Search results
Life is a quality that distinguishes matter that has biological processes, such as signaling and self-sustaining processes, from matter that does not. It is defined descriptively by the capacity for homeostasis, organisation, metabolism, growth, adaptation, response to stimuli, and reproduction. All life over time eventually reaches a state of ...
- Overview
- Definitions of life
- Metabolic
- Physiological
- Biochemical
life, living matter and, as such, matter that shows certain attributes that include responsiveness, growth, metabolism, energy transformation, and reproduction. Although a noun, as with other defined entities, the word life might be better cast as a verb to reflect its essential status as a process. Life comprises individuals, living beings, assignable to groups (taxa). Each individual is composed of one or more minimal living units, called cells, and is capable of transformation of carbon-based and other compounds (metabolism), growth, and participation in reproductive acts. Life-forms present on Earth today have evolved from ancient common ancestors through the generation of hereditary variation and natural selection. Although some studies state that life may have begun as early as 4.1 billion years ago, it can be traced to fossils dated to 3.5–3.7 billion years ago, which is still only slightly younger than Earth, which gravitationally accreted into a planet about 4.5 billion years ago. But this is life as a whole. More than 99.9 percent of species that have ever lived are extinct. The several branches of science that reveal the common historical, functional, and chemical basis of the evolution of all life include electron microscopy, genetics, paleobiology (including paleontology), and molecular biology.
The phenomenon of life can be approached in several ways: life as it is known and studied on planet Earth; life imaginable in principle; and life, by hypothesis, that might exist elsewhere in the universe (see extraterrestrial life). As far as is known, life exists only on Earth. Most life-forms reside in a thin sphere that extends about 23 km (14 miles) from 3 km (2 miles) beneath the bottom of the ocean to the top of the troposphere (lower atmosphere); the relative thickness is comparable to a coat of paint on a rubber ball. An estimated 10–30 million distinguishable species currently inhabit this sphere of life, or biosphere.
Much is known about life from points of view reflected in the various biological, or “life,” sciences. These include anatomy (the study of form at the visible level), ultrastructure (the study of form at the microscopic level), physiology (the study of function), molecular biology and biochemistry (the study of form and function at chemical levels)...
Metabolic definitions are popular with biochemists and some biologists. Living systems are objects with definite boundaries, continually exchanging some materials with their surroundings but without altering their general properties, at least over some period of time. However, there are exceptions. There are frozen seeds and spores that remain, so far as is known, perfectly dormant. At low temperatures they lack metabolic activity for hundreds, perhaps thousands, of years but revive perfectly well upon being subjected to more clement conditions. A candle flame has a well-defined shape with a fixed boundary and is maintained by “metabolizing” its organic waxes and the surrounding molecular oxygen to produce carbon dioxide and water. Similar reactions, incidentally, occur in animals and plants. Flames also have a well-known capacity for growth. These facts underscore the inadequacy of this metabolic definition, even as they suggest the indispensable role of energy transformation to living systems. (See metabolism.)
Britannica Quiz
Physiological definitions of life are popular. Life is defined as any system capable of performing functions such as eating, metabolizing, excreting, breathing, moving, growing, reproducing, and responding to external stimuli. But many such properties are either present in machines that nobody is willing to call alive or absent from organisms, such...
A biochemical or molecular biological definition sees living organisms as systems that contain reproducible hereditary information coded in nucleic acid molecules and that metabolize by controlling the rate of chemical reactions using the proteinaceous catalysts known as enzymes. In many respects, this is more satisfying than the physiological or metabolic definitions of life. However, even here there are counterexamples. Viruslike agents called prions lack nucleic acids, although the nucleic acids of the animal cells in which they reside may be involved in their reproduction. Ribonucleic acid (RNA) molecules may replicate, mutate, and then replicate their mutations in test tubes, although by themselves they are not alive. Furthermore, a definition strictly in chemical terms seems peculiarly vulnerable. It implies that, were a person able to construct a system that had all the functional properties of life, it would still not be alive if it lacked the molecules that earthly biologists are fond of—and made of. (See biochemistry.)
Students save 67%! Learn more about our special academic rate today.
Learn the various meanings and uses of the word life as a noun and an adjective, from the quality of a living being to the duration of a person's existence. See synonyms, examples, etymology, and related phrases of life in the online dictionary of Merriam-Webster.
Learn about the basic properties of life and the challenges of defining it. Explore the traits of organization, metabolism, and homeostasis that all living things share.
- do we have dna same as our parents?It's not exactly the same, we take roughly 50% from each. Also the expression of those genes can vary and some may be changed by factors such as DN...
- why are viruses hard to cureBecause, most of the antibiotics, infect the bacteria through destroying their cell wall. Whereas Viruses insert their genetic material into a huma...
- What are examples of Unicellular organisms?There are five groups of unicellular organisms: bacteria, archaea, protozoa, unicellular algae, and unicellular fungi
- How does the ability to evolve define whether one living thing is alive? Evolution only occurs becau...The qualities of living things are synthesis, transport, excretion, regulation, nutrition, growth & development, respiration, and reproduction. I a...
- In the "Is this the definitive list?" section, if the offspring of a female horse and a male donkey ...Hinny is a stallion and a female donkey Jenny is female horse and a male donkey
- All living organisms have "organized" cells. What do you mean by "organized". It's described very br...By the term "organized", they meant the way the cells are "positioned" in the body of an organism. Similar to how bricks make up a wall, cells make...
- Does something have to be able to reproduce to be Alive? For example, a living creature becomes infe...No, reproduction is a defining, but not all-inclusive trait of living beings. That is, not all beings need to reproduce to be considered living, bu...
- If viruses are not considered alive organisms, how can they be so dangerous and reproduce them so fa...Viruses can hijack our cell's DNA to program it to make more copies of the virus. Though viruses themselves contain no DNA and are technically not...
- Do we know for sure that we are the only conscious organism?It is a matter of debate. No, we are not the only species which could think, dream or feel, https://www.nationalgeographic.com/news/2015/07/150714-...
Learn the meaning and usage of the word LIFE, which can refer to the condition, state, or principle of living things, or to a specific period or aspect of existence. Find synonyms, related words, idioms, and quizzes about life on Dictionary.com.
- 2 min
Mar 3, 2018 · The meaning of life is that which we choose to give it, not that which we are given by God or an afterlife. Human life can have a purpose, even in the most absurd, painful, and dispiriting of circumstances, and we can choose to create our own meaning or purposes. The article explores the arguments for and against the existence of God, the purpose of life, and the role of meaning in human psychology and culture.
May 15, 2007 · 3. Naturalism. Recall that naturalism is the view that a physical life is central to life’s meaning, that even if there is no spiritual realm, a substantially meaningful life is possible. Like supernaturalism, contemporary naturalism admits of two distinguishable variants, moderate and extreme (Metz 2019).
