The phospholipids readily self-assemble into the phospholipids bilayer that is considered the base component of the plasma membrane. The phospholipids have the interesting property of having a hydrophilic head and a hydrophobic tail, assemble into that “double” (thus “bi”)-layer, where the tails point inwards from both the inside and outside. To move material in or out of the cell, across the membrane, that is, active transport or passive transport must be used with the help of proteins to maintain the cellular processes of life.

Amphipathic molecules, for example the phospholipids among others, cause the fluidic properties of the cell membrane. The fluid mosaic model of the cellular membrane is one where many different components play their role in the “mosaic”, embedded or attached to the bilayer of phospholipids that form the base structure of the cell membrane. The hydrophobic and hydrophilic properties of the amphipathic molecules cause the transport of materials through the membrane. The membrane is said to be fluidic because it is not some static system: on the contrary, it is a dynamic process that is maintaining the internal energy of the system but is much weaker than covalent bonds (otherwise, it would require significantly more energy to pass materials in and out to correct hypotonic or hypertonic solutions in membrane diffusion).

Because of the loose, fluidic structure of the membrane, adjacent phospholipids can switch places with each other and others at about 107 times per second, meaning that phospholipids can travel two micrometers per second (the length of a bacterial cell). This dynamic composition of the membrane allows for protein drift, or the (slow, gradual) movement of proteins embedded in the membrane to another region of the membrane, sometimes driven by cytoskeletal fibers, and other times simply by the basic laws of diffusion (movement from an area of high concentration to an area of low concentration). The steroid cholesterol can be found wedged between various amphipathic molecules (such as phospholipids especially) and helps to make the membrane less fluid at warmer temperatures by making it more unlikely for the free-flow of phospholipids movement. The arrangement of cholesterol determines the changing permeability of the cell membrane with respect to temperature. Integral proteins are able to get inside the double layer and to the “core” segment where the hydrophobic tails of the phospholipids point. These “integral proteins” can sometimes stretch for the length of the membrane (thus the term, transmembrane proteins). The nonpolar amino acids of integral proteins can, for example, assist in extracellular interaction as well as produce changes in the cytoplasm within the cell membrane (an “integral” part of cell communication). The surface of the cell membrane hosts peripheral proteins, sometimes merely as exposed components of integral proteins. Proteins like bacteriohodopsin serve as transportation mechanisms to moderate material transport in and out of the cell membrane, contributing to the function of the membrane.

The selective permeability of the cell membrane is determined by temperature, protein composition, and the influences of the internal cytoplasmic organelles and other chemical systems. By communicating through intercellular joining (gap junctions, tight junctions), the inner components of the cell may transmit commands (via physical protein structures) to acquire or “accept” various resources, say more calcium if that is what is determined needed by the genome of the organism. The permeability of the cell is to a large degree moderated by peripheral proteins, integral proteins, and steroids, which moderate the functioning of the surface of the membrane as well as the internal processes (i.e., whether the fluidity of the phospholipids is to be preserved). The hydrophobic properties of the inside layers of the cell membrane make it a slow journey any charged atom or particle to cross the membrane. Polar molecules (glucose, sugars, etc.) pass only slowly, and hydrophilic molecules cannot normally pass (unless assisted by, say, innermembrane proteins).

Transport proteins can be found embedded in the fluid mosaic plasma membrane. They assist in the transport of materials in and out of the membrane. Their shapes are specifically changed when in contact with their target substances. Shape is specific to targets to transport.

The concentration gradient means that concentration is moving from an area of higher concentration to an area of lower concentration. The law of diffusion states that this will occur, that there is energy enough to move the substances to the areas of lower concentration. It is considered to be potential energy because energy is converted from the concentration to some sort of kinetic or transportation-based energy as the molecular materials flow down the concentration gradient and convert the potential energy into kinetic energy.

A hypertonic solution is one in which the concentration of solutes is greater outside of the cell than it is inside the cell. An isotonic solution is when the concentration of the solutes is equal on both sides of the cell membrane. The hypotonic solution is where the percentage of solutes in the cytoplasm is greater than the percentage of solutes in the environment. And when that occurs you are going to get a constant in flux of water into the cell.

