E2science

God is in the details. God is found in details that collude to create the bosom of reality each soul nestles into. Notice the bare sliver of chance by which nature succeeds, seemingly against the odds. Still, nature racks up win upon win, compounded until the Earth meets her destiny cradling the only known sentient life-form in the universe. The creationists are right. They are right but for one large supposition. The Earth, in all its sublime detail purportedly existing for man's delight alone, was not created for us. We were created for it. It is an ongoing process, stacking millennium upon millennia.

Terra appears more and more fragile as humanity learns where, when, and how it exists in the universe. Seemingly minor details, too numerous to completely detail here, become intrinsic to life's existence when properly understood. Limit the number of factors to just five and still science can paint a picture of the Earth happening at just the right place, at just the right time, and well, at just the right everything.

Sol

Humanity would have no solar system at all without it; the Sun displays special traits that cause it to be the perfect planetary-system incubator. A much larger star was first necessary to till the field, so to speak. It burned hot and it burned fast.(F) Our Sun's progenitor fused elements together, starting with the fusion of helium from hydrogen fuel, much as the Sun does today. But it also created most of the elements that make up our planet before reaching iron, and a critical juncture in its stellar life.* When the star exploded, the Sun and all of the planets eventually coalesced from the resulting debris. The smaller star that formed to be the center of our solar system inhabits a perfect Goldilocks balance, providing just the right amount of energy for billions of years. Considering that complex life evolved only recently in our planet's history**, one can surmise that complex life needs billions of years to develop.

Jupiter

Jupiter exists as the big brother in our system. As a very protective brother, Jupiter uses its massive gravity well to attract and repel large fast-moving bodies from the inner solar system. Our solar system has an asteroid belt kept strictly in line around the Sun in an orbit between Mars and Jupiter. Only occasionally does Earth see the epoch-changing impacts from large asteroids or comets. While Earth's formative years saw it pummeled with objects from space that contained among other things, water, today's Earth last saw a devastating impact around 65 million years ago.(B)

It may well have been Jupiter that sent a Mars-sized object on a collision course with the third rock from the Sun. After this violent event a moon approximately a quarter of Earth's size orbited the third planet.*** Such a large ratio between planet and moon is rare; the Earth and Moon can be regarded as a binary-planet, rotating around a barycenter three-quarters of the way out from Earth's center. In what is surely a team-effort, the Moon provides a stabilizing force on Earth in a number of different ways. Stability is good for life.

Moon

So what if a lifeless rock rotates around us, providing nocturnal illumination and tidal forces while still controlling the moods of half the human population every 29.5 days.(C) What could this seemingly useless sphere of green cheese offer life?

The Giant Impact Hypothesis is the theory du jour in moon-evolution circles.(G) To summarize, the theory supposes that a proto-planet the size of Mars collided with the Earth, forming a very unique planetary system. The Earth before the moon rotated much faster, and only slowed down because of the drag created by its new satellite. Picture an ice-skater, spinning rapidly, that slows down as she extends her arms out to her sides, and you can visualize how the Earth went from a 6-hr to 24-hr day.(I)

Bah! So the Earth would have shorter days, so what?

Without the moon, Earth's magnetic field would be four times stronger as its iron core's rotational speed would be four times faster. While this means that we would have that much more protection from the Sun's harmful radiation, evolution would be four times hindered by not being exposed to those energies that drive mutation, and thus evolution.(I) If 6-hr days**** don't bother you, and even regular 100 mph (161 kmh) winds fail to bring you down, then deadly hurricane force winds will have to do the trick.

Double bah! As I once said upon the island of Isla Nublar, 'Life finds a way', even without moderate winds. Or lysine. Or windy lysine.

Continuing on, then. The moon's stabilizing force provides a regular, if changing, axis around which our planet rotates. Chaotic climatic changes, resulting from wild shifts in the Earth's axis sans lunar gravity, prevent regular cycles and seasons from occurring. A climate defined by geographical boundaries would not exist, leaving evolution without the necessary time to drive life's development.

Bah upon your... Oh wait, that sounds pretty bad; worse than being accosted by a T-Rex while sitting atop the potty. Trust me, I'm in a unique position to judge these matters.

The Moon was once much closer to Earth.(C) The proximity created much larger tides that rushed inland and out, covering hundreds of miles twice each day. It is possible that a much greater amount of organic materials mixed and were concentrated by cyclic deluge and evaporation, allowing for a better chance for a greater diversity of life to form. Admittedly, this imagery brings to mind a vast planetary soup with life seething in the briny foam.

