Poisoned by Oxygen
There was a good reason for the scientists’ interest in oxygen poisoning. The problem was how to facilitate the work of divers. A man can survive in an atmosphere of pure oxygen for about twenty-four hours. If he breathes oxygen for longer than that, pneumonia ensues and, strange as it may seem, death due to asphyxia, which is a shortage of oxygen in the most important organs and tissues. A man can endure a pressure of two to three atmospheres not longer than one and a half to two hours. Then he becomes intoxicated with oxygen, loses coordination of movement, and suffers from mental distraction and loss of memory. If the oxygen pressure exceeds three atmospheres, convulsions will soon follow causing death.
Oxygen proves even more poisonous for animals which live where there is a critical lack of oxygen. This is how ascarides living in human intestines are combated. Oxygen is fed into the intestines, causing no danger to the man himself, but surely killing the parasites.
An excess of oxygen is not only detrimental to animals, but also to plants. It is interesting that, although plants saturate the atmosphere of our planet with oxygen, the Earth’s atmosphere is not good for them. They are rather short of carbon dioxide and, strange as it may seem, there is too much oxygen for them. According to recent investigations not only the usual concentration of oxygen but even as little as two per cent, that is one-tenth of what is to be found in the atmosphere, considerably retards photosynthesis. This means that plants have created an atmosphere quite unsuitable for themselves. Had there been less oxygen they would have grown and developed more rapidly.
Filed under oxygen | Tags: breathing, carbon dioxide, excess of oxygen, lack of oxygen, oxygen, oxygen poisoning, oxygen shortage | Comment (0)Oxygen, Energy and Wastefulness
The question arises why living organisms use atmospheric oxygen if energy can be obtained by mere fermentation. There are many important reasons for this. Fermentation never results in the complete oxidation of a substance and, therefore, little energy is released. If one gram-molecule of glucose is completely oxidized to carbon dioxide and water, 673 large calories will be obtained. But with fermentation, which results in the formation of ethyl alcohol and carbon dioxide, only as little as 25 large calories will be released, i. e. almost 27 times less. This means that anaerobes have to use 27 times as much glucose as aerobes to obtain the same amount of energy. The difference is, of course, appreciable and nature cannot tolerate such wastefulness.
Another important reason is that substances such as ethyl and butyl alcohol, lactic and butyric acid, acetone, etc., which are bad for the organism, are formed as a result of fermentation. It is not easy to dispose of these harmful substances.
Respiration frequently produces combustible gases. Microorganisms often release hydrogen. This is how microbes living in the intestine of termites breathe. Of the multicellular creatures, the larvae of some flies, in particular, release a great deal of hydrogen. Some organisms liberate not only hydrogen, but also methane and other gases, some of which are still not known, including spontaneously inflammable gases. It is a particularly beautiful sight when the gases, which have collected in the silt at the bottom of a pool, rise to the surface of the water and burn with a mysterious bluish flame.
How then have animals managed to change their way of breathing to such an extent and adapt themselves to an absence of oxygen? This did not prove difficult. At the dawn of life on the Earth there was little free oxygen and the earliest living creatures had to become anaerobes. It was not until the atmosphere became rich in oxygen that animals learned to burn energy-forming products completely. At the same time, the anaerobic method of breathing did not disappear but was passed on and finally came down to us.
As has been mentioned at the beginning, in all animals without exception the first stages of energy release proceed without oxygen. When aerobic animals felt like returning to the places where no oxygen could be obtained, they again had to restrict themselves to partial utilization of the energy contained in nutrient substances. To do this they had to remember how to render partially oxidized products harmless.
Filed under oxygen | Tags: aerobes, anaerobes, breathing, carbon dioxide, hydrogen, oxidation, oxygen | Comment (1)Methods of Oxidation
Oxidation by abstraction of hydrogen is termed fermentation; it results in the splitting of organic substances to form oxidized and reduced products and the liberation of the energy required by the organism.
The best known form of fermentation found in unicellular organisms is the breakdown of a glucose molecule into two molecules of ethyl alcohol (the reduced substance) and two molecules of carbon dioxide (the oxidized substance).
In multicellular organisms, the most common form of fermentation is lactic fermentation which involves the decomposition of carbohydrates, as, for instance, when a sugar molecule breaks down into two molecules of lactic acid which have less energy than the initial substance. The breakdown of carbohydrates is a gradual process consisting of a series of reactions. As a result, the oxygen in the molecule of sugar near to the inner carbon atom is transferred to the external carbon atom. Energy is thereby liberated.
There is also another method of oxidation, that of electron loss, but whether it can be used by living organisms has not been adequately studied.
Filed under oxygen | Tags: carbohydrates, carbon dioxide, hydrogen, multicellular organisms, oxidation, oxygen | Comment (0)Striving For a Breath
Tiny oxygen bubbles can often be observed on plants. The macroplea, beetles pick up these bubbles with their tiny legs and carry them to their antennae. After some time, the bubble disappears which makes us think that the beetles breathe with their antennae. If there are no gas bubbles of oxygen, the beetles cut the plant and wait for air to escape from its air channels. The same method is used by water weevils.
The larvae of macroplea and donicia beetles make incisions in plants and attach their spiracles to them. Other insects stick their stylets into the plants and suck oxygen out from the intercellular space. These oxygen-rich intercellular spaces are places favoured for pupation.
However, the caterpillars of the Brazilian paraponyx are even more ingenious. They build themselves a house from bits of green plants and, when these wither away, replace them. Consequently, during the hours of daylight, there is always plenty of oxygen in their nests, but at night, so as not to be choked by the carbon dioxide liberated by the plants, the caterpillars have to climb outside.
The amount of oxygen found in the stomachs and intestine of vertebrates is negligible. But certain living organisms which could find no place under the sun learned how to obtain oxygen. Not the least among them is the bot (the larva of the botfly) which lives in the alimentary tract of horses. Like all other insects, the bot has a tracheal system for respiration which is stronger and more ramified than that of larva living in the open. It also has red organs which are a conjugate formation consisting of many large red cells. A tracheal stem enters each cell and then branches out into numerous tracheoles in its protoplasm.
Filed under oxygen | Tags: breathing, carbon dioxide, intercellular, oxygen, plants | Comment (0)Shortage of Oxygen
Our atmosphere contains a great deal of oxygen and its loss is constantly made good by green plants. It seemed that man would never have to face a shortage of oxygen. However, it must be acknowledged with great distress that this hope is fading.
A few years ago the Japanese were forced to make reserves of oxygen available in ordinary, everyday conditions. The streets of Tokyo and other large cities in Japan are always packed with cars whose fumes poison the air with carbon dioxide and carbon monoxide. Such air is unsuitable for breathing, although it still contains sufficient oxygen.
The traffic wardens who are working for many hours in the streets are unable to last out a whole shift. To avoid excessive poisoning, they have to be supplied with oxygen. It is now a long-standing practice to provide police stations with cylinders of compressed air so that the policemen can take a breath of good air from time to time. Now they have started to install oxygen machines in the streets of Tokyo for passers-by, too, similar to the aerated water machines that are to be found in many cities the world over. This means that everybody can put a coin in the machine and refresh his lungs with oxygen.
Filed under oxygen | Tags: atmosphere, breathing, carbon dioxide, lungs, oxygen | Comments (2)