An Antibody is a large protein molecule which latches on to and neutralizes foreign invaders such as bacteria and viruses. Each antibody acts only on a very specific target molecule, known as an antigen. (It can also coat microbes in a way to make them palatable to scavenger cells such as microphages.)Read More
Some biological patterns are cyclical and function as clocks, subject to resetting and breakdown. The Circadian rhythms ( the term means approximately daily and was coined by Franz Halberg in 1951) are an examply of biological cycles which are non-linear oscillators, which mesh with day/night cycles. They are subject to entrainment or synchronization because of their time-dependent sensitivity. Exposed to some standard disturbance beginning at different times in the cycle, there will be different phase shifts inflicted. (see Winfree, 1987. p. 12) There is a particular point of vulnerability, where circadian rhythms can break down or become unpredictable when subject to a particular stimulus known as the "critical annihilating stimulus". This arrhythmic center in the pattern of timing is called its "phase singularity"Read More
While genes are usually thought to entail some direct causal consequence in the expression of a character, a central tenet of genetics is that a mutant locus or the normal allele does not "control a character," but is only a differential. The production of a character involves many genes.Read More
In coevolutionary processes, the fitness of one organism or species depends on the characteristics of the other organisms or species with which it interacts, while all simultaneously adapt and change." At every moment natural selection is operating to change the genetic composition of populations in response to the momentary environment, but as that composition changes it forces a concommittent change in the environment itself.Read More
One of the most important issues in the premodern biology of the 18th century was the struggle between preformationist and epigenetic theories of development. The preformationist view was that the adult organism was contained, already formed in miniature, in the sperm, and that development was the growth and solidification of this miniature being. Preformationists assumed that the germs of all living beings were preformed and had been since the Creation. Preformationism sought to maintain and secure--against the irritation posed by the complexity of organic phenomena--the claim for a thorough and rational determination of the material world.Read More
Is there an independent problem of form, for which biology must develop its own concepts and methods of thought? The Pre-Darwinian project of rational morphology was to discover the "laws of form," some inherent necessity in the laws which governed morphological process. It sought to construct what was typical in the varieties of form into a system which should not be merely historically determined, but which should be intelligible from a higher and more rational standpoint. (Hans Driesch, 1914, p. 149)Read More
The immune system is engaged in a process of somatic selection. It is constantly distinguishing foreign molecules or bacteria, viruses, and even another person's skin from the molecules of an individual body, or soma. The well-spring of immunologic defense is scattered through the body in the tissues and organs of the lymphatic system and is carried out by a set of proteins called antibodies. The ultimate target of all immune responses is an antigen, which is usually a foreign molecule from a bacterium or other invader.Read More
At cell division, or mitosis, the nucleus of the cell divides. Each chromosome within the nucleus is first duplicated, and one copy passes to each daughter nucleus, and hence to each daughter cell.Read More
One way of explaining regulation is to think of cells being able to obtain positional information as to where they are and to use that information in development. This way, cells can be moved about and interchanged (in experiments or accidents) without disturbing the developmental process. Gradient fields could be one source of positional information. (see also morphic fields) For Lewis Wolpert, "positional information is about graded properties" measured with reference to a "coordinate system." Wolpert's simple "French flag" model appealed to the "non-mathematical but theoretically minded." A gradient described as a straight inclined line, could have threshold points translating into patterns (eg red, white, and blue). But "just what moves this answer beyond the realm of tautology remains obscure." Evelyn Fox KellerRead More
The term symbiosis was defined by the German mycologist Anton De Bary (1879) as meaning the "living together" of "dissimilar" or "differently named" organisms.
Today, in most current biological literature, it is taken to mean "mutualistic biotrophic associations" (biotrophy: one partner requires a nutrient that is a metabolic product of the other partner.) For example, lichens consist of algal and fungal components in nearly equal mass in symbiosis.
B-cells are formed in the bone marrow, and provide humoral immunity mediated by antibodies. They can recognise parts of antigens free in solution, by fitting them to the antibodies they carry on their surface. When a particular B-cell come into contact with an antigen which it fits, the B-cell swells and divides (through mitosis, or clonal selection)and the new activated B-cells (Plasma cells) secrete antibodies proteins that attack the invader. Once activated, a B-cell can pump out more than 10 million antibody molecules per hour. The antibodies neutralize or precipitate the destruction of the antigens by complement enzymes or scavenger cells. The B-cell can also produce different isotypes of the antibodies, who fit the same antigen but who defend the body in different ways.Read More