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What is osmosis?
This is the process by which water moves from one side of a semi-permeable (lets some substances through, like water, but not others, like the dissolved salts) to the other. Solutions of different osmotic pressures will become "balanced" if left alone for a time, as the water molecules move from the side of greater concentration of water (hence, less salty) to the other side of lesser concentration of water (or, more salty).
A organism is said to be hypotonic (lesser balance) when the internal body fluid is not as salty as the surrounding water medium.
On the other hand, it is said to be hypertonic when the internal fluid is saltier than the surrounding water medium.
When the internal body fluid is the same saltiness as the external medium, those 2 fluids are said to be isotonic.
The osmotic pressure of a solution (very difficult to measure) can be computed from the freezing point depression for that solution. This is possible as the salts that increase osmotic pressure depresses the freezing point of that liquid. This number, called fpd, is given as a positive number, meaning that this is the amount of temperature that the salts in a given solution has lowered the freezing point from 0 degrees Centigrade, which is the freezing point of pure water.
Hence, the fpd of sea water, with a salinity of 34.7 o/oo is 1.91, which tells us that sea water freezes at -1.91 degrees Centigrade.
Likewise, the fpd of human blood is 0.56, or human blood will freeze at -0.56 degrees Centigrade.
This tells us that the higher the salinity of a fluid, the higher its fpd, or the lower temperature at which that liquid freezes, when making comparisons between 2 liquids of different salinities.
The chemistry of sea water has implications to organisms that live in the oceans.
1. Evolution of plants and animals.
Since all of the elements that make up the biological organism are present in sea water, it is most probable that both plants and animals (and probably the most primitive forms of life, the precursors to plants) evolved in the oceans.
2. Most organisms are constantly "battling" to maintain the level of water and salts in their bodies within whatever narrow limits of tolerance.
3. This maintenance of a suitable salt/water balance expends considerable amounts of energy, whether in using special mechanisms or in the manufacture of a covering that prevents water and salts from entering or leaving the body.
Chemistry considerations for plants, in general.
1. Most of the living space in the oceans available to plants are shallow (upper 50-80 meters) since light is of primary concern to plants. Thus, the marine plants have "gone in the direction" of becoming "floating plants," called phytoplankton.
2. However, all plants do need a number of constituents in sea water.
a. Physical conditions, such as proper temperature, right light quantity and quality, suitable pH range, suitable substrate (for attached plants), and suitable salinity range.
b. Macronutrients, such as carbon, hydrogen, oxygen, magnesium, potassium, phosphorus, and nitrogen, that are found in good concentration and required by all plants.
c. Micronutrients, such as iron, calcium, zinc, manganese, and copper, essential in the construction and action of enzymes, only necessary in minute quantities.
3. Certain elements needed only by certain plants: silicon for diatoms for their shells, sodium for blue-green algae, and molybdenum for many others.
4. Accessory growth factors, such as vitamin B12.
5. The critical determinants for plant productivity in the oceans are phosphorus, nitrogen, and iron (sounds familiar? these are also required by plants for good production on land!).
The composition of sea water and the body fluids of many animals are alike. This makes this saline environment the most appropriate for living cells, containing all the elements essential for the growth and maintenance of protoplasm.
Which brings us to the question of the composition of sea water!
In the open ocean, sea water has an average salinity (saltiness) of around 35 (34.7) o/oo (parts per thousand), which is the same as 3.5 %. In oceanography, the salinities are measured in o/oo, or simply by moving the decimal point one space to the right to change % to o/oo. The salinity is simply the content of the dissolved salts in water, or the measured amount of solids dissolved (in grams) in a given amount of water (one kilogram)--this gram per 1000 grams makes salinity be given in parts per thousand.
Since the proportions of the major chemical constituents of sea water is remarkably uniform in most parts of the open ocean, measuring only one of the major components can determine the salinity by calculation. Chemical/physical oceanographers used to measure salinity by determining the concentration of chloride by chemical means. However, today, salinities are more rapidly and easily measured by determining the electrical conductivity of sea water with a device called a salinometer.
The major constitutents of sea water are sodium and chloride (hence, salt water is usually given chemically as NaCl, which are the symbols for sodium/Na and chlorine/Cl). However, sea water, as given earlier as water being the "universal solvent," contains many, many other elements. Other significant components include sulfates (SO4), Magnesium (Mg), Calcium (Ca), Potassium (K), and bicarbonates (HCO3). The ratios of these salts to one another do not vary much in the oceans or over time periods. Those salts and elements that do not vary much over time in an area are called "conservative elements"--these are sodium, magnesium, calcium, potassium, chlorine, sulfate, carbonate, bicarbonate, bromine, boric acid, lithium, rubidium, barium, aluminum, uranium, lead--in fact, more than 99.9% of all the dissolved salts.