Iron Core

Space is dangerous, far from being the empty place we envision when we consider it a cold vacuum. In fact, space is filled with a veritable ether of energies and even gases. Most of the energy is quite caustic to life. We only benefit from a very limited exposure to a limited set of energy frequencies.

Thankfully the Earth has at its center a very hot, rotating iron-core. This core casts a protective magnetic blanket around earth, acting exactly like a force-field that blocks most of what the Sun and the rest of the universe throws at us.(D) Without the magnetic field, a day at the beach is more likely to resemble Sarah Connor's nuclear nightmare from Terminator. Like Sarah says, "There is no future except the... Oh noes.. My face is meltingggrwwhAAAHHH!!"

Water

The blue in our marble points to the fact that Earth is a watery planet. The shared history of Earth-life and Earth-water is such that one history hinges entirely upon the other. No water, no life (as we know it). Our extraterrestrial searches illuminate just how rare and significant Earth's abundant water supply is. In fact, we have not yet found a planet with this selfsame feature. We also have not found complex life on any other planet. Coincidence? Maybe.

More than simply being life's creator, water exists as a very unique molecule. Water is polar; it has a different positive and negative charge at each pole. This quality translates to a greater solvency in the chemical world. Ions are attracted to these charges, which means that the small salty oceans humans carry inside themselves can transport things like oxygen and sugars throughout the body. Water's characteristic surface-tension is responsible for capillary action, which moves water and nutrients through the roots of plants and tiny human capillaries.(J)

Water is transparent, and solid water floats in liquid water. Transparency means that sunlight can propagate through water, allowing photosynthesis to occur at greater depths. The fact that ice floats means that we don't have sinking ice crushing water-borne life, instead it forms a barrier at the water's edge. Hydrogen-bonding and water's relatively light weight of 18 grams-per-mole both work to create water's high specific heat index.(J) Generally, this means that water exists as a liquid for a large range of temperatures. Liquid water is good for life.

So what?

It is obvious to most that four of the five factors discussed here are in fact contingent upon each other for their own place in and on planet Earth. The house of cards seems to pile higher and wobble precipitously. But it is our human senses, experience, and thus perspective that creates in us a trepidation at knowing just how special our Pale Blue Dot is. Whether your picture of the universe allows a place for an epic photo-bomb from god or not, rest assured that the laws of the universe are not easily muted. While one piece of the puzzle seems stacked upon the other in a Jenga tower, the resulting structure has stood the test of time and there is little reason to doubt that life will continue. Some form of the Earth will be around to be swallowed up by the Sun in its gasping death throes, some five billion years in the future.(E)

Still, the self-destructive tendencies of the human species have yet to be fully explored, so stay tuned.

   * Our Sun is thought to be a third-generation star and our entire solar system is made of the recycled star stuff of previous star generations.(A)
  ** Simple animals have only been on this planet for the past 600 million years of a 4.5 billion year history, while single-celled organisms have been playing the evolution game for 3.8 billion years. Mammals have only been a part of the scene for 200 million years.(K)
 *** A ring of debris orbits the planet, and in an amazingly short amount of time -- about one day -- it begins to coalesce into a satellite. It takes somewhere between 1 and 100 years for the Moon to gather most of the stuff into a ball.(C)
**** One estimate puts the day-length at 8-hrs, without the Moon, at our present point in the planet's timeline(I)

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A. http://solarsystem.nasa.gov/yss/display.cfm?Year=2010&Month=11&Tab=Background
B. http://www.sciencedaily.com/releases/2010/03/100304142242.htm
C. http://www.space.com/scienceastronomy/moon_mechanics_0303018.html
D. http://geology.about.com/od/core/a/about_the_core.htm
E. http://www.enotes.com/science-fact-finder/space/when-will-sun-die
F. http://en.wikipedia.org/wiki/Stellar_evolution
G. http://en.wikipedia.org/wiki/Giant_impact_theory
H. The Universe: Season 4, Episode 2: The Day the Moon Was Gone
I. http://www.astrosociety.org/education/publications/tnl/33/moon2.html
J. http://ga.water.usgs.gov/edu/waterproperties.html
K. http://en.wikipedia.org/wiki/Timeline_of_evolution

"Copperhead" can refer to two extremely distinct species of snake, to the North American Agkistrodon Contortorix, a member of the Crotalinae (pit viper) subfamily; or to Austrelaps, a genus of venomous elapid snakes native to the relatively fertile temperate southern and eastern part of the Australian continent. As of now, the Austrelaps spp. are another writeup for another day. This writeup will address only the Agkistrodon species of North America.

