WATER THE CRADDLE OF LIFE 1. Water covers about ¾ of the earth s surface. 2. In living organisms water comprises about 70-95% by weight. a. Human body is about 60% in young adult males and 50% in young adult females (ranges from 45 to 75%) 1) plasma about 93% 2) adipose tissue about 10% 3) bone about 20% 4) What is the reason for the sexual difference? b. Jellyfish can be about 99% water. c. Seeds and spores can be as little as 5% d. Most cells are 80-90% water. 3. Most organisms depend on a continuous turn over of water; therefore, the body attempts to balance the input of water with the output. 4. Hydrogen bonding is responsible for most of water s special properties. a. Water molecule (fig. p. 26) + + H H O - - Figure 1. Showing the polar nature of the water molecule b. Each water molecule can bond to a maximum of 4 other charged molecules. (fig. 2.16, p. 27) c. Electronegativity 1) Both hydrogen and oxygen attract electrons and thus have electronegativity. 2) But oxygen atom is more electronegative and thus attracts the shared electrons more strongly than the hydrogen atoms do. 3) Therefore the shared electrons are closer to the oxygen nucleus than the hydrogen nucleus giving the oxygen atom a partial negative charge. This is represented by the Greek letter delta ( - ) and signifies a partial charge which is much weaker than the charge on an ion. 4) Hydrogen has the shared electrons less in the vicinity of its nucleus and thus
bears a partial positive charge ( + ). 5) This results in a molecule with opposite charges at the two ends, polar molecule. 6) Polar molecules attract one another by the + charge of the one to the - charge of the other. 5. Cohesive force. a. The attraction of water molecules for each other is called cohesion. b. Surface Tension (demonstration) (fig. 2.17,p. 28) c. Placing a material that is soluble in water lessens the attraction of the water molecules. (demonstration) d. Causes water to assume smallest area--rounds up into drops. (demonstration) 6. Adhesive force. a. Attraction between unlike molecules. b. Water rising in a capillary tube. (demonstration) 1) The water adheres to the glass and is pulled upward against gravity. 2) The water sags in the center due to pull of gravity causing the meniscus. 7. High specific heat. a. Specific heat is the amount of heat that must be absorbed or lost in order to bring about a change of 1 C in one gram of the substance. b. Takes 1 small calorie to change the temperature of 1 gram of water 1 C. c. This is the reason that water is a good temperature buffer. d. Due to hydrogen bonding 1) Heat must be absorbed to break bonds 2) Heat is released when bonds form. 3) The stronger the hydrogen bonding the higher the Specific Heat. 8. High heat of vaporization (evaporation) a. Takes 540 calories to change 1 gram of water at 100 C to water vapor. b. Much of the heat of the sun that reaches the earth is used to evaporate seawater. c. Heat is released as vapor condenses to form rain.
d. Sweating regulates body temperature. 9. Liquid to solid (water to ice) a. Water become most dense to 4 C b. At 0C molecules become locked in a crystalline lattice (fig.2.16, p. 27). This keeps molecules at a distance. c. Ice less dense than water; therefore, it floats on water. d. 10% fewer water molecules in a solid state than in a liquid state for the same volume. 10. Water is a powerful solvent. a. Many substances dissolve in water. b. Polar molecules and ions are soluble in water. c. Water molecules gather around any particle that bears an electrical charge. d. Non-polar molecules don t dissolve in water. e. A solution is made up of a solvent (water in living organisms) and a solute. f. Demonstration of salt in water (fig. 2.14, p. 25) 450 ml water 10 ml salt Total number of ml = g. Hydrophilic (water loving) Hydrophobic (water fearing) 1) Cell membrane 2) Polar exterior (tissue fluid) and interior (cytoplasm) 3) Bilipid inside is non-polar 11. Acids and Bases a. Pure water at 25 C dissociates into + H 3 O + OH - with each at a conc. of 10-7 b. This is indicated as a ph of 7 1) ph is the negative log of the hydrogen ion conc. 2) This changes the -7 to a +7 c. The product of the hydrogen conc. X the hydroxyl conc. = 10-14 d. If H + conc. is 0.1 gram in a liter of pure water, this can be written as 10-1 or ph 1
e. If H + conc. is 0.001 gram in a liter of pure water, this can be written as 10-3 or ph 3 f. If the H + conc. = 10-3, than the OH - conc. = 10-11. g. ph scale is 0----------14 (fig. 2.18,p. 30) 1) ph of 7 is neutral, the H ion conc. = the OH conc. 2) Below ph of 7 it is acid and the H ion conc. is greater than the OH ion conc.. 3). Higher than 7 it is alkaline and the conc. of H ions is lower than the OH - conc.. DISCUSSION QUESTIONS OVER WATER THE CRADLE OF LIFE 1. Bone is a much more solid tissue than adipose tissue yet it contains a higher percent of water than adipose tissue. Explain. 2. Explain the reason that one water molecule can bond with four other water molecules. 3. One commercial cleaning solution claims that it makes water wetter. Assuming that this is correct, explain it. 4. What is meant by the statement Water is a good temperature buffer? Explain. 5. Explain the reason that the heat of vaporization is so relatively high in water. 6. Explain the reason that ice, a solid, is lighter than water and thus floats on water. 7. Compare ethyl alcohol and corn oil in their relationship to water using the terms hydrophilic and hydrophobic.
8. What does the abbreviation ph stand for? 9. List three acids that you commonly eat. 10. What is the reason that the adult female body is only about 50% water and the young male s body about 60% water. CRITICAL THINKING QUESTIONS. 1. There is a line in the poem The Rhyme of The Ancient Mariner that goes Water, water everywhere and not a drop to drink. On a biological (physiological) basis explain the justification for that statement. 2. An astronaut was asked the question If there are 20 drops to a milliliter of water, as it drops from a pipette on earth, how many drops would there be on the moon. To make it easier for you, you just have to decide did the astronaut answer (A) more (B) less (C) same number. Explain your answer. OBJECTIVE QUESTIONS 1. (A) Human body cells (B) Human sperm cells (C) Jelly fish (D) Plant spores contain the less percent water. 2. A polar molecule has a charge on (A) one (B) two end(s). 3. The meniscus found at the upper level of the water in a tube shows us that the cohesive force of water is (A) greater (B) lesser (C) about the same as/than the pull of gravity. 4. In the case of water rising in a glass tube, what shows (A) adhesive force (B) cohesive force (C) both A and B (D) neither A or B. 5. Each water molecule can form hydrogen bond(s) with a maximum of (A) 1 (B) 2 (C) 4 (D) 4 (E) 8 water molecule(s). 6. Starting with a liter of water at 10 degrees centigrade, it would take (A) 90 (B) 100 (C) 212 (D) 540 (E) 630 calories to heat it to 100 degrees centigrade but still be water. 7. Water is most dense at (A) 100 (B) 32 (C) 4 (D) 0 degrees centigrade. 8. Pure water has (A) hydrogen (B) hydroxyl (C) both A and B (D) neither A or B at an ionic concentration of 1 x 10-7. 9. A ph of 12 means the solution is (A) acidic (B) basic (C) neutral. 10. (A) Surface tension (B) High specific heat (C) High heat of evaporation (D) Two of the preceding (E) All the preceding is/are the result of hydrogen bonding of water molecules.