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Aging is therefore presumed to be a byproduct of evolution, but why mortality should be selected for remains a subject of research and debate. Programmed cell death and the telomere "end replication problem" are found even in the earliest and simplest of organisms. [35] This may be a tradeoff between selecting for cancer and selecting for aging ...
Overview of signal transduction pathways involved in apoptosis. Cell death is the event of a biological cell ceasing to carry out its functions. This may be the result of the natural process of old cells dying and being replaced by new ones, as in programmed cell death, or may result from factors such as diseases, localized injury, or the death of the organism of which the cells are part.
Biological immortality (sometimes referred to as bio-indefinite mortality) is a state in which the rate of mortality from senescence (or aging) is stable or decreasing, thus decoupling it from chronological age. Various unicellular and multicellular species, including some vertebrates, achieve this state either throughout their existence or ...
The cells do not reproduce in synchrony without explicit and continual prompting (as in experiments with stalked bacteria [9]) and their exponential phase growth is often not ever a constant rate, but instead a slowly decaying rate, a constant stochastic response to pressures both to reproduce and to go dormant in the face of declining nutrient ...
The following outline is provided as an overview of and topical guide to concepts related to infectious diseases in humans.. Infection – transmission, entry/invasion after evading/overcoming defense, establishment, and replication of disease-causing microscopic organisms (pathogens) inside a host organism, and the reaction of host tissues to them and to the toxins they produce.
Mortality is the number of deaths, in a particular group, over a specific time period. [46] There are two types of mortality: intrinsic and extrinsic mortality . Intrinsic mortality is defined as mortality due to ageing, the physiological decline due to innate processes, whereas extrinsic mortality is the result of environmental factors such as ...
Conversely, premature death can refer to a death that occurs before old age arrives, for example, human death before a person reaches the age of 75. [78] Animal and plant cells normally reproduce and function during the whole period of natural existence, but the aging process derives from the deterioration of cellular activity and the ruination ...
Bacteria function and reproduce as individual cells, but they can often aggregate in multicellular colonies. [54] Some species such as myxobacteria can aggregate into complex swarming structures, operating as multicellular groups as part of their life cycle , [ 55 ] or form clusters in bacterial colonies such as E.coli .