Adult copperheads usually grow to a total length of 50-95 cm, although some specimens have exceeded 1 m. Males are usually larger than females. The maximum reported length for the subspecies A. c. mokasen is 134.6 cm. Likewise, the maximum reported length for A. c. controtrix is 132.1 cm.

The body is relatively stout, and the head is broad and distinct from the neck. Because the snout slopes down and back, it usually appears less blunt than that of the cottonmouth, A. piscivoris. Owing to this, the top of the head usually extends further forward than the mouth.

The scalation includes 21-25 (with an average of 23) rows of dorsal scales at midbody, 138-157 ventral scales in both sexes, and 38-62/37-57 subcadual scales in males/females. The subcaudals are usually single, but the percentage thereof decreases clinically from the northeast, where about 80% are undivided, to the southwest of the geographic range where as little as 50% may be undivided. On the head there are usually 9 large symmetrical plates, 6-10 supralabial scales and 8-13 sublabial scales.

The color pattern consists of a pale tan to pinkish tan ground color that becomes darker toward the midline, overlaid with a series of 10-18 crossbands. These crossbands are light tan to pinkish tan to pale brown in the center, but darker towards the edges. They are about 2 scales wide or less at the midline, but expand to a width of 6-10 scales on the sides of the body. They do not extend down to the ventral scales. Often, the crossbands are divided at the midline and alternate on either side of the body, with some individuals even having more half bands than complete ones. A series of dark brown spots is also present on the flanks, next to the belly, and are largest and darkest in the spaces between the crossbands. The belly is the same color as the ground color, but may be a little whitish in part. At the base of the tail there are 1-3 (usually 2) brown crossbands followed by a gray area. In juveniles, the pattern on the tail is more distinct: 7-9 crossbands are visible, while the tip is yellow. On the head, the crown is usually unmarked, except for a pair of small dark spots, one near the midline of each parietal scale. A faint postocular stripe is also present; diffuse above and bordered below by a narrow brown edge.

Common names for the snakes of the Agkistrodon family include: Copperhead, chunk head, death adder, highland moccasin, dry moccasin, narrow-banded copperhead, northern copperhead, pilot snake, poplar leaf, red oak, red snake, southeastern copperhead, white oak snake, American copperhead, southern copperhead, and cantil cobrizo.

The copperhead is found in the majority of the Southern United States, including Texas, Oklahoma, Kansas, Missouri, Arkansas, Louisiana, Mississippi, Alabama, Georgia, Florida, South Carolina, North Carolina, Tennessee, Kentucky, Virginia, West Virginia, Illinois, Indiana, Ohio, Iowa, Pennsylvania, Maryland, New Jersey, Delaware, New York, Connecticut and Massachusetts. In Mexico it occurs in Chihuahua and Coahuila.

Within its range it occupies a variety of different habitats. In most of North America it favors deciduous forest and mixed woodlands. It is often associated with rock outcroppings and ledges, but is also found in low-lying swampy regions. In the states around the Gulf of Mexico, however, this species is also found in coniferous forest. In the Chihuahuan Desert of west Texas and northern Mexico, it occurs in riparian habitats, usually near permanent or semipermanent water and sometimes in dry brooks.

A. contortrix is currently classified as Least Concern (LC) on the IUCN Red List of Threatened Species. Species are listed as such due to their wide distribution, presumed large population, or because it is unlikely to be declining fast enough to qualify for listing in a more threatened category.

Roughly 90% of the copperhead diet consists of small rodents, such as mice and voles. On observation and in captivity, they have also shown fondness for large insects and frogs, and though mainly a terrestrial snake, they have been known to climb trees to gorge on emerging cicadas. Like all pit vipers, A. contortrix is generally an ambush predator. It will assume a promising position and wait for sutible prey to arrive. One exception to ambush foraging occurs when copperheads feed on insects. When hunting insects, copperheads will actively pursue their prey.

