august 29, 2005 biology 107 water. water student objectives:as a result of this lecture and the...
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WaterWaterStudent Objectives:Student Objectives: As a result of this lecture and the assigned As a result of this lecture and the assigned
reading, you should understand the following:reading, you should understand the following:
1.1. For all living organisms, life depends upon water, and living things are For all living organisms, life depends upon water, and living things are made up mostly of water molecules (Hmade up mostly of water molecules (H22O)O)
2.2. The dipoles produced by the polar covalent chemical bonds between the The dipoles produced by the polar covalent chemical bonds between the hydrogens and oxygen of the water molecule allow for hydrogen bonding hydrogens and oxygen of the water molecule allow for hydrogen bonding between water molecules, and the properties of water are related to these between water molecules, and the properties of water are related to these intermolecular bonds.intermolecular bonds.
Water molecules "stick" to each other,Water molecules "stick" to each other, cohesion cohesion, and to , and to charged charged substances, substances, adhesionadhesion. The cohesive and adhesive . The cohesive and adhesive properties of properties of water allow it to rise against the force of gravity water allow it to rise against the force of gravity through capillarity.through capillarity.
WaterWater
Related to cohesion is the property of surface tension - a Related to cohesion is the property of surface tension - a measure of how difficult it is to stretch or break the surface measure of how difficult it is to stretch or break the surface
of a of a liquid.liquid.
Water’s hydrogen bonds moderate temperature and Water’s hydrogen bonds moderate temperature and decrease decrease water evaporation and vaporization.water evaporation and vaporization.
Ice is less dense than liquid water.Ice is less dense than liquid water.
Water's versatility as a solvent results from the polarity of its Water's versatility as a solvent results from the polarity of its molecules; substances that dissolve in water are called molecules; substances that dissolve in water are called
hydrophilichydrophilic (i.e., water-liking), while those that do not dissolve (i.e., water-liking), while those that do not dissolve in in water are water are hydrophobichydrophobic (i.e., water-hating). (i.e., water-hating).
Water3.3. A certain proportion of the water molecules dissociate into ions A certain proportion of the water molecules dissociate into ions
because of their polarity. The two ions formed in the chemical because of their polarity. The two ions formed in the chemical reaction that dissociates water are the hydrogen cation (Hreaction that dissociates water are the hydrogen cation (H++), which ), which is simply a proton, and the hydroxide anion (OHis simply a proton, and the hydroxide anion (OH--))
4.4. Some substances when dissolved in water dissociate and release Some substances when dissolved in water dissociate and release HH++ ions. By definition, these substances that release H ions. By definition, these substances that release H++ ions when ions when dissolved in water are called dissolved in water are called acidsacids. Acids increase the H. Acids increase the H++ concentration of the solution. That is, concentration of the solution. That is, the more acidic a solution, the the more acidic a solution, the higher its concentration of Hhigher its concentration of H+ + ions, and the lower its ions, and the lower its pHpH. .
5.5. A A basebase is any substance that accepts H is any substance that accepts H++ ions when dissolved in ions when dissolved in water.water.
Inventory of Water at the Earth's Inventory of Water at the Earth's Surface.Surface.
Reservoir Volume (cubic km x 1,000,000) Percent of Total
Oceans 1370 97.25
Ice Caps and Glaciers 29 2.05
Groundwater 9.5 0.68
Lakes 0.125 0.01
Soil Moisture 0.065 0.005
Atmosphere 0.013 0.001
Streams and Rivers 0.0017 0.0001
Biosphere (Animals & Plants) 0.0006 0.00004
Cohesion and AdhesionCohesion and Adhesion
Cohesion and adhesion of Cohesion and adhesion of water produces: 1) surface water produces: 1) surface tension and 2) capillary action.tension and 2) capillary action.
Mechanism by which plants Mechanism by which plants draw water upward from roots draw water upward from roots to leaves through small to leaves through small vessels. Mechanism by which vessels. Mechanism by which water moves through water moves through groundwater reservoirs groundwater reservoirs between the particles of rock.between the particles of rock.
Water Movement in PlantsWater Movement in Plants
Cucumber stem in cross Cucumber stem in cross section showing vascular section showing vascular bundles that convey water bundles that convey water by capillary action.by capillary action.
Hydrogen Bonding Helps Water Move Hydrogen Bonding Helps Water Move Through PlantsThrough Plants
Some trees can move water from their roots to their leaves at a rate of 25 mm (1 inch) per second.
Hydrogen Bonding Holds Waters Molecules Hydrogen Bonding Holds Waters Molecules Together and Produces Surface TensionTogether and Produces Surface Tension
High tea in spaceHigh tea in space
High Heat Holding CapacityHigh Heat Holding Capacity1.1. Water has a high boiling point, so water is a liquid over a wide Water has a high boiling point, so water is a liquid over a wide
temperature range.temperature range.2.2. Water has the ability to absorb much heat, so large bodies of Water has the ability to absorb much heat, so large bodies of
water can minimize temperature changes.water can minimize temperature changes.3.3. Water produces evaporative cooling. The heat loss Water produces evaporative cooling. The heat loss
associated with evaporation makes evaporation an effective associated with evaporation makes evaporation an effective way for organisms to shed excess heat.way for organisms to shed excess heat.
Hydrogen Bonding of Water Molecules to Other Hydrogen Bonding of Water Molecules to Other MoleculesMolecules
Ionization of WaterIonization of Water
In pure water only 10In pure water only 10-7-7 moles/liter of water are in dissociated, ionized form moles/liter of water are in dissociated, ionized form
pH ScalepH Scale
pH measures the hydrogen ion pH measures the hydrogen ion concentration of a solutionconcentration of a solution
The higher the HThe higher the H+ + concentration the concentration the lower the pH numberlower the pH number
AcidsAcids donate H donate H+ + , while , while basesbases accept accept HH+ +