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18.6: Fresh Water

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    Discussion Questions

    • Is water the source of life, why?
    • What is life?
    • Is life a symbiotic system of many lives?
    • What properties of water make water the prime ingredient of life?
    • What are the essential substances of life?
    • Other than material, what else is essential for life?
    • What is the role of water in supporting life?
    • Is there a life form involving no water?
    • Is there a method to determine the total water content?

    Not finished yet, but the major ideas are here now!

    Water Biology

    waterlily.jpgChemical and physical properties of water discussed in other pages are essential considerations for water biology. Natural water also contains biological matters as well as living creatures. In the discusssion of biology and water, you must feel pleasant, because they make each other grow more lovely as this picture from water lily cottage. The water pages of National Wildlife Federation, offers some interesting reading too.

    All living things have a cycle of life. A cycle involves all or some of these process: birth, growth, mature, reproduction, matamorphosis, and death. There are millions of living organisms on Earth, ranging from single-cell amebas, bacteria, to the complicated homosapiens. There are also viruses which are fragment of DNA or RNA that depend on host cells for their reproduction. They are not cells.

    Living things usually have cells that isolate their systems so that the cells contain unique materials to sustain the lives of cells. Cells regulate their contents (homeostatic), and carry out their metabolsims. They divide or making copies of themselves. Many reproduction process involve two individuals and future populations are subject to a greater diversity. Mutation is a fact of life, and many adopt to their changing environment.

    How life started? Let the research and debate continue by not giving any clusive statements here. A physical geography course suggests that the marine invertebrates began their life 600 million years ago, and they are followed by fish, land plants, amphibians, reptiles, mommals, and then flowering plants, in this order. All these started more than a hundred million years ago, and hominid (primate) line began its evolution 20 to 15 million years ago.

    There are strong evidences that life on earth appeared in a body of water. Only the planet Earth has three states of water, and it offers a suitable environment for life to began, among all nine solar planets. Since all life forms involve water. Water is seen as the source, matrix, and mother of life. Water is important, because water is required for life, and some people even consider water as life blood.

    Since water supports life, living organisms also modify their environment, changing the nature of the water in which they live. Biology of water pollution, lists the syllabus on a course including a laboratory section. Water and biology interweave into an entangled maze waiting for explorers and curious minds.

    Water dissolves or emulsifies other life-supporting substances and transport them to intercellular and intracellular fluids. It is also a medium in which reactions take place. Reactions provide energy (non-matter) for living. Energy causes changes, and manifestation of changes is at least related to, if not the whole, life. An organized and systematized set of reactions is essential in each life.

    Balancing Water in Bio-systems

    Many living organisms live their lives entirely in water as shown here in this photo from a job center talking about work in marine biology. Aquatic living organisms extract neutrients from water, yet maintaining a balance of electrolyte and nurrishment concentration in their cells. For living things not living in water, they extract water from their environment by whatever mechanism they can. Cells in their body are surrounded by body fluid, and all cells maintain constant concentrations of electrolytes, neutrints, and metabolites. The process of maintaining constant concentrations is called homeostasis. Certainly, some active transport mechanisms are involved in this balance.

    The rooting of every type of plants is unique. Generally speaking, plants having extensive roots are able to extract water under harsh conditions. On the other hand, some plants such as cactus, jade and juniper have little roots, but their leaves have a layer of wax that prevents water from evaporation. Water conserving plants tolerate draught, and they survive under harsh conditions. The picture shown here is a jade plant from the above link.

    Lately, some pumpkin growers harvested squash weighing almost 500 kg. At the peak of the growing season, the squash grows almost 0.5 kg a day. That is equivalent to 25 moles of water collected by the roots, discounting the water evaporated through the leaves. The growth is particularly good during a hot and wet day, but during a hot sunny after noon, the temperature of the leaves and fruits get very hot.

    Essential Electrolytes for Life Support

    In addition to water, many inorganic substances or minerals are essential to life. These substances ionize in water to form ions and their solutions conduct electricity. Therefore, they are called electrolytes. Because most of these substances are already dissoved in natural water, we list ions instead of the mineral they come from.

    When ions dissove, they form complexes with water molecules. For most metals, the first sphere of coordination usually involve 6 water molecules. For example, when sodium chloride dissolve, we have

    \[\ce{NaCl + 12 H2O <=> Na(H2O)6+ + Cl(H2O)6^{-}}\]

    \[\ce{FeCl2 + 18 H2O <=> Fe(H2O)62+ + 2 Cl(H2O)6^{-}}\]

    Formation of complexes are due to the high dipole moment of water, and the dissolution can be attribute to the high dielectric constant (80). However, in most publications, we ignore the water molecules in the complexes, and simply consider them as ions.