In the southern United States, they are nocturnal during the hot summer months, but are commonly active during the day during the spring and fall. Like most North American viperids, these snakes prefer to avoid humans, and given the opportunity will leave the area without biting. However, unlike other viperids they will often "freeze" instead of moving away, and as a result many bites occur from people unknowingly stepping on or near them. This tendency to freeze likely evolved because of the extreme effectiveness of their camouflage. When lying on dead leaves or red clay they can be almost impossible to notice. They will frequently stay still even when approached closely, and will generally strike only if physical contact is made.

Copperheads breed in late summer, but not every year: sometimes a female will produce young for several years running, then not breed at all for a time. They give birth to live young about 20 cm long: a typical litter is 4 to 7, but it can be as few as one or as many as 20. Their size apart, the young are similar to the adults, but lighter in color, and with a yellow-marked tip to the tail, which is used to lure lizards and frogs. Studies have shown that male A. contortrix has longer tongue fork tine length than females during the breeding season to aid in chemoreception of males searching females.

Although venomous, these snakes are generally non-aggressive and bites are almost never fatal. Copperhead venom has an estimated lethal dose of around 100 mg. Copperheads often employ a "warning bite" when stepped on or agitated and inject a relatively small amount of venom, if any at all. "Dry bites" involving no venom are particularly common with the copperhead, though all pit vipers are capable of a dry bite. Bite symptoms include intense pain, tingling, throbbing, swelling, and severe nausea. Damage can occur to muscle and bone tissue, especially when the bite occurs in the outer extremities such as the hands and feet, areas in which there is not a large muscle mass to absorb the venom. A bite from any venomous snake should be taken very seriously and immediate medical attention sought, as allergic reaction and secondary infection are always possible.

The venom of the Southern copperhead has been found to hold a protein called "Contortrostatin" that halts the growth of cancer cells and also stops the migration of the tumors to other sites. It will probably be ten or more years before contortrostatin is used in practical treatment but it has shown to be a very promising drug in laboratory studies.

Although technically the antivenin CroFab could be used to treat an envenomation, it is usually not administered for copperheads, as the risk of complications of an allergic reaction to the treatment are greater than the risk from the snakebite itself in most cases. The very few reported deaths from copperhead bites all involved multiple snakes. Pain management, antibiotics, and medical supervision in the case of complications is usually the course of action.

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Due to the somewhat technical nature of this writeup, I should note that the entire thing was shamelessly reworked from an old paper I wrote, entitled "An Overview of Agkistrodon Contortorix", with many changes made to reduce the overall length. In reworking, I tried to make it extremely accessible to everyone, but there are some terms (for instance, terms describing types of scalation, like supralabial and subcadual) that are necessary. I apologize for any inconvience.

A Computer Tomography scan (CT or CAT for short), is an X-Ray test that produce cross sectional images of the body parts scanned. These cross sections allow radiologists to inspect the inside of the body, just like one could inspect the insides of a bread by slicing it.

CT scans are more often used to evaluate the condition of the brain, neck, spine, chest, abdomen, pelvis and sinuses.

When scanning the abdomen or pelvis regions, the patient is required to drink a dilute barium liquid, which works as a contrast agent to help the radiologist to identify the gastrointestinal tract, and detect abnormalities with the organs.

Using modern technology, the cross sections produced by a CT scan can also be fed to a volumetric renderer, that generates a 3D model of the area scanned, in which the examiner can move freely around.

LINE-1 retrotransposons are sections of DNA which are capable of copying themselves into another part of the genome. Although traditionally considered to merely epitomize the concept of the selfish gene, more recently they have been suggested to have physiological functions. Here I discuss the incredibly fascinating hypothesis that LINE-1 retrotransposons may be important in generating neuronal variation.

Selfish genes and retrotransposons

Personally, I think that there's something problematic about Dawkins' reductionism in his book The Selfish Gene. In that book, Dawkins explains that the gene can be considered as the smallest unit of selection, in which case the "purpose" of every single gene is to independently copy itself as far as it can. We are vehicles for our genes, who share a common interest - the organism - in order to propagate themselves.

Don't get me wrong, I agree that it's practically a truism to say that genes that can contribute to their own survival will as a result be better at replicating. My problem is with the conceptualisation of genes as monads. Dawkins seems to believe that the survival of the organism can be calculated as the sum of its genes.

The most important lesson of developmental biology has been that there is no function without context. I can't elaborate too much at this point, but suffice to say that in the same way that it would be impossible to read an alien language without some sort of reference, and in the same way that a protein could not be assigned a function without a cellular context, so too a gene has no survival-index without the context of its host organism, (and taking a step further back, without the context of its host organism's environment).

