Homeostasis
The concept of homeostasis—that living things maintain a constant internal environment—was first proposed in the 19th century by the French physicist Claude Bernard, who stated that “all important mechanisms, as they differ, are only There is one thing: that of constantly maintaining the conditions of life.”
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Britannica Quiz
Science Quiz
As originally conceived by Barnard, homeostasis applies to an organism’s struggle for survival. This concept was later expanded to include any biological system, from the cell to the entire biosphere, living things in all regions of the Earth.
Unity
Cells Animal cells and plant cells are composed of membrane-bound organelles, including a distinct nucleus. In contrast, bacterial cells do not have organelles.
All organisms, regardless of their individuality, share certain biological, chemical and physical characteristics. For example, all are composed of basic units called cells and the same chemical substances, which, upon analysis, reveal remarkable similarities, even in organisms as different as bacteria and humans. Furthermore, since the function of any organism is determined by the way its cells interact, and since all cells interact in the same way, all organisms have the same basic function.
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Not only is there unity of basic living beings and functions, but also the unity of origin of all living beings. According to a theory proposed by German pathologist Rudolf Virtue in 1855, “All living cells arise from preexisting living cells.” This theory seems to hold true for all living organisms at the present time under current environmental conditions. If, however, life originated on Earth more than once in the past, then the fact that all organisms have the same basic structure, composition, and function indicates that only one original type succeeded.
A common origin of life would explain why humans or bacteria—and all life forms in between—have the same chemical substance, deoxyribonucleic acid (DNA), in the form of genes, the ability of all organisms. causing it to replicate itself perfectly. and passing genetic information from parent to offspring. Moreover, the mechanisms of this transmission follow a pattern that is the same in all organisms.
Whenever a change (mutation) occurs in a gene, there is some kind of change in the organism that contains the gene. This is the universal phenomenon that gives rise to differences (variations) in the population of organisms from which nature selects for survival those who are best able to cope with the changing conditions in the environment.
Evolution
Types of natural selection
Types of natural selection. Downward arrows point to phenotypes against which selection acts. Stabilizing selection (left column) works against phenotypes at both extremes of the distribution, favoring the multiplication of intermediate phenotypes. Directional selection (center column) acts against only one extreme of the phenotypes, causing a shift in the distribution toward the other extreme. Divergent selection (right column) acts against intermediate phenotypes, producing a distribution in the distribution toward each extreme.
In his theory of natural selection, which will be discussed in more detail later, Charles Darwin proposed that “survival of the fittest” was the basis of organic evolution (the change of living things over time). Evolution itself is a biological phenomenon common to all living things, even though it has led to their differences. Evidence supporting the theory of evolution comes primarily from the fossil record, comparative studies of structure and function, studies of embryonic development, and studies of DNA and RNA (ribonucleic acid).
Diversity
Despite the basic biological, chemical, and physical similarities found among all living organisms, the diversity of life exists not only among species but also within each natural population. The study of the phenomenon of diversity has a long history because many variations in nature are visible to the eye. The fact that organisms changed in prehistoric times and that new variations are constantly evolving can be confirmed by paleontological records as well as laboratory breeding experiments. Long after Darwin assumed that mutations existed, biologists discovered that they were caused by changes in the genetic material (DNA). This change can be a minor change in the sequence of DNA components (nucleotides), a major change such as a change in the structure of a chromosome, or a complete change in the number of chromosomes. In any case, a change in the genetic material in reproductive cells manifests itself as some kind of structural or chemical change in the offspring. The outcome of such a mutation depends on the interaction of the mutant offspring with its environment.
It has been suggested that sexual reproduction became the dominant type of reproduction among organisms because of its inherent advantage of variability, the mechanism that enables a species to adapt to changing conditions. New mutations are likely present in genetic variants, but the extent to which mutations become significant in the gene pool depends on the number of offspring with mutants or variants (assortative reproduction). It is possible for a genetic novelty (new variation) to spread to all members of a population over time, especially if the novelty increases the population’s chances of survival in the environment in which it exists. Thus, when a species is introduced into a new habitat, it either adapts to the change through natural selection or some other evolutionary mechanism or eventually dies out. Because each new habitat implies a new adaptation, habitat changes have been responsible for millions of different species and for heterogeneity within each species.
The total number of extant animal and plant species is estimated to be between 5 million and 10 million. About 1.5 million of these species have been described by scientists. The use of taxonomy as a means of creating some kind of order among the astonishing number of different kinds of living things appears as early as the Book of Genesis—the references to cattle, beasts, birds, reptiles, trees, etc. from The first scientific attempt at classification, however, is attributed to the Greek philosopher Aristotle, who sought to establish a system that would indicate the relationship of all things to one another. He arranged everything along a scale, or “ladder of nature,” with nonliving things at the bottom. Plants were placed below animals, and humanity was at the top. Other schemes that have been used to group species include major physical similarities, such as fins or feathers, which indicate natural relatedness, and also similarities in reproductive structures.
The taxonomy is based on two major assumptions: one is that similar physical structure can be used as a criterion for taxonomic grouping; Second, in addition to structural similarities, evolutionary and molecular relationships between organisms can be used as a means to determine taxonomy.
Behavior and interpersonal relationships
The study of the relationship of organisms to each other and to their environment is known as ecology. Because these interactions are so important to the Earth’s well-being and because they can be seriously affected by human activities, ecology has become an important branch of biology.
Continuity
Whether an organism is a human being or a bacteria, its ability to reproduce is one of the most important characteristics of life. Because life comes only from pre-existing life, it is only through reproduction that successive generations can continue the characteristics of a species.
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