Concentration gradients are changed to regulate whether or not the cell is immersed in hypertonic, hypotonic, or isotonic solutions. By causing a hypotonic solution to exist water flows into the cell, increasing the water levels. By causing a hypertonic solution, water flows out from the cell, and the cell shrinks in size. Too much of either cytolysis and plasmolysis will cause cellular decay (death). Cell walls assist in keeping the cell membrane from growing much too large, sort of like isolating it from too adversely affecting the surrounding tissue.

Diffusion is the movement of material from an area of higher concentration to an area of lower concentration. Transport proteins are specific to certain types of materials (`shape recognition') and assist in forming pathways through the cellular membrane to allow for the movement of substances in and out of the cell. Transport proteins then assist in diffusion by actively transporting substances.

The first step in cellular communication is transmission. This is where some sort of hormone message, neuro-electrical message, or enzyme-based (local) message is generated. The second step is in reception of the message. The message then travels down the signal-transduction pathway and causes specific cellular response to the specific stimulus (the message). An example of resulting behavior is muscle contraction upon neural signaling to the nearby motor neurons.

The multiple steps in the signal transduction pathway provide for more variation in possible responses to possible messages. The provision of reusable components and steps means that more specific responses can be generated and developed throughout species of cells. Also, there generally is no single-step process anywhere in biology to begin with, as cellular communication would not be then possible, since there must be specific steps in order to respond to a stimulus, to be able to come up with some behavior that is selected by the specific message. The message is not necessarily the resulting behavior.

The three major parts of the neuron include the dendrite, the axon, and the cellular body. Dendrites are short and stumpy and receive molecular messages. The axons transmit the messages onwards. The body of the cell converts dendrite messages to axon messages.

A reflex is a learned response by the body and does not go to the brain, i.e., in humans (true) reflexes stop around the spinal cord and the nervous tissue in that location. An example of a reflex arc is one wherein some adult human moves closer and closer to some hot substance without prior knowledge, and after touching it, quickly pulling it away. The fingers would transmit an overpowering message of `pain' that would cause the nervous tissue to respond by selecting specific motor neuronal signaling that would quickly move the hand back and warn the rest of the nervous tissue (at least the appropriate nervous tissue stored in the cranial cavity).

The membrane potential is on the axon as the active potential is being transmitted to the next cell by traveling towards the synapse. The resting potential is the charge of the axon due to the influx of sodium ions and the outflux of calcium ions, creating a negative charge, waiting for the next active potential to come across.

The central nervous system is composed of the brain and spinal cord. The peripheral nervous system is composed of sensory neurons and motor neurons. Sensory are the receptors. Motor are the performers.

Very little is known about human consciousness or even if what people call `consciousness' really exists. It is no doubt helpful to character mass behavior as `consciousness', however, it is also evident that particular stimulation and neural firing patterns in the brain contribute to some extent the passing of signaling from lower regions of the brain to higher regions of the brain, where further processing is done in order to select from behaviors and responses.

Proximate questions concern those immediate stimulating factors of the environment that trigger responses in an organism. These proximal questions are usually “how” questions”. The opposite sort of behavior concerns “ultimate questions” and they address the evolutionary significance of some behavior, i.e., why do these organisms fit together in these specific ways?

Innate behavior is based on the organism's behavioral genotype. The environment provides stimulation causing influence upon the behavior of the organism (not in the case where innate responses are stimulated).

Ethologists say that fixed action patterns (FAPs) are sequences of unlearned behavioral acts that are largely unchangeable and once initiated, usually carried out to its completion. An example of this act is that of fish behavior observed by Tinbergen. Tinbergen saw that stickleback fishes attack others near their nests that have red underbellies. In fact, the sign stimulus turns out to be some sort of red underbelly on any oncoming object. And in humans, coughing is another fixed action pattern. Once the feeling comes about, it becomes increasingly difficult to resist the coming cough.

The action of an organism brings it into environments and specific situations where they can potentially come to harm and reduce their reproductive viability. And sometime they come into situations where their behavior increases reproductive success in number of organisms produced. Thus, behavior contributes to the life history of an organism which is specifically selected (or, rather, “not killed without reproducing”). Adaptations or changes in innate behavior with respect to time limit the possible responses an organism can have to their environment and this can lead to death, less reproductive viability, and so on.