It is now interesting to consider unique cases like transposons. Transposons are segments of DNA which are capable of "jumping" around the host organism's genome. A category of transposon are the retrotransposons, which are segments of DNA which jump around the genome by copying themselves and then inserting the copy into another part of the genome. Transposons, including retrotransposons are often considered to be classical selfish genes. They don't seem to contribute to the organisms well-being at all, and their entire purpose is to replicate as much as possible irrespective of the organism.

As you can probably guess, the picture is far more interesting that all that. But first I need to say a few words about different aspects and mechanisms of variation in neurons.

Neuronal variation

It's common when trying to communicate the incredibility of the human brain to quote the number of neurons, or the number of connections, and then to try and quantitatively compare that with an electronic computer. That's all well and good, but it's not enough. Discussing the brain as a network of nodes connected in parallel ignores the complexity of that system. It ignores the manner in which individual neurons process information inputs, how that processing affects future processing, and the type of signals involved. It also ignores the fact that neurons are not a homogeneous population. There are various convenient ways to differentiate neurons, for instance their morphology, what receptors they present, what neurotransmitters they use to signal, and so forth.

An extraordinary diversity is found within the neuronal population. There might be as many as 10,000 types of neuron, although the definition of neuronal type is debated. Diversity exists between individual cells within a neuronal subtype, highlighting the importance of single neurons in the network. Even neurons with a similar morphology can differ in important molecular details, expressing different combinations of ion channels, for instance, providing cells with various excitation thresholds and distinctive firing patterns. However, how and when neuronal diversity is generated remains unknown. (Muotri & Gage 2006)

This complexity is presumably required by the brain in order to manifest its higher-order capacities, including perhaps self-awareness. Different mechanisms are responsible for generating the neuronal variation, including alternative transcription start sites and RNA splicing. Retrotransposition may also contribute to neuronal variation.

L1 and somatic mosaicism

The next paragraph, and the next paragraph alone, depends on evidence heard second hand; my "source" heard Fred Gage give a talk. Gage is a leader in this particular sub-field, and is the primary investigator on almost all of the papers referenced for this writeup.

The story begins with Fred Gage and colleagues studying neuronal precursor cells. These are cells that aren't quite neurons yet, but can mature into the various forms of neurons. As part of their experiments the group sequenced their cells, but something strange kept occurring: the more times these precursor cells divided the bigger their genomes got! After ruling out some sort of contamination, they took at look at what the cells were transcripting, and realised that these cells had a lot of retrotransposon activity. In particular, the retrotransposon called Long interspersed repetitive element-1, which abbreviates to LINE-1 which abbreviates to L1.

The very first paper showing that L1 could contribute to neuronal heterogeneity was published in 2005 in the prestigious science journal Nature. The paper demonstrated that when precursor cells begin to transform into neurons, they reduce the amount of Sox2 (transcription factor). Sox2 normally binds to the DNA near L1 elements to prevent them from copying themselves, so when there is less Sox2 then there is increased L1 retrotransposition. This seems to be a phenomenon restricted somewhat to neuron development, and might involve those precursor cells remodeling their chromatin (DNA) to alter L1 availability. Finally, the paper demonstrated the L1 is active during neuron development in actual animals.

Big deal? Yes. First of all, the facts until now had said that transposon activity is only present in germ line cells (ie. those that produce sperm and ovum), but is soon turned off. This paper shows that normal cells have the potential for transposon activity, and more-so, that neurons preferentially allow it! It also implies that even inside the same brain, different areas are not completely genetically identical. Different neurons may have experienced different transposon activities, in which L1 was copied a different number of times and to different locations in the genome. And as a consequence, where those L1 insertions affect genes, the actual neurons' gene activity may differ.

These results were followed up with publications reporting that L1 is similarly active in humans, and can even be found in adult brains, although it's not yet clear whether how this relates to adult neurogenesis (Coufal 2009); a third paper elaborated on the molecular mechanisms involved in L1 activation (Moutri 2010).

L1, the brain, and life

If valid, the implications of physiological retrotransposition in neurons could be huge. I stress "physiological" because that would imply that this feature of neuronal development has been selected for. If that were the case it would highlight the fact that although transposons considered in and of themselves display a parasitic function,without regard for their host, this is not the whole story. L1 as a DNA parasite, and L1 as a mechanism for variation are both "selfish". They both result in increasing the capacity of L1 to propagate. The difference is whether we call L1 selfish in its capacity as a gene, or as an organism. Because I hold that genes have no meaning, no natural function, without their host context, I'd suggest that only the second possibility is meaningful.

