Breathing—The Bird and the Insect Ways
YOU do it about 23,040 times each day and yet you are hardly aware of it. What is it? Breathing. Your respiratory system is so well designed and operates so efficiently that you hardly notice that you are taking a breath at this very moment.
Of course, if you were on top of a mountain, where the air is very thin, it wouldn’t be so easy to breathe, would it? Or if you were swimming under water for any length of time you would soon become very much aware of the need to take a breath. Yet birds can fly at high altitudes and have no difficulty in breathing. And there are some insects that, although dependent upon the atmosphere for oxygen, can breathe under water. How do they do it? A close look at how birds and insects breathe reveals truly remarkable intelligence and design.
Bird Breathing
Anyone who has ever flown in an airplane is aware of two important factors necessary for flight—a light frame and plenty of fuel. The design of the bird’s respiratory system takes care of both needs.
High-energy activity burns up oxygen very quickly. A human makes up his oxygen deficiency by breathing deeper and faster. At high altitudes man has to slow down and rest frequently to give his system time to make up his blood oxygen level. Just imagine if a bird suffered the same effects while flying! But the respiratory system of the bird saves him this embarrassment so that even if you encounter him at 20,000 feet (6,100 m), he shows no sign of difficulty. His eyes do not bulge, his face is not pale and he is not even puffing. How does he do it?
Well, his breathing apparatus is designed to absorb oxygen so much more efficiently. Human lungs are bags or bellows that fill and empty. Not so with birds’ lungs. They are unique. Air goes into the lung, as normal, through the front end. But then the air passes right on through the lung and out into various thin-walled air sacs, which are located in the chest and abdominal cavity. (See illustration.) Back in 1758 a man named John Hunter discovered something truly surprising. He found that a bird with a blocked windpipe and a broken wing bone could still breathe. How was this possible?
The bones of birds do not contain marrow; they are hollow, containing air. The hollow air spaces in the bones are connected to the air sacs, which, in turn, are connected to the lungs. So when the bird’s windpipe was closed, the air passed to and from the lungs by means of the broken, hollow wing bone. What a cunning way to take care of weight and fuel problems at the same time—fuel tanks distributed through the framing! But what about fuel storage?
Actual storage of fuel is minimal. The bird picks up fuel, or oxygen, en route—in midair! The air passing through all those sacs and passages comes in contact with a large area of tissue, allowing for greater absorption of oxygen before exhalation. However, flying at high altitudes is an energy-intensive business. Fuel ought to be used as efficiently as possible. So, built into the bird’s respiration equipment is a system known as countercurrent flow. It enables the bird to extract oxygen from the air quickly and efficiently by means of a very simple principle.
In the bird’s lung, air and blood approach each other from opposite directions. As the air flows through the lung, it gives up more and more oxygen to the blood, and the blood can continuously take up more and more oxygen. In other words, the “thirsty” venous blood first reaches air that is already deficient in oxygen and that has, as it were, only a few “droplets” of oxygen left in it. The “thirsty” blood soaks it up and passes on to the “wetter” air, in which there is more oxygen. By now the blood is not so “thirsty,” so it soaks up less and less oxygen. The end result of this remarkable process is the extremely efficient extraction of oxygen from the air. And that is precisely what the bird needs in order to fly at high altitudes!
Insect Breathing
Have you ever considered the possibility of an ant the size of an elephant? Imagine the power it would have! An ant can carry twice its own weight. And small though insects are (the biggest, the Atlas moth, is only 10 to 12 inches [25 to 30 cm] from wingtip to wingtip) they have enormous appetites. Why, in North Dakota grasshoppers caused $1,714,000 (U.S.) worth of crop and rangeland damage in just one year! What would the damage have been if grasshoppers were the size of horses?
Well, there is no cause for alarm. The insect’s respiratory system keeps him in his place—sizewise. According to Scientific American, the insect’s respiratory system, which the magazine called “a refinement of biological engineering almost past belief,” has a built-in size-limiting factor! Furthermore, just as the bird’s respiratory system is ideal for flying, the insect’s is ideal for his way of life. How so?
Insects are energy factories. For their size, they carry out truly Herculean tasks. So their demand for oxygen is very high. However, insects do not have lungs. Nevertheless, it is indeed doubtful that you will ever come across a breathless insect! Why? Because they have a respiratory system that is designed to cope with an unlimited demand.
During the embryonic stage, the skin of an insect pushes inward at many points to form hollow tubes, which open out to the atmosphere. As these tubes grow deeper and deeper into the insect’s body, they branch many times, each branch becoming narrower and narrower. Finally, one or more of these tubes come in contact with each cell. Thus, each cell has a direct pipeline to the atmosphere, which means that oxygen is immediately available for use without its having to travel through a blood circulation system. And that is just what the insect needs to carry on his high-energy activity!
But the problem with a system of tubes to breathe through is that you need a two-way flow—oxygen going in and carbon dioxide going out. The tubes in the insect can bring oxygen in, but what happens to the carbon dioxide? Well, unlike oxygen, carbon dioxide diffuses more easily through tissue. So it doesn’t try to get out back through the tubes. Rather, it passes out of the insect through its skin.
Although they are dependent upon the atmosphere for their supply of oxygen, some insect larvae live under water. How do they breathe there? Some send up a “snorkel” tube—at times equipped with a valve in case the water gets rough and threatens to get into the tube. Others live in a “diving bell,” that is, a bubble of air. Of course, as they use up oxygen in the bubble, it must be replaced. Researchers were long puzzled by the fact that the insect could stay under water long after it should have used up the supply of oxygen in the bubble. How was this possible?
The process of diffusion comes into play. As the oxygen pressure in the bubble drops below the oxygen pressure in the surrounding water, the oxygen in the water rushes into the bubble. (Remember, water is made up of two atoms of hydrogen and one of oxygen.) ‘But why doesn’t the bubble collapse?’ you may be wondering. Well, there is nitrogen in the air of the bubble, and it does not diffuse into water; it prefers to stay in the bubble. So while the insect larva may not need nitrogen for his metabolism, his “life-support system” certainly is dependent upon it!
Surely, after taking a look at how birds and insects breathe, you agree that the respiratory systems of these creatures reflect truly remarkable intelligence and design. But do you find it easy to believe that blind chance or the birds and the insects themselves developed these systems of respiration, which are so dependent on scientific principles? Or do you draw the same conclusion as did the famous inventor Thomas Edison, who said: “After years of watching the processes of nature, I cannot doubt the existence of a Supreme Intelligence”?
[Picture on page 22]
A Bird’s Respiratory System
Trachea
2 Lungs
Sacs
[Picture on page 23]
An Insect’s Respiratory System—How It Works
No Lungs
Tube
Cells