is the methodical study of nature including testable explanations
. From classical antiquity
through the 19th century, science as a type of knowledge was more closely linked to philosophy
than it is now and, in fact, in the Western world
, the term "natural philosophy
" encompassed fields of study that are today associated with science, such as astronomy
, medicine, and physics
. However, during the Islamic Golden Age
foundations for the scientific method
were laid by Ibn al-Haytham
in his Book of Optics
. While the classification of the material world by the ancient Indians
into air, earth, fire and water
was more philosophical, medieval Middle Easterns
used practical, experimental observation
to classify materials.
Today, the ever-evolving term "science" refers to the pursuit of knowledge, not the knowledge itself. It is often synonymous with "natural and physical science" and often restricted to those branches of study relating to the phenomena of the material universe and their laws. Although the term implies exclusion of pure mathematics, many university faculties include Mathematics Departments within their Faculty of Science. The dominant sense in ordinary use has a narrower use for the term "science." It developed as a part of science becoming a distinct enterprise of defining the "laws of nature"; early examples include Kepler's laws, Galileo's laws, and Newton's laws of motion. In this period it became more common to refer to natural philosophy as "natural science." Over the course of the 19th century, the word "science" became increasingly associated with the disciplined study of the natural world, including physics, chemistry, geology and biology. This sometimes left the study of human thought and society in a linguistic limbo, which was resolved by classifying these areas of academic study as social science. For example, psychology evolved from philosophy, and has grown into an area of study.
Currently, there are both "hard" (e.g. biological psychology) and "soft" science (e.g. social psychology) fields within the discipline. As a result, and as is consistent with the unfolding of the study of knowledge and development of methods to establish facts, each area of psychology employs a scientific method. Reflecting the evolution of the development of knowledge and established facts and the use of the scientific method, Psychology Departments in universities are found within: Faculty of Arts and Science, Faculty of Arts, and a Faculty of Science. Similarly, several other major areas of disciplined study and knowledge exist today under the general rubric of "science", such as formal science and applied science.
refers to a collection of processes by which a cell
identifies and corrects damage to the DNA
molecules that encode its genome
. In human cells, both normal metabolic
activities and environmental factors such as UV
light can cause DNA damage, resulting in as many as 1 million individual molecular lesions
per cell per day. Many of these lesions cause structural damage to the DNA molecule and can alter or eliminate the cell's ability to transcribe
that the affected DNA encodes. Other lesions induce potentially harmful mutations
in the cell's genome, which affect the survival of its daughter cells after it undergoes mitosis
. Consequently, the DNA repair process must be constantly active so it can respond rapidly to any damage in the DNA structure.
The rate of DNA repair is dependent on many factors, including the cell type, the age of the cell, and the extracellular environment. A cell that has accumulated a large amount of DNA damage, or one that no longer effectively repairs damage incurred by its DNA, can enter one of three possible states: an irreversible state of dormancy, known as senescence; cell suicide, also known as apoptosis or programmed cell death; or unregulated cell division, which can lead to the formation of a tumor that is cancerous.
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