On the other hand, some minor constituents show marked variation in relative concentrations over time, due to their selective removal from the water by living organisms. These are called "non-conservative" elements--phosphate, nitrate, and silicon. These 3 elements/compounds tend to be in short supply in surface waters where they are taken up by plants, but their concentrations increase sharply below the depths of photosynthesis as a result of their release into the water from the decomposition of sinking organic particles.
The ratio of major salts to each other, and usually in total concentrations as well, are similar in sea water and in the body fluids, especially of the marine invertebrates (those animals without a vertebral column. But this similarity is not restricted to just the marine invertebrates but extend out, more or less, to include "higher" (and presumably more complex) animals/vertebrates, such as fish, amphibians, and mammals.
There are some variations noted to this general similarity, but they are local in sites, affected by climate or the weather. One particular location in the oceans where one can expect and do observe considerable variation is the edge of the oceans, which most of us explore as the tide pools.
To date, the major areas of concern with the chemical content of the oceans have been in the shallow seas (less than 200 meters of depth), but since these are the areas of heaviest biological productivity or human contact/significance, the concerns voiced have not been insignificant. In the Pacific Ocean, many of the coral reefs in the central and southwestern Pacific are relatively "clean," but the northwestern line from the Philippines to Japan are critical due to overexploitation and pollution. Some of the coral reefs associated with the South Pacific islands that compose Melanesia, Micronesia, and Polynesia, are, at best, threatened and bear corrective measures.
Many of us are very much interested and/or involved in the oceans, whether that be the Pacific, Atlantic, or the Indian
Ocean.
This is the start of a series about the oceans, its many, many plants and animals, and topics of interest to us in research and as good consumers of these most important resources. We will wend our way through the oceans as the physical, chemical, and geological environment, the biota that live in them, and topics of special interest, such as coral reefs, tidepools, fishing, scuba, snorkeling, boating, surfing, and many of the other activities that revolve around the oceans.
Throughout this series, the reader will have the exposure to a marine resource/marine biology course, all without a single examination but one that is chock full of information and suggestions. Every effort will be made so that all, even for those without too much of a science background, will be able to comprehend the discussions. Enjoy!
Water as an environment about which we enjoy.
There are certain physical properties of water as an environment, especially as related to organisms that live in this "magic to life." We always describe water as being wet, meaning that it does prevent the loss of internal water as a result of dessication. The fact
that water has a high heat capacity (highest of all solids and liquids except for liquid ammonia) means that it prevents the extreme ranges in temperatures so that the tendency is for the maintenance of uniform body temperatures to those aquatic organisms. However, the heat transfer by water movements is large, which translates to the fact that we are cooler (actually, we get cooler faster) in water than in air (it is said that this transfer of heat is more than 25 times faster than in air).
Water, due to its high viscosity (the internal fluid resistance, caused by molecular attraction, which makes it resist a tendency to flow), while offering high resistance to a body/organism moving through it, does support that body well. This allows us, as swimmers, to "float" better in water than we do in air. Thus, organisms in the aquatic environment spends considerably less energy to counteract the force of gravity (tendency to sink) but yet expend more energy in moving through the water. Just take a look at how we can do somersaults, stand on our hands, back flips, or just hang suspended in water while many of us could do none of these in the air which is our normal, every day environment. But, the world record for running is less than 10 seconds per 100 meters while taking more than 48 seconds for moving that same distance in water.
Water is a relatively imcompressible (cannot be squeezed) substance, so that the pressure in water increases strictly as a result of the weight of the water through depth. Water increases in pressure with depth at the fairly constant rate of 14.7 pounds per square inch (psi--this number is set as 1 Atm of pressure) per 10 meters of depth. In other words, the weight of a 10 meter-column of water that is above a square inch of surface in the water is approximately 15 pounds) Air, on the other hand, is a easily compressed substance, so that, higher pressures of air are encountered as one gets closer and closer to the surface of the earth. The compressibility of air leads to areas of high/low pressures, with the associated good/bad weather encountered. The constant rate of change of pressure of water allows many organisms to exist at great depths without negative consequences; this is especially significant to those organisms that have any air spaces within their bodies (such as marine mammals, like scuba divers).
