In general it means breakdown (lysis) to equal pieces (homo = same) There are separate meanings for the word in chemistry and biology.

Homolysis in chemistry

In chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

, homolysis (from Greek ὅμοιος, homoios, "equal," and λύσις, lusis, "loosening") or homolytic fission is chemical bond
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

 dissociation of a neutral molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

 generating two free radicals. That is, two electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

s that are involved in the bond are distributed one by one to the two species. Each of the two covalently shared (see covalent bond
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....

) electrons are withdrawn by the bonded atoms.
A−B → A• + B•

Such reactions can be induced by irradiation in the UV region, diffused sunlight or peroxide. High temperatures in the absence of oxygen (pyrolysis
Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. It involves the simultaneous change of chemical composition and physical phase, and is irreversible...

) can also induce homolytic elimination of carbon compounds.

The energy involved in this process is called bond dissociation energy
Bond dissociation energy
In chemistry, bond-dissociation energy or D0, is one measure of the bond strength in a chemical bond. It is defined as the standard enthalpy change when a bond is cleaved by homolysis, with reactants and products of the homolysis reaction at 0 K...

. Bond cleavage is also possible by a process called heterolysis
In chemistry, heterolysis or heterolytic fission is chemical bond cleavage of a neutral molecule generating a cation and an anion. In this process the two electrons that make up the bond are assigned to the same fragment...


Homolysis in biology

In biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

homolysis means that dividing cell gives two equal-size daughter cells.
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