Even in a perfectly controlled experiment some animal traits, like fear and learning, appear to display an unavoidable variation. This variation results in the well known bell curve response, and has been termed intangible variance. This intangible variance might be partially explained by appealing to L1: "L1-mediated retrotransposition could be a mechanism that alters neuronal function in individuals, thereby broadening the spectrum of behavioral phenotypes that can originate from any single genome" (Singer 2010).

One of the most incredible thing about people is how much they vary. (The other incredible thing is obviously their similarity). It seems so obvious and commonsensical that people should be tweaked slightly differently in myriad ways that we don't question it. Even when identical twins have differences we're only mildly distracted, after all, each person is their own person. But maybe not. Maybe it is this inherent fallible randomness that makes us possible - that transforms us from an anonymous ego into a particular you and me.

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Some other things that spring to mind as possibly being applicable to L1-mediated neuronal variance: adult neurogenesis, anti-depressants, and neuronal pruning during early development.

References:

• Muotri AR et al. Somatic mosaicism in neuronal precusor cells mediated by L1 retrotransposition (2005) Nature
• Muotri AR & Gage FH Generation of neuronal variability and complexity (2006) Nature
• Coufal NG et al. L1 retrotransposition in human neural progenitor cells (2009) Nature
• Ma DK et al. Epigenetic choreographers of neurogenesis in the adult mammalian brain (2010) Nat Neuro
• Muotri AR et al. L1 retrotransposition in neurons is modulated by MeCP2 (2010) Nature
• Singer T et al. LINE-1 retrotransposons: mediators of somatic variation in neuronal genomes? (2010) Trends Neuro

Conflict of interest: None. I have not been associated with any of the authors cited. (Nov 2010).

 

Introduction

 

This writeup is about the meaning of the word ion as it is definied in physics and chemistry. In these sciences, an ion is essentially a charged atom or molecule. This means the particle has either one or more extra electrons, or is missing one or more electrons. If it is missing electrons, it is called a cation, and is positive; if it has extra electrons, it is called an anion and is negative.

 

Properties

 

One of the most obvious things about an ion is that it is charged. As such, it is affected by electric fields. This means, for instance, you can accelerate it in a particle accelerator. It also means that cations and anions attract each other. As such, it is almost impossible to have a clump of cations in one place and a clump of anions in another, because the electric force is overwhelmingly strong. If you were to take for instance one gram of table salt, split it in sodium cations and chloride anions, and put them on opposite sides of a spoon, the the electric force between them would be around 10²⁰ Newton, which is comparable to the force that keeps the earth in her orbit. As such, separating significant numbers of charges is pretty much impossible, and ionic matter is largely mixed evenly. This is called quasi-neutrality.

Apart from this rather impressive physical property, there is also a chemical change. Because the chemical properties of an atom or molecule are determined by the electrons surrounding the nucleus, having extra or missing electron makes the particle "behave" as a different atom chemically. For instance, a fluorine cation has one extra electron. As such, it has the same number of electrons a neon, a noble gas. This configuration is chemically quite stable. As such, fluorine, and many other substances, are often or almost always found in this ionic form.

 

Occurence

 

Where do we find ions? Well, pretty much all over the place. I'll summarize three places where ions are commonly found

 

1. In a salt: A salt is defined as a substance that consists of ions. Table salt is just one example of a salt. Salts are typically formed when a substance that easily loses electrons, such as a metal, meets a substance that easily accepts them, such as a halogen or an organic compound. Because of the strong ionic bonds, salts are quite stable; most have very high melting points.
2. In a polar solvent: Some salts can dissolve in polar solvents, such as water. These dissolved ions are called electrolytes. In the human body, these electrolytes play a crucial role.
3. In a plasma: Plasmas are essentially energetic gases, in which some of the molecules are split in ions and free electrons. Most of these ions are cations; anions are more rare, as the plasma is so energetic the free electron state is preferable.

It is interesting to note that both the solution and the plasma are decent to good conductors of electricity. If a salt is melted, it will conduct electricity as well.

 

 

Conclusion

This is no more than a short and condensed summary on what an ion is; one could probably spent a lifetime researching ions. The most salient features are that they have an electrical charge, which changes their physical behavior. Furthermore, the extra electrons change the chemical behavior. Ions are essential for biological processes.