    In the following, we describe some essential ions or salts as electrolytes.

    • Sodium chloride, Na+ and Cl-
      NaCl is readily dissolved and absorbed in extracellular fluid. The two ions help to balance water, acid/base, osmotic pressure, carbon dioxide transport, and excreted in human urine and sweat. Lack of sodium chloride shows symptoms of dehydration.
    • Potassium, K+
      Good sources of potassium ions are vegetables, fruits, grains, meat, milk, and legumes. It is readily absorbed, and actively transported into the intracellular fluid. Its function is similar to that of sodium ions, but cells prefer potassium ions over sodium. Lack of potassium leads to cardiac arrest.
    • Calcium, Ca2+
      Divalent calcium ions are usually poorly absorbed by human, but the are essential for the bones, teeth, blood clotting. Lack of calcium hinders growth and osteoporosis in old age.
    • Phosphates, PO43-
      Calcium phosphate is essential for bones, teeth, etc. However, phosphates are also responsible for many life reactions. ATP, NAD, FAD etc are metabolic intermediates, and they involve phosphate. Phospholipids and phosphoproteins are some other phosphate containing species.
    • Magnesium, Mg2+
      Magnesium ions are essential in chlorophyll. These ions are absorbed readily, and compete with calcium at times. Magnesium and calcium ions are present in hard water, and this link alerts the lack of magnesium leading to cardiovascular disease.
    • Ferrous or ferric ions, Fe2+ or Fe3+
      Usually known as iron, but iron are present either as divalent or as trivalent ions. Iron is absorbed according to body need; aided by HCl, ascorbic acid (vitamin C), and regulated by apoferritin. In mammals, iron is stored in liver as ferritin and hemosiderin. Iron deficiency leads to anemia. Good food sources of iron are liver, meats, egg yolk, green vegetables, and whole grains.
    • Zinc ions, Zn2+
      Zinc ions are important ingredients for many enzymes. They are present in insulin, carbonic anhydrase, carboxypeptidase, lactic dehydrogenase, alcohol dehydrogenase, alkaline phosphatase etc. Like iron, zinc deficiency leads to anemia and poor growth.
    • Copper ions, Cu2+
      Copper ions help iron utilization, and this metal is present in may enzymes.
    • Cobalt ions, Co2+
      Cobalt ions are centers of vitamin B12, and deficiency of which leads to anemia.
    • Iondine ions, I-
      Iondine is a constituent of thyroxin, which regulates cellular oxidation.
    • Fluoride ions, F-
      Fluoridation of drinking water is often a controversal issue. Childen's teeth are less seceptible to decay. Once they began to bruch their teeth, the fluoride in tooth paste is sufficient.

    The eletrolytes listed above are present in significant amount in water, or fluids of organisms. There are some metals present in very minute quantities in biological systems, and these are not listed above.

    Metal ions also interact with proteins. An enzyme is usually a very large protein molecule, and it folds into a kidney shape enclosing one or more metal ions forming a complex. The metal is usually responsible for the enzyme activity. Cobalt, copper, iron, molebdenium, nickel, and zinc have groups of enzymes each, and further discussion can be found in The Prosthetic groups and Metal Ions in Protein Active Sites Database (PROMISE). A general discussion is called bioinorganic chemistry and this site has an extensive General references on Bioinorganic Chemistry.

    Balancing Electrolytes

    Ions Extracellular Intracellular Interstitial
    Na+ 140 10 150
    K+ 5 150 4
    Ca2+ 10 4 6
    Mg2+ 6 80 4
    Total 161 244 164
    Cl- 103 2 120
    HCO3- 30 10 30
    HPO42- 4 177 4
    SO42- 2 10 2
    Organic acid 6 5 6
    Protein 16 40 2
    Total 161 244 164

    Electrolyte balance are maintained by passive transport or diffusion and slective active transport mechanisms. Diffusion process tends to make the concentration all the same throughout the entire fluid, but active or selective transport moves ions to special compartment. For example, the active transport of sodium and potasium by an enzyme called sodium-potassium ATPase is usually known as sodium-potassium pump. This process pumps potassium ions inside a cell while removing sodium ions from the cells. Thus, a high concentration of potassium is maintained inside cells. Energy is required in active transport, and cellular metabolism provides the energy and the necessary molecular motions to facilitate the process.

    Hormons are produced by special cells, and they are responsible for the communication between various part of the body. Some complicate harmon actions regulates the rate of transport and balance the ion concentrations depending on the portion of the tissue and the need. This is generally called the hormonal effects following the suggestion of human biochemistry.

