Which of the following biological theories of aging states that people age because their cells normal metabolism produces unstable oxygen molecules?
The wear-and-tear theory of aging asserts that the effects of aging are caused by progressive damage to cells and body systems over time. Essentially, human bodies "wear out" due to use. Once they wear out, they can no longer function correctly. Show
It is sometimes called simple deterioration theory or fundamental limitation theory. It's one of many theories on aging that continue to emerge. Some view aging as a more intentional process. This article explores the wear-and-tear theory of aging, its foundational scientific premises, and both the evidence for and against it. It also reviews different aging theories that compare with it. OJO_Images/Getty ImagesAn Overview of the Theories of AgingIt's important to recognize that there are several distinct theories of aging. The wear-and-tear theory is just one. Each theory has evidence for and against it. There are two primary categories of aging: programmed theories and error theories. Programmed theories of aging believe that aging is a normal process, just as puberty is a normal developmental process. These include:
Error theories of aging believe that aging is not something that is programmed to occur, but rather aging is due to a series of "accidents." These include:
Wear-and-tear theory of aging falls into this latter category of error theories. Programmed theories view aging as a natural process that follows a "healthy" cycle in the body. Error theories look at aging as an accident and "problem" to be solved. The differences go far beyond biology and become a philosophical discussion. Basic Tenets of Wear-and-Tear TheoryThe wear-and-tear theory basically states that bodies wear out after time. This theory can easily make sense when considering inanimate objects, from cars to clothes, that wear out and become less functional with time. Causes of Wear-and-Tear DamageA wide range of internal and external factors can damage body systems. Exposure to radiation, toxins, and ultraviolet light can damage genes. The effects of the body's own functioning can also cause damage. When the body metabolizes oxygen, free radicals are produced that can cause damage to cells and tissues. There are some cellular systems that don't replace themselves throughout life, such as the nerve cells of the brain. As these cells are lost, function eventually will be lost. Wear-and-tear theory sees cells as being like socks that only last so long before they become threadbare or get holes. They can patch themselves, like socks, but only so many times before they just don't work anymore. Within cells that continue to divide, the DNA can sustain damage and errors can accumulate. The simple act of dividing, again and again, shortens the telomeres of the chromosomes, eventually resulting in a senescent cell that can no longer divide. Oxidative damage in cells results in cross-linking of proteins, which prevents them from doing the jobs they are intended to do in the cells. Free radicals inside mitochondria, the powerhouses of the cells in your body, injure their cell membranes so they can't function as well. Evidence For and AgainstIt might simply seem that the wear-and-tear theory "makes sense" based on observations, but it's important to compare these gut feelings with what is scientifically known about the body and aging. Under the microscope, there are some processes that support wear-and-tear as a factor in aging, but several other findings call question to this process. There is evidence both for and against this theory. Evidence For
Evidence Against
Supporting EvidenceThe wear-and-tear theory of aging fits most closely with a perceived sense of aging. In fact, regardless of chronological age, the term "aging" is used to describe the progressive deterioration of a person or object. On a broad level, the wear-and-tear theory fits closely with one of the fundamental laws of chemistry and physics, that of entropy. This law states that all systems tend toward a state of increased entropy or progressive disorganization. Visually, there are structural changes with age in human skin and bones. On a cellular level, there are a number of functions which decline with age. Even with a good diet, cells have a decreased ability to absorb nutrients with age. Contrary EvidenceThe strongest evidence against the wear-and-tear theory is that bodies have a tremendous ability to repair the damage. DNA is equipped with DNA-repair genes (such as tumor suppressor genes) which work to repair genetic damage. In addition, some studies have found that the aging process may be partially or completely reversed by simply changing the microenvironment of cells or certain hormonal factors. Of course, not all damage can be repaired fully, and mistakes in repair may accumulate over time. Another argument against the wear-and-tear theory notes that organisms in their growth phase become stronger and stronger. Rather than starting out at the peak of performance, such as a car fresh off the assembly line or a new computer right out of the box, living organisms often start life fragile. They build strength and resilience with age. They are able to repair and replace most broken parts themselves. Finally, there are some circumstances in which wear-and-tear actually extends life expectancy. Yet another argument comes about when looking at the biochemical nature of the body. Why do lifespans vary so much between different species of animals? Why do some whales live almost twice as long as humans? Going against progressive deterioration and wear-and-tear: Why do salmon, after a long upstream energetic swim, spawn and then die, seemingly at the peak of physical condition? Bottom Line on What Causes AgingThe question of why aging occurs goes back much further than Weisman's theory proposed in the 1800s. Shakespeare addressed aging in his "seven ages of man," and religious texts have done so for millennia. While the wear-and-tear theory at first seems most natural, and makes the most sense based on observation, it becomes clear that there is much else going on in the body that cannot be explained by this theory. A more likely explanation, according to some researchers, is that the decrease of functioning that is seen as "tear" in the "wear-and-tear" theory is really the result, not the cause, of aging. Perhaps with an increased understanding of genetics, there will be better information on just what causes bodies to age. What Does This Mean for You?No matter which theory of aging is correct, or if instead aging is the total sum of several of these theories, the true bottom line is that aging is universal. Certain lifestyle factors may defer one's demise to a degree, and at the very least, offer a better quality to the quantity of a lifespan. A Word From VerywellFind ways to make living a healthy life fun. Gardening, foods, physical activity, relationships — they all support quality of life and may well extend its quantity too. Frequently Asked Questions
What are the biological theories of aging?Modern biological theories of aging in humans fall into two main categories: programmed and damage or error theories. The programmed theories imply that aging follows a biological timetable, perhaps a continuation of the one that regulates childhood growth and development.
Which biological theory of aging is related closely to the free radical theory?Mitochondrial theory of aging
These radicals then damage the mitochondria's DNA and proteins, and these damage components in turn are more liable to produce ROS byproducts.
Which of the following theories sees aging as a process whereby cells are assumed to have a limitation on the number of times they can reproduce to repair damage?Cellular Clock Theory: This theory suggests that biological aging is due to the fact that normal cells cannot divide indefinitely. This is known as the Hayflick limit, and is evidenced in cells studied in test tubes, which divide about 40-60 times before they stop (Bartlett, 2014).
What is the cellular clock theory of aging?Cellular clock theory of aging focuses on the lifespan of cells. Since many human cells do not continue to reproduce indefinitely, this theory suggests that aging is a result of cells hitting their programmed reproductive limit.
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