The physical processes necessary for primitive life are the ingestion of substances, converting these substances into useable forms of nutrient and chemical energy, and the expelling of waste product. Given a proper medium and habitat the lower forms of life carry out their metabolic processes in a manner that can be termed as homeostatic. The homeostatic state is designated as the area in between the objects above and below the horizontal line.
Chemotaxis, stress, and symbiotic relationships are precursors to systems of neurological states of pain and joy. 
If all life on earth originated from a single root on the phylogenetic tree of life, further understanding will validate how neural systems of pain and joy evolved from within the earliest forms of life on earth.[14]

The term Pain is to be described as an impairment of genetically governed norm or standard rates of metabolism. Likened to hunger, thirst, sensations of hot or cold as we experience them, a cell or organism can be thought of experiencing pain when there is a deficiency of substances or environmental phenomena necessary to maintain the cell or organism functional at the genetically governed, predetermined rates of metabolism, i.e. homeostasis. Pain is an exigent inefficiency of genetically governed norm or standard rates of metabolism; or a sense of insufficiency, or an excess of substance or phenomena necessary for sustaining or maintaining a genetically induced given rate of metabolism within an organism or cell. Responses of an organism or cell to the sensation of pain can be growth, locomotion, or any activity, e.g. particular cellular biochemical feedback mechanisms being idiosyncratic events a cell or organism reacts with as it seeks to maintain or sustain genetically predetermined norm or standard rates of metabolism.

An example of a pain stimulus and a metabolically induced cellular response would be a plant receiving ten hours of sunlight a day and growing strong. Supposing a tree falls now and blocks the path of direct sunlight to the plant. The plant could be thought of as experiencing pain. The homeostatic rate of metabolism of the plant has been impaired, and the response of the plant may be to grow in height or breadth seeking levels of metabolism of the past. 

Another example would be to imagine a paramecium subjected to a saline environment. The response of the paramecium to the painful saline stimulus upon its cellular wall may be to cause more energy to be used for locomotion, seeking an environment more compatible. This increased energy response of locomotion in a matured organism is also painful since the organism or cell initially lacks or needs that which it seeks to grow or re-establish.
The mature state of an organism or cell is defined as one with fully developed organelles, given a mode average of organelles per life span of a given number of organisms or cells.
The photosynthetic experiments of Theodor Engelmann (1882)[15] brought aggregations of bacteria upon Cladophora chloroplasts absorbing the blue and violet (410, 430, 453 nm) and red (642, 662 nm) wavelengths of light. The Cladophora chloroplastic organelle evolved out from and maintain cellular homeostasis within an aquatic environment inclusive to the entire range of radiated energy emitted from the sun. The metabolic processes of the Cladophora chloroplastic organelle are inferred by myself to then operate most efficiently, thus have preference for ("enjoy") a medium involving the particular blue, violet, and red wavelengths of light.

A cellular state of Joy is to be defined as an excess of phenomena, substances, or biological activity necessary to keep the genetically governed norm or standard rates of metabolism at the homeostatic level. Joy on a cellular level involves one or many organelles brought to function with more efficiency within the organism or cell. This said stimulus and efficiency of function brought to bear on one or many organelle may or may not be immediately contrary to homeostasis.
Joyful stimuli initiate no recognized metabolically triggered responses within the cell or organism which seek resumption for the previous condition of homeostasis.
The symbiotic relationship of algae and jellyfish are modalities of the joyful stimulus and response. Other examples of joy are best exemplified with artificial descriptions, such as placing a plant in an environment to receive direct sunlight twenty-four hours a day, or placed within an environment where the atmosphere is ninety-seven percent carbon dioxide. Such a joyful stimulus may be to some plants the condition to exploit and thrive without stress. Other plants will begin to reduce cellular activities and metabolic processes necessary for a homeostatic condition to exist so as to be more efficient with the system of cellular activities the plant reacts with while in the presence of an abundance of sunlight or carbon dioxide.

The consequence of a joyful stimulus upon the homeostatic metabolic activities of the cell resolves the cell to adapt, modify, or alter its normal metabolic processes in acceptance of the new metabolic activity a joyful stimulus causes within the cell or organelle. Joy initiates metabolic responses that attempt to incorporate the metabolic activity intrinsic to the joyful stimulus to that with homeostasis. Cellular metabolic responses of joy play to the resiliency of the relationship between organelles that maintain homeostasis.

At the cellular level, the pain—joy spectrum of stimuli introduces two basic modes of cellular responses. With a painful stimulus the cell or organism is active more then less metabolically, and if physically potential, seeking towards previous levels of homeostasis. Moderate stimuli of pain initiates within cells genetically predetermined responses to metabolically re-establish levels of homeostasis within the environment.

If homeostasis should be disrupted within the cell because of moderate joyful stimulus, said organelle’s biochemical functions cascade and fluctuate outside of a proper, homeostatic relationship with other organelles. If said joyful stimulus were to remain constant upon the cell, these cascading and fluctuating cellular activities will eventually exhaust the resources and vitality of the organelle(s) as (an) integral member(s) of the cell. Viable homeostasis being given as the norm, maintaining said joyful stimuli sustains organelle / cellular dysfunction.
Two types of environmental stimulus disrupt the homeostatic condition of the single cell. The response of the cell to any stimulus disrupting homeostasis being one of only two courses of metabolic activity which an observer will then use to determine whether a painful or a joyful stimulus to the cell has occurred.
Should stimulus and response of pain or joy within an organism or cell become metabolically intolerable, the destruction of the organism or cell results. These two finite states of cellular endurance are signified by the small, perpendicular vertical segments at the end of the arrows of the horizontal line.
From the observation of cellular activity of any species of life one could not logically conclude that the internal metabolic functions, processes, and systems that maintain homeostasis at the cellular level exist to cause the eventual destruction of said life. That is, for example, the metabolic processes at the cellular level of any species primarily function and exist creating compositions of poisons and toxins to later metabolically trigger and release upon its larger biological structures. There are organelles in some cells with a capacity to enable the cell itself to self-destruct. The capacity to do so is there, yet the cellular homeostatic metabolic process is not logically or truthfully observed to possess and conduct a nature of sabotage, or to possess a self-destructive tendency onto the entire biological system within which it resides. On the contrary, the metabolic process seeks continuum or a preservative quality upon itself. Given homeostasis for the ideal, optimal condition of the cell, the metabolic process can then be said to have placed a value on its self: the value concept called Preservation, or Life. A subjective, normal and internal quality that the metabolic process has placed upon its self.
The two parameter pain and joy system allows methods for delineation describing the physical condition a life form acquires or possesses at any given moment.
Also, for completeness, viral properties possess complex chemical structures that interact and manipulate specific outside environments. Their category, at the top of the chemical catalysts and or as the primary forms of life, remains undefined.
Acknowledging natural selection as a valid process for the continuation of species, the breakdown of metabolic processes that eventually cause the cell and the organism to whither and cease to function as a biological system is an imperfection that leads to the next picture illustration.