Search results
Results from the WOW.Com Content Network
Life functions through the specialized chemistry of carbon and water, and builds largely upon four key families of chemicals: lipids for cell membranes, carbohydrates such as sugars, amino acids for protein metabolism, and nucleic acid DNA and RNA for the mechanisms of heredity. Any successful theory of abiogenesis must explain the origins and ...
Birth is the act or process of bearing or bringing forth offspring, [1] also referred to in technical contexts as parturition. In mammals, the process is initiated by hormones which cause the muscular walls of the uterus to contract, expelling the fetus at a developmental stage when it is ready to feed and breathe.
Further, Eder, [20] in 1905, and Schaaf consider her work on silver chemistry [21] to be a landmark in the birth and early history of photography. [22] [23] Fulhame's work on the role of light sensitive chemicals (silver salts) on fabric, predates Thomas Wedgwood's more famous photogram trials of 1801. Fulhame did not, however, attempt to make ...
Preterm birth is the birth of an infant at fewer than 37 weeks gestational age. Globally, about 15 million infants were born before 37 weeks of gestation. [149] Premature birth is the leading cause of death in children under five years of age though many that survive experience disabilities including learning defects and visual and hearing ...
The history of life on Earth traces the processes by which living and extinct organisms evolved, from the earliest emergence of life to the present day. Earth formed about 4.5 billion years ago (abbreviated as Ga, for gigaannum) and evidence suggests that life emerged prior to 3.7 Ga. [1] [2] [3] The similarities among all known present-day species indicate that they have diverged through the ...
Energeticism – a theory that attempted to reinterpret all chemistry in terms of energy, rejecting the concept of atoms. Caloric theory – the theory that a self-repelling fluid called "caloric" was the substance of heat. Rendered obsolete by the mechanical theory of heat.
Host–guest chemistry encompasses the idea of molecular recognition and interactions through non-covalent bonding. Non-covalent bonding is critical in maintaining the 3D structure of large molecules, such as proteins and is involved in many biological processes in which large molecules bind specifically but transiently to one another.
In chemistry, racemization is a conversion, by heat or by chemical reaction, of an optically active compound into a racemic (optically inactive) form. This creates a 1:1 molar ratio of enantiomers and is referred to as a racemic mixture (i.e. contain equal amount of (+) and (−) forms).