Question: How many roles do molucules of chemical substances that constutute food play?
About the article "Biology", section "Energy".

Candidate passages:
The survival of a living organism depends on the continuous input of energy.
Chemical reactions that are responsible for its structure and function are tuned to extract energy from substances that act as its food and transform them to help form new cells and sustain them.
In this process, molecules of chemical substances that constitute food play two roles; first, they contain energy that can be transformed for biological chemical reactions; second, they develop new molecular structures made up of biomolecules.
The organisms responsible for the introduction of energy into an ecosystem are known as producers or autotrophs.
Nearly all of these organisms originally draw energy from the sun.
Plants and other phototrophs use solar energy via a process known as photosynthesis to convert raw materials into organic molecules, such as ATP, whose bonds can be broken to release energy.
A few ecosystems, however, depend entirely on energy extracted by chemotrophs from methane, sulfides, or other non-luminal energy sources.
Some of the captured energy is used to produce biomass to sustain life and provide energy for growth and development.
The majority of the rest of this energy is lost as heat and waste molecules.
The most important processes for converting the energy trapped in chemical substances into energy useful to sustain life are metabolism and cellular respiration.
A polyamine is an organic compound having two or more primary amino groups .
This class of compounds includes several synthetic substances that are important feedstocks for the chemical industry, such as ethylene diamine , 1,3-diaminopropane , and hexamethylenediamine .
It also includes many substances that play important roles in both eukaryotic and prokaryotic cells, such as putrescine , cadaverine , spermidine , and spermine .
As of 2004, there had been no reports of any geminal diamine, a compound with two or more unsubstituted groups on the same carbon atom.
However, substituted derivatives are known, such as tetraethylmethylenediamine, .
Piperazine is an example of a cyclic polyamine.
Cyclen and cyclam are examples of macrocyclic polyamines.
Polyethylene amine is a polymer based on aziridine monomer. 
A controlled substance is generally a drug or chemical whose manufacture, possession, or use is regulated by a government.
Controlled substances are substances that are the subject of legislative control.
This may include illegal drugs and prescription medications (designated Controlled Drug in the United Kingdom).
In the U.S., the DEA is responsible for suppressing illegal drug use and distribution by enforcing the Controlled Substances Act.
Some precursor chemicals used for the production of illegal drugs are also controlled substances in many countries, even though they may lack the pharmacological effects of the drugs themselves.
Substances are classified according to schedules and consist primarily of potentially psychoactive substances.
The controlled substances do not include many prescription items such as antibiotics.
Some states in the U.S. have statutes against health care providers self-prescribing and/or administering substances listed in the Controlled Substance Act schedules.
This does not forbid licensed providers from self-prescribing medications not on the schedules. 
Food chemistry's history dates back as far as the late 18th century when many famous chemists were involved in discovering chemicals important in foods, including Carl Wilhelm Scheele (isolated malic acid from apples in 1785), and Sir Humphry Davy published the first book on agricultural and food chemistry in 1813 titled "Elements of Agricultural Chemistry, in a Course of Lectures for the Board of Agriculture" in the United Kingdom which would serve as a foundation for the profession worldwide, going into a fifth edition.
In 1874 the Society of Public Analysts was formed, with the aim of applying analytical methods to the benefit of the public.
Its early experiments were based on bread, milk and wine.
It was also out of concern for the quality of the food supply, mainly food adulteration and contamination issues that would first stem from intentional contamination to later with chemical food additives by the 1950s.
The development of colleges and universities worldwide, most notably in the United States, would expand food chemistry as well with research of the dietary substances, most notably the Single-grain experiment during 1907-11.
Additional research by Harvey W. Wiley at the United States Department of Agriculture during the late 19th century would play a key factor in the creation of the United States Food and Drug Administration in 1906.
The American Chemical Society would establish their Agricultural and Food Chemistry Division in 1908 while the Institute of Food Technologists would establish their Food Chemistry Division in 1995.
Food chemistry concepts are often drawn from rheology, theories of transport phenomena, physical and chemical thermodynamics, chemical bonds and interaction forces, quantum mechanics and reaction kinetics, biopolymer science, colloidal interactions, nucleation, glass transitions and freezing/disordered or noncrystalline solids, and thus has Food Physical Chemistry as a foundation area. 
Major philosophical questions arise as soon as one attempts to define chemistry and what it studies.
Atoms and molecules are often assumed to be the fundamental units of chemical theory, but traditional descriptions of molecular structure and chemical bonding fail to account for the properties of many substances, including metals and metal complexes and aromaticity.
Additionally, chemists frequently use non-existent chemical entities like resonance structures to explain the structure and reactions of different substances; these explanatory tools use the language and graphical representations of molecules to describe the behavior of chemicals and chemical reactions that in reality do not behave as straightforward molecules.
Some chemists and philosophers of chemistry prefer to think of substances, rather than microstructures, as the fundamental units of study in chemistry.
There is not always a one-to-one correspondence between the two methods of classifying substances.
For example, many rocks exist as mineral complexes composed of multiple ions that do not occur in fixed proportions or spatial relationships to one another.
A related philosophical problem is whether chemistry is the study of substances or reactions.
Atoms, even in a solid, are in perpetual motion and under the right conditions many chemicals react spontaneously to form new products.
A variety of environmental variables contribute to a substance's properties, including temperature and pressure, proximity to other molecules and the presence of a magnetic field.
As Schummer puts it, "Substance philosophers define a chemical reaction by the change of certain substances, whereas process philosophers define a substance by its characteristic chemical reactions.
"Philosophers of chemistry discuss issues of symmetry and chirality in nature.
Organic (i.e., carbon-based) molecules are those most often chiral.
Amino acids, nucleic acids and sugars, all of which are found exclusively as a single enantiomer in organisms, are the basic chemical units of life.
Chemists, biochemists, and biologists alike debate the origins of this homochirality.
Philosophers debate facts regarding the origin of this phenomenon, namely whether it emerged contingently, amid a lifeless racemic environment or if other processes were at play.
Some speculate that answers can only be found in comparison to extraterrestrial life, if it is ever found.
Other philosophers question whether there exists a bias toward assumptions of nature as symmetrical, thereby causing resistance to any evidence to the contrary.
One of the most topical issues is determining to what extent physics, specifically, quantum mechanics, explains chemical phenomena.
Can chemistry, in fact, be reduced to physics as has been assumed by many, or are there inexplicable gaps?
Some authors Roald Hoffmann have recently suggested that a number of difficulties exist in the reductionist program with concepts like aromaticity, pH, reactivity, nucleophilicity, for example.
The noted philosopher of science, Karl Popper, among others, predicted as much.