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توضیحات

 این یک مونوگراف تکمیل بوده که دارای پرپوزل هم میباشد شما میتوانید با پیام گذاشتن در وتسپ ما آن را دریافت کنید

وتسپ:۰۷۹۹۱۱۸۸۳۱

مونوگراف به صورت تضمینی بوده که نیاز به تغیرات ندارد و قبلا دفاع و ارایه شده است

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Chapter 1 : Definition of concepts

Definitions

Challenge

The definition of life has long been a challenge for scientists and philosophers.  This is partially because life is a process, not a substance.  This is complicated by a lack of knowledge of the characteristics of living entities, if any, that may have developed outside Earth.  Philosophical definitions of life have also been put forward, with similar difficulties on how to distinguish living things from the non-living.  Legal definitions of life have been debated, though these generally focus on the decision to declare a human dead, and the legal ramifications of this decision..At least 123 definitions of life have been compiled.

Descriptive

 Since there is no consensus for a definition of life, most current definitions in biology are descriptive. Life is considered a characteristic of something that preserves, furthers or reinforces its existence in the given environment. This implies all or most of the following traits:

1. Homeostasis: regulation of the internal environment to maintain a constant state; for example, sweating to reduce temperature.
2. Organization: being structurally composed of one or more cells – the basic units of life.
3. Metabolism: transformation of energy, used to convert chemicals into cellular components (anabolism) and to decompose organic matter (catabolism). Living things require energy for homeostasis and other activities.
4. Growth: maintenance of a higher rate of anabolism than catabolism. A growing organism increases in size and structure.
5. Adaptation: the evolutionary process whereby an organism becomes better able to live in its habitat.
6. Response to stimuli: such as the contraction of a unicellular organism away from external chemicals, the complex reactions involving all the senses of multicellular organisms, or the motion of the leaves of a plant turning toward the sun (phototropism), and chemotaxis.
7. Reproduction: the ability to produce new individual organisms, either asexually from a single parent organism or sexually from two parent organisms.

Physics

From a physics perspective, an organism is a thermodynamic system with an organized molecular structure that can reproduce itself and evolve as survival dictates. Thermodynamically, life has been described as an open system which makes use of gradients in its surroundings to create imperfect copies of itself. Another way of putting this is to define life as "a self-sustained chemical system capable of  undergoing Darwinian evolution", a definition adopted by a NASA committee attempting to define life for the purposes of exobiology, based on a suggestion by Carl Sagan This definition, however, has been widely criticized because according to it, a single sexually reproducing individual is not alive as it is incapable of evolving on its own. The reason for this potential flaw is that "NASA's definition" refers to life as a phenomenon, not a living individual, which makes it incomplete. Alternative definitions based on the notion of life as a phenomenon and a living individual have been proposed as continuum of a self-maintainable information, and a distinct element of this continuum, respectively. A major strength of this approach is that it defines life in terms of mathematics and physics, avoiding biological vocabulary.

Living systems

Others take a living systems theory viewpoint that does not necessarily depend on molecular chemistry. One systemic definition of life is that living things are self-organizing and autopoietic (self-producing). Variations of this include Stuart Kauffman's definition as an autonomous agent or a multi-agent system capable of reproducing itself, and of completing at least one thermodynamic work cycle.[28] This definition is extended by the evolution of novel functions over time.[29]

Death

Animal corpses, like this African buffalo, are recycled by the ecosystem, providing energy and nutrients for living organisms. Death is the termination of all vital functions or life processes in an organism or cell. One of the challenges in defining death is in distinguishing it from life. Death would seem to refer to either the moment life ends, or when the state that follows life begins.  However, determining when death has occurred is difficult, as cessation of life functions is often not simultaneous across organ systems. Such determination, therefore, requires drawing conceptual lines between life and death. This is problematic because there is little consensus over how to define life. The nature of death has for millennia been a central concern of the world's religious traditions and of philosophical inquiry. Many religions maintain faith in either a kind of afterlife or reincarnation for the soul, or resurrection of the body at a later date.

Viruses

Whether or not viruses should be considered as alive is controversial.  They are most often considered as just gene coding replicators rather than forms of life.  They have been described as "organisms at the edge of life"  because they possess genes, evolve by natural selection, and replicate by making multiple copies of themselves through self-assembly. However, viruses do not metabolize and they require a host cell to make new products. Virus self-assembly within host cells has implications for the study of the origin of life, as it may support the hypothesis that life could have started as self-assembling organic

  Definitional Skepticism

Nearly everybody agrees there is a distinction between life and non-life, typically understood as a difference in kind rather than one of degree. Furthermore, most people involved accept that life is some sort of natural kind, rather than a human psychological concept. That said, a common theme in recent philosophical work has been to express skepticism of life definitions as a goal. The literature on the definition of life is vast, repetitive, and utterly inconclusive. Philosophers have disagreed as to the ultimate source of the lack of consensus, citing unstated assumptions in either the definer’s approach or the question itself. Note that many scientists are less likely to be skeptical of the goal of defining life, though also more resistant to engaging in the philosophical debate.

One skeptical view has arisen from the observation that theoretical definitions of life presume a theory of life (Cleland and Chyba 2002, Benner 2010, Cleland 2019). Although it is not obvious that the authors allude to the theory-theory of concepts, described in section 1, a common analogy is to early chemical theory. According to this analogy, early alchemists likened the alchemists’ Aqua regia (“royal water”) and Aqua fortis (“strong water”). Development of atomic theory revealed, Cleland argues, that the true nature of water was H2O, while the other ‘waters’ were HNO3 + 3 HCl and HNO3, respectively. Cleland advocates avoiding definitions altogether, fearing they will blind us to new instances of life, and instead opts for tentative criteria, which she believes avoid the implicit dogma of even operational definitions.

خلاصه تحقیق

Life is a complex and multifaceted phenomenon, encompassing the state of being that distinguishes living organisms from inanimate matter. At its core, life is characterized by a set of essential attributes, including growth, reproduction, adaptation, metabolism, and response to stimuli. From the microscopic world of single-celled organisms to the vast diversity of flora and fauna populating ecosystems, life takes on myriad forms across the biological spectrum.

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