The optimal foraging theory says that there is a compromise between feeding costs and feeding benefits. Each organism must metabolize materials in order to utilize the energy to get even more energy. Should they mess up and not use the energy effectively to obtain more energy, they will die. The classic example of an opportunistic feeder is crows and their ascent through the air to drop clams onto the ground in an attempt to obtain more food. There is an optimal balance between flight height and energy replenishing that can be found and over the course of evolutionary history, behaviors traditionally have etched closer and closer to that optimal method. (Note: variability in clam shell hardness also factor, as well as many other things influencing the behavior of the crows).

Learning is, by definition, the modification of behavior itself based off of experiences. For example, the ability to learn a language is one particular function of the complex brain in some particular context due to the human genome. Maturation is the continuing development of the neuromuscular system and can change innate behaviors over time as muscular control becomes more refined. Habituation is the loss of responsiveness to some stimuli and thus will remove a possible response to that particular stimuli. The creation of new responses is often termed synthesis.

Imprinting is learning that is limited to a specific time period in an animal's life and is generally irreversible. The sensitive period is of major importance because that is the period in which learning of behaviors and possible responses can take place. An example of imprinting is the mother and child relationship found throughout goats, cats, rabbits, etc. Usually, without the right scent, the mother will reject the newborn. And invariably the young will have an imprinted memory of the scent of the parent, or some other symbol that the organism is the one where food can become obtained and so on. The young bird of the white-crowned sparrow does not sing for the first 50 days, however, it spends its time memorizing the song of its own species by listening to the other members of the population sing. Interestingly, sparrows can use this template even when listening to tape recordings in labs. Sparrows at the end of their sensitive period have this tendency to then attempt to sing their songs and match it to the memorized template such that they can harmonize properly. Thus, complex vocal maneuvers can be completed without many millions of proteins being triggered and developed over many thousands of generations of songbird.

Classical conditioning involves some particular response and an association formation with some particular reward or pain. Operant conditioning is trial and error learning where repetition of behavior is learned (or in some cases, to not repeat the behavior).

The ultimate bases of learning Is play, behavior that has no apparent goal and according to the practice hypothesis largely assists in developing cognitive motor control and so on. The exercise hypothesis takes on more validity in that it says that play is more for cardiovascular exercise and muscular system in use.

Kinesis is a (simple) change in activity in response to a stimulus. This means that the moth that sees a light moving towards it is a kinesis, whereas the baby that cries upon seeing a scary man, is not. Taxis is an automatic movement towards or away from the stimulus. An example would be the cricket that randomly jumps away upon significant change in visual input data. Landmarks are objects in the spatial view of an organism and can be used to moderate behaviors, for example, the honeybees that use landmarks to return visit the most lucrative flowers. Cognitive maps are internal representations (patterns) showing where objects are, in relation to other objects. For example, the human brain constructs a cognitive map of the environment in which it is put and gets significantly concerned when there is significant change (i.e., “there was a door here”). Migration is long-term behavior that moves an organism from one area of geography to another, i.e., birds flying south for the winter.

Agnostic behavior is a contest in which there are threats and submissions to be made in the hopes of obtaining access to some particular resource or mate. An example of agnostic behaviors can be found in species of dogs that show their teeth and pose specifically to look directly in their opponent's eyes. Within populations of organisms with agonistic behaviors, there is an established dominance hierarchy, meaning that, say, a group of chickens will peck at each other until they know who knows is more overpowering than the others, etc. Top ranked chickens are then assured access to necessary resources (food). Territories are regions of land that individuals defend, such as the bull sea lions that defend small territories used only for mating.

Courtship significantly depends on the species in question, some species being more successful when there is one-to-one mating and apparently that provides the offspring better chance of survival and moving on to reproduce on their own. And in other cases, such as in some insects, it is more beneficial to eat the male mate and use the material for laying eggs, and allowing the eggs to eat through the material once they hatch. Courtship encourages parental investment.

The acts of mating and birth in species that use internal fertilization is temporally separated and thus the influential act of mating on the development of the species would not encourage paternal involvement in the birth of the offspring.

Communication requires a signal and an organism to initiate the signal in response to whatever stimuli the organism encountered. The lifestyle of the organism influences the mediums in which signals can travel. The production of such signals is influenced by the morphological characteristics of the organism, i.e., an organism without any way of making sound is not going to be using sound as a method of communication (although it is remotely possible for some mute animal to use noise-making as a method of communication, though no specific examples come to mind to prove my point fallacious).