Note: for snorkel/scuba divers, there are 2 significant air spaces that are "part of the body" as they wend their way to depth. Such air spaces do get squeezed at depth, so that according to the laws of physics, as the pressure increases, the volume decreases proportionally (if the water pressure doubles, as it does when one goes from the surface to 10 meters of depth, in that the pressure goes from 1 Atm at the surface to 2 Atm, the volume of any air space decreases from 1 unit volume to 1/2 unit volume). The first of these is the lung system, which is a compressible system. The effect of increased pressure "squeezes" the lungs, but the human lung system has evolved so that there is a minimum lung volume that is always present, below which there is mechanical damage to the lungs. This is the so-called "thoracic squeeze" suffered by breath-hold divers; we will discuss this further in the section dealing with marine mammals. The other "body part" that is taken below the surface by divers is the face mask, which is an air-filled space that has no connection to the body other than through the nose. Thus, as the pressure increases, one needs to exhale a little air into the face mask through the nasal passages in order to
"equalize" the pressure so that it is the same as the external water pressure. If one fails to do this, the reduction in air volume will make any "soft tissues" attempt to make up that decreased volume (for the most part, the only soft parts in the face mask are the eyes). This results in the vivid, striking, red-instead-of-white parts to the eye, or an "eye squeeze."
The dissolving power of water is greater than that of any other liquid, which means that there are more different substances dissolved in water and in greater concentrations; this most efficient solvent contains all the essential elements necessary for life. Scientists refer to Earth as the Water Planet, and the search for traces of water in other heavenly bodies is essentially the clue as to the potential for life on those heavenly bodies. The suggestion of water (past or current) on Mars makes it very intriguing that perhaps there has been or is some form of life as we know it on that planet.
The transparency of light through water is relatively great, and thus, plant life, which depend on light, can live relatively deeper than it could were the Earth covered by any other liquid. A broad band of more than 50/80 meters of water over the surface of the oceans has sufficient light to support the growth of plants, and the subsequent growth of animals that do depend ultimately on the presence of plants.
Sea Water properties.
Sea water has physical characteristics a bit different than those of pure water which enables/allows organisms to live within the seas without the development of some highly specialized integuments/skin and regulatory systems for protection against sudden and intense environmental changes. On the other hand, this "protection" sometimes leads to significant influences on them with the influx of relatively small changes in the sea water surroundings.
Sea water is said to be a buffered solution. This simply means that, in chemical terms, changes in pH (acid to alkaline or vice versa) are resisted. This buffering property is due to several factors: the presence of fine clay particles in suspension in sea water; the interaction between carbon dioxide, carbonic acid, bicarbonate/carbonate ions, and boric acid. The pH of sea water is generally between 7.4 and 8.4 (from basic chemistry, we learned that a neutral pH, neither acid nor alkaline, is 7.0), which tells us that it is slightly alkaline/basic. Chemically,
this means that there can be an abundant supply of carbon (in the form of carbon dioxide) available for photosynthesis (production of organic matter by plants through the energy derived from sunlight) without any undue influence on the presence of marine animals that may be sensitive to small changes in pH. This allows for the growth of embryos and species that have not developed complex regulatory mechanisms (as is true for many invertebrate groups). In the slightly alkaline conditions of the oceans, the many organisms that construct shells of calcium carbonate or other calcium salts can carry on this function much more efficiently than it could were the oceans acidic (which would erode any structure made of calcium carbonate).
The specific gravity (the weight per unit volume) of sea water is greater than that of fresh water, which offers more physical support to a body immersed in it. Sea water weighs more than fresh water (about 64+ pounds per cubic foot versus 62 pounds per cubic foot), and according to Archimedes' Principle, which tells us that the force exerted on a body immersed in a liquid is equal to the weight of the liquid that is displaced by that body, the buoyancy force on a person in sea water is greater than that experienced by that person in fresh water. This rarely comes into play at one given time, since we are always either in fresh water (in the swimming pool) or in the ocean; however, for the scuba diver going through training (where the initial water work is done generally in a fresh water swimming pool or environment and then subsequent water work is done in the oceans), donning a wet suit (which offers positive buoyancy which needs to be counteracted in order for the diver to descend to the bottom), the weight equivalent to enable a descent is configured initially for the fresh water environment. Then, in the transfer to the ocean, the diver has to put on more weight in order to achieve the same degree of "sinking" or counteraction for the positive buoyancy of the wet suit. Many of us have felt this, in the sense that it is so much easier to dive to the bottom of a fresh water pool than it is to get to a similar depth in the oceans.
Marine animals and plants, are, for the most part, practically the same weight/specific gravity as the sea water in which they live. Since the animals and plants on land are much heavier than the air, they have evolved complex systems to counteract the force of gravity. Marine organisms do not need to expend as much energy to overcome the force of gravity, and the physical support offered by sea water obviates/makes unnecessary the need for elaborate skeletal structures, which explains the numerous jellyfish, unarmored mollusks/snails, dinoflagellates (plants), and large marine mammals. The hard shells of many plants and animals have been developed mainly for burrowing and digging, protection, and the framework for the attachment of muscles used for digging, creeping, or swimming.
However, just as with fresh water, the increased viscosity of sea water offers more resistance to an object moving through it.
Next chapter: relationship between the composition of sea water and the body fluids of organisms.
