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CHAPTER 3 Water and the Fitness of the Environment

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1 CHAPTER 3 Water and the Fitness of the Environment

2 PROPERTIES OF WATER The most common substance on Earth.
The basis of life. It exists in all three forms of matter: solid, liquid, and gas. Human beings are made up of 70% water. The brain is made up of 70% water and the lungs are about 90%. The bloods is made up of 83% water, which aids in digestion, chemical waste transportation, and controlling body temperatures. Cells are 70-95% water and water also helps move nutrients and other substances into and out of the cells. Life on Earth is possible because of water. Before there was terrestrial life, there was life in the oceans (microorganisms).

3 WATER Water is made up of hydrogen bonds, which are the weakest of the polar covalent bonds. Oxygen is more electronegative than hydrogen, so the electrons in the bond spend more time closer to the oxygen atom. This is wy water has that mickey mouse head shape. Water is a polar molecule. It has partial positive and partial negative poles.

4 PROPERTIES OF WATER It has a high heat capacity = can absorb large amounts of heat. It is less dense in the solid form (ice) than in the liquid form, due to ice crystals. Water has a pH of 7 (neutral). Cohesion Adhesion Water molecules stay close to each other as a result of hydrogen bonding. Bonds are forming, breaking, re-forming constantly. This is why water is bonded to its neighbors most of the time = Cohesion. Cohesions contributes to capillary action. As water evaporates from the leaves, water molecules tug on the molecules farther down creating an upward pull. This is how plants intake water from the roots. Adhesion of water to other substances, like the plant cells, helps counter the pull of gravity in capillary action.

5 COHESION Cohesion = an attraction between substances of the same kind.
Surface Tension of Water Due to Hydrogen bonding Adhesion = an attraction between different substances. Capillary Action in plants

6 SURFACE TENSION It is a measure of the strength of water’s surface.
Water is “sticky” and “elastic.” It clumps together. It has a skin. It has a HIGH surface tension. Water and wax paper. Water striders. Between water and air there is an ordered arrangement of water molecules bonding together with the ones next to each other and with the ones underneath the surface. This makes water appear to be coated with an invisible film or skin.


8 CAPILLARY ACTION Process by which water moves up through the roots of plants. It is possible because of adhesion and cohesion.

9 GREEN BASILISK LIZARD “Jesus Christ Lizard”


Heat vs. Temperature Water has a high specific heat = 1 cal/g/oC High heat of evaporation. Evaporative cooling Sweating What happens when it is “hot and humid” outside? Water absorbs heat from warmer air and release heat to cooler air. Only little variation in its own temperature. Kinetic energy = energy of motion Heat = measure of the total amount of kinetic energy due to molecular motion. Temperature = measures the intensity of heat due to the average kinetic energy of the molecules. Cal = amount of heat needed to raise temp. of 1g of water by 1oC. Specific heat = amount of heat that must be absorbed or lost for 1g of that substance to change its temperature by 1oC. Because of high specific heat water temperatures fluctuate less when absorbing or loosing heat. Heat has to be absorbed to break hydrogen bonds. Heat is released when hydrogen bonds form. Relevance? Oceans can maintain a fairly constant temperature regardless of its surroundings. Water is cool during the day and warmer at night. Heat of vaporization = amount of heat that a liquid must absorb for 1g to be converted to gas. Evaporative cooling = as liquid evaporates, the surface of the liquid that remains cools down. It prevents organisms from overheating by moderating temperature. (Humidity discomfort = sweat evaporates less)

12 WATER’S EXPANSION Less dense as a solid than a liquid.
Due to hydrogen bonding: Not enough kinetic energy to break hydrogen bonds Crystal lattice structure = each water molecules bonded to 4 other. Ice floats = crystal structure has “holes” and takes up space Ice has less molecules than the same volume of liquid water. Less dense Floating ice protects water below from cooler air = insulating blanket.

13 THE SOLVENT OF LIFE Solution = A homogeneous mixture of two or more substances . Solvent Solute Aqueous solution Ionic compounds and polar molecules dissolve well in water. Non-polar molecules do NOT dissolve well in water. OIL and Water Hydrophilic & Hydrophobic Colloid Solvent = the dissolvent agent of a solution. (I.e. water) Solute = the substance that is dissolved. Hydrophilic = (Greek hydro = water; philios = loving) Has an affinity for water. Hydrophobic = (Greek phobos = fearing) repels water Detergent = Has a hydrophilic end and a hydrophobic one. Colloid = a mixture made up of a liquid and particles that (because of their large size) remain suspended in the liquid. Ex. Cellulose (paper towel; cotton; plant cells)











24 ACIDS AND BASES Acids = Compounds that form hydrogen ions (H+) when dissolved in water. Bases = Compounds that reduce the amount of hydrogen ions (H+) in a solution. pH scale = based on the concentration of hydrogen ions in a solution.

25 WATER STRIDER Look at the water strider in the pictures and answer the following question: Imagine you are the first human being to discover this creature. How would you explain to the scientific community how this insect is able to “walk” on water?

26 QUESTIONS Many mammals control their body temperature by sweating. Which property of water is most directly responsible for the ability to sweat to lower body temperature? A. The release of heat by the formation of hydrogen bonds. B. The absorption of heat by the breaking of hydrogen bonds. C. Water’s high surface tension.

27 QUESTIONS How does electronegativity affect interactions between water molecules? Can water molecules bond like this? Explain. H H O O H H

28 QUESTIONS The bonds that are broken when water vaporizes are:
A. ionic bonds B. polar covalent bonds. C. nonpolar covalent bonds.

29 QUESTIONS Which of the following is an example of a hydrophobic material? A. Paper B. Table salt C. Wax D. Sugar E. Pasta

30 “The heat doesn’t bother me; it’s the HUMIDITY that does!”
QUESTIONS Describe how the properties of water aid in capillary action? Explain the phrase: “The heat doesn’t bother me; it’s the HUMIDITY that does!”

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