Honeybees dance around in attempt to communicate information. The round dance indicates nearby food. The waggle dance indicates food in some distant direction and just how far it might be. Some suspect that pheromones and sound can be conveying information about the location and sort of food found by the dancing honeybee.

The concept of altruism states that animals sometimes do things that reduce individual viability but increase species viability. The coefficient of relatedness concerns the probability that an individual in the population has the same gene as the organism in question. This effectively means that similar genes will attempt to protect similar genes when played out on a large enough time scale, or at least that genes that result in protein structures and systems that protect and promote the similar genes will be the one that are protected. This is why brothers may tend to help out each other when in trouble yet despise one another at any other time.

Hamilton's rule is that natural selection favors altruism if the number of recaptures in the second catch per the total number in the second catch is equivalent to the number marked in the first catch per the total population N. The process of favoring altruistic behavior that enhances the reproductive success of relatives of the particular genotype is known as kin selection.

Sociobiology operates on the premise that certain behaviors are characteristic products (phenotypes) of genome data being selected over time through natural selection.

Sensation is caused by stimulation. Perception is the information processing of the sensation.

The general functions include the transmission of signals from the dendrites towards the cell bodies and afferent neurons transmit signals towards the central nervous system. Those neurons that transport signals away from the central nervous system are called the efferent neurons and function as information transmission cells that pass on signals towards more peripheral nervous system cells. The nervous system generally gathers information, transmits, processes, and finally sends the information to other parts of the animal body.

The eyecups of Planaria are small and not incredibly specific. The associated neural pathways are more sensitive to light changes than to any sort of `sharp details'. The compound eyes of insects overlap each other in vision significantly and arrange the visual input such that the insect has nearly maximal vision of its environment. The insect is more susceptible to very small changes in the visual input, since they are easily startled and must have some sort of quick jump reflex as an innate behavior (taxis). Mollusks have larger eyes and are able to focus in on particular objects, and in fact, some mollusks (think squid, octopus) are able to differentiate between colors and particular objects thanks to the information processing of their nervous systems.

Rods are more susceptible to night-time light input and the cones are more susceptible and functional for daylight vision. Cones are susceptible to three major differences in wavelengths and thus are also the main functional components in differentiating between colors. Cones quickly integrate signals whereas rods slowly integrate the data.

An aquatic environment

A terrestrial environment

Air

The three functions of the skeleton include (1) structural support, (2) locomotion support, and (3) connective support. The structural support provides for the consistency of the structure of the organism and the connective support is different in that it `wires' the organs and systems together upon the one skeletal system—it would be even more complicated to have multiple interconnective systems. The locomotion support provides for the movement of the organism and impact management just like automobiles have shock-pads to optimize the smoothness of the ride.

Hydrostatic skeletons are functional due to the fact that the pressures of waters on either side of the material provide for the maintained consistency of the structure and thus can be considered skeletal. On terrain these systems are ineffective because of the air pressure on the external side of the skeleton at least at some point (maybe not immediately, perhaps after epithelial layers). Air pressure is not necessarily the same as water pressure that an aquatic species of organism has developed with over millions of generations.

The strength of the exoskeleton is provided in part by the proteins that are secreted in the extracellular matrix keeping all of the cells closely together and less easily broken off from the rest of the tissue. Flexibility is provided in that the arthropods are divided into segments and between these segments there is the possibility for the said flexibility—otherwise the body segments would not easily be usable at all because they would have to match the statically placed exoskeleton providing only length-wise movement (this is obviously not the case, arthropods with exoskeletons do have tendencies to move in various directions in quick bursts and not only straight in direction).

In endoskeletal systems the muscle arrangement is within the body barrier (skin system) and in exoskeletal systems the muscles must be closer to the exoskeletons meaning that they are tightly tucked under the skeleton but not deeply within the body, meaning that the muscles are basically “one” layer down from the exoskeleton. This provides for movement by pushing against the exoskeleton and thusly moving along the rest of the body. In endoskeletal animals the muscle arrangement is due to the evolutionary history of the species where members reproduced more with muscles in places that provided the most reproductive benefit.