein is a carbohydrate unit derived from photosynthetically-made sugar.
Likewise, fats and compound carbohydrates such as starch are built up from sugar units.
Phosphorus
Phosphorus is found in almost all fertilizers; we occasionally add more to our soil as superphosphate. So here is a direct tic with the photosynthetic process and respiration, too.
Light energy must be moved from one place to another when it is fixed in a chemical form. This is done through high-energy phosphate, thus making phosphorus essential to the plant.
Potassium
Potassium, too, enters the picture, along with many minerals needed in small amounts. The interior of a plant is a factory operating along lines more complex than anything man has ever dreamed of.
Observant Gardener
An observant gardener watches leaves turn so the flat surface faces the sun, gaining more light-gathering surface.
He may also realize that the shape of a tree is greatly determined by the need to keep one part of the tree from shading another part. Whoever saw ivy leaves turn inward toward the building on which the vine clings?
Does not a house plant “lean” toward the light? All of these phenomena are based on the need for light. Plants use light energy to make sugar, and they go about it wonderfully.
44659 by Dr. John P. Baumgardt