    Gibbs-Donnan effect considers the equilibrium in compartments that are separated by memberances or cell walls. There will be no net change when the products of concentrations of say [Na+]1, [Cl-]1 are the same for compartments 1 and 2.

    [Na+]1 [Cl-]1 = [Na+]2 [Cl-]2

    the subscript 1 and 2 refer to the two compartments. When no other components are present, we have

    [Na+]1 = [Cl-]1 = [Na+]2 = [Cl-]2

    But if compartment 2 has a sodium salt with other anions, this salt ionize to give Na+ too. The above condition will not be maintained, in this case. In other words, thermodynamic will be a force to adjust the concentrations.

    In general, the cations should be balanced with anions. Otherwise, the solution will be charged.

    Water in Human Biology

    In human, water in the tissue and body fluid is mostly free, but some fraction may be bounded in pockets of hydrophilic compartments. Body fluids have many electrolytes and neutrients dissolve in them.

    Intracellular fluid 70%
    Interstitial fluid (lymph) 20%
    Blood plasma 7%
    Intestinal lumen etc. 3%

    Human Biochemistry by J.M. Orten and O.W. Neuhaus (1982), 10th Ed. suggests that about 70% of human body weight is water, most found in three major compartments: 70% intracellular fluid, 20% interstitial fluid, and 7% blood plasma, and only 3 % in intestinal lumen, cerebrospinal fluid and other compartments.

    However, Human Biochemistry also suggests that blood makes up about 8% of the total body weight.

    Example 1

    For a person weighing 50 kg (110 lb), what is the weight of the blood?

    From the distribution given above,

    Amount of blood = 50 kg * 0.08
    = 4 kg.

    This is a lot of blood, and donating 0.5 L of blood will not affect the normal function of the blood.

    Input Output
    Drinking 400 g Skin 500 g
    Beverage 580 Expired air 350
    Preformed water
    in solid food
    720 Urine 1100
    Metabolic water 320 Feces 150
    Total 2020 Total 2100
    Balance -80 g?

    Water in human comes from ingestion. Aside from drinking water, there is other beverages. Much of the food also contain water. When food is oxidized in the cells, all hydrogen in food converts to water, which is called metabolic water. Water is excreted via urine, feces, skin, and expiration. A typical daily water balance is shown in a table here. Water balance is maintained between cells and fluid, and the output depends on kidney functions and body insensible perspiration (Expired air from the lung is saturated with water vapor, and evaporation from the skin).

    Drinking Water

    Drinking water affects health. An Excite search using the phrase "drinking water" came up with 57890 documents. Drinking Water Resources gives annotated links to web sites that provide information about the drinking water.

    A rather recent book Chemistry of Water Treatment by S.D. Faust and O.M. Aly, 2nd Ed. (1998) [TD433 F38 1998] addresses the standards for drinking water in the first Chapter. The standards have changed over the years, as we better understand the science.

    Safe drinking water is a suitable combination of minerals and electrolytes. Usually, one should not drink water softened by water softeners. Using distilled water for beverages and cooking may not reach your set goals. Hard water with calcium and magnesium ions is good for drinking.

    Usually, a government set up a non-profit organization to provide rules for safe drinking water. This organization has an infrastructure to monitor drinking water systems, and it shall also carry out research to improve the quality of drinking water.

    Regarding making rules, reliable tests should be developed to determine the electrolyte we have mentioned, plus others such as lead ions, Pb2+, mercury Hg2+, methylmercury, arsenic, radioactivity, etc. Bacteria tests should be carried out regularly. This organization should also have a communication channel to release relavant message.

    The Environmental Protection Agency of the U.S. gives a list of comtaminants. The list has suggested limits, and it divides the contaminants into

    • Inorganic substnaces
    • Organic substances
    • Radioactivities (alpha and beta rays, radium)
    • Micro-organisms

    Among inorganic substances, limits are given to contents of antimony, arsenic, asbestos, barium, beryllum, cadmium, chromium, copper, mercury, nitrate, nitrite, selenium, and thallium.

    More than 50 organic compounds are on the list, and some familar ones are: acrylamide, benzene, carbon tetrachloride, chlorobenzene, 2 4 D, dichlorobenzen, dioxin, polychlorinated biphenyls (PCBs), toluene, and vinyl chloride. Many of these have a zero limit.

    In terms of microorganisms, Giardia lamblia, and Legionella, are checked. Furthermore, viruses, turbidity, total coliforms, and heterotrophic plate should be checked.

    Contaminant Standard
    Aluminum 0.05 to 0.2 mg/L
    Chloride 250 mg/L
    Color 15 (color units)
    Copper 1.0 mg/L
    Corrosivity noncorrosive
    Fluoride 2.0 mg/L
    Foaming Agents 0.5 mg/L
    Iron 0.3 mg/L
    Manganese 0.05 mg/L
    Odor 3 threshold odor number
    pH 6.5-8.5
    Silver 0.10 mg/L
    Sulfate 250 mg/L
    Total Dissolved Solids 500 mg/L
    Zinc 5 mg/L

    The secondary standard lists most electrolytes as shown in this table on the right.

    The Secondary Drinking Water Standards are non-enforceable guidelines regulating contaminants that may cause cosmetic effects (such as skin or tooth discoloration) or aesthetic effects (such as taste, odor, or color) in drinking water.

    There are many brands of bottled drinking water, they have been very popular only in recent years. Do we know the bottle procedure? Is the industry regulated? Is the water quality reliable? Are all bottled water the same? Is there a brand bottled water for real good health? Do we know what should be in healthy drinking water? There is an opinion expressed in Ontario Clean Water Agency (OCWA). Check it out.

    The magnesium web site gave the following news release Oct. 4, 1999. According to the U.S. National Academy of Sciences (1977) there have been more than 50 studies, in nine countries, that have indicated an inverse relationship between water hardness and mortality from cardiovascular disease. That is, people who drink water that is deficient in magnesium and calcium generally appear more susceptible to this disease. The U.S. National Academy of Sciences has estimated that a nation-wide initiative to add calcium and magnesium to soft water might reduce the annual cardiovascular death rate by 150,000 in the United States. This is a good summary from the report.

    Sports Drinks

    Sports talk gives information about Sports Drinks. This is science, art, testing, and myth. However, some fundamentals should be considered.

    Our bodies are mostly water, about 70%. The body fluid has many different things dissolved in it, particularly salt. the salinity - varies somewhat with where you take the sample of water to measure. Don't worry about that). I recall the concentration as being 0.5%, but I'm not sure. Doctors call this "normal saline".

    Now if you put a human, or other animal, cell in saltwater that is the same concentration as the saltwater inside the cell, the cell pretty much just sits there. If you put it in distilled water, the cell absorbs the water through its cell membrane - called diffusion - until it eventually pops. If you put the cell in concentrated saltwater, the cell looses water. The water diffuses out of the cell through the membrane, leaving a small, shriveled up cell.

    What does this have to do with sports drinks? If you give someone distilled water, it seems like they would absorb the water faster because of what I just described. On the other hand, during sweating, you're loosing sodium, potassium and small quantities of other electrolytes. If you're exercising particularly long or hard, you need to replace those electrolytes. Researchers found that adding some salt to water replaced the salt lost through sweating and helped the body to get water to the cells. If you look at a label on a Gatorade or other drink, you'll find that the main electrolyte is simple salt. But if you put too much of the electrolytes in the water, the cells shrivel up just like the way I described above.

    I hope that helps you understand what happens. This stuff on how cells swell up or shrivel up is in high school biology books, and maybe even in something you can find in your school's library.

    Taste and Order of Drinks

    Taste and order are sensations, and thus hard to quantify and systematize. Often, the Weber Fechner law is used. This law expresses the taste or order sensations S as being proportional to the logarithm of the stimulus R, with the proportional constant K,

    S = K log R

    For some common substances, the minimum amounts detected by expert nose or expert taster gives the sensation as a threshold, below which no taste or order was detected.

    However, orderous sensation of water may be reported as threshold order number (TON). If A mL of ordorous sample is diluted with B mL of order-free water to be "just detectable" to the expert nose, the TON is defined as

    A + B
    TON = -------------

    Similarly, a flavour threshold number (FTN) can be defined in the same manner.

    A + B
    FTN = -------------

    except that A and B are volumes of samples and taste free water used.

    These formulations show a method of defining some quantities that are, otherwise, very diffcult to quantify. There are other methods of reporting orders and taste, and some bottling companies have their standard methods of comparison.

    Of course, the source of order and taste comes are organic, inorganic compounds as well as bacteria, algae. For example, mercaptans such as C2H2SH and ammonia offers disagreeable smell and taste.

    Example 2

    A sample of water was tested by 10 expert noses, and only 5 of them can detect an order. Thus, this is "just detected". What is the TON for this sample?


    Since no dilution was used,

    TON = A / A = 1.


    If equal amount of orderless water is required to dilute it so that the order is "just detected", then the test order number is (1+1)/1 = 2.

    Contributors and Attributions

    18.6: Fresh Water is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by LibreTexts.