BIOL 1201 Chapter : Biology 1201 Ch 3
Biology 1201 Ch. 3
Polar covalent bonds in water molecules result in hydrogen bonding.
• A hydrogen bond forms when the slightly negatively charged oxygen of one
water molecule is attracted to the slightly positively charged hydrogen of a
nearby water molecule. Hydrogen bonding between water molecules is the
basis for water’s properties.
Four emergent properties of water contribute to Earth’s suitability for life.
• Hydrogen bonding keeps water molecules close to each other, and this
cohesion helps pull water upward in the microscopic water-conducting cells
of plants. Hydrogen bonding is also responsible for water’s surface tension.
• Water has a high specific heat. Heat is absorbed when hydrogen bonds
break and is released when hydrogen bonds form. This helps keep
temperatures relatively steady, within limits that permit life. Evaporative
cooling is based on water’s high heat of vaporization. The evaporative loss
of the most energetic water molecules cools a surface.
• Ice floats because it is less dense than liquid water. This allows life to exist
under the frozen surfaces of lakes and polar seas.
• Water is an unusually versatile solvent because its polar molecules are
attracted to charged and polar substances capable of forming hydrogen
bonds. Hydrophilic substances have an affinity for water; hydrophobic
substances do not. Molarity, the number of moles of solute per liter of
solution, is used as a measure of solute concentration in solutions. A mole is
a certain number of molecules of a substance. The mass of a mole of a
substance in grams is the same as the molecular mass in daltons.
• The emergent properties of water support life on Earth and may contribute
to the potential for life to have evolved on other planets.
Acidic and basic conditions affect living organisms.
• A water molecule can transfer an H+ to another water molecule to form H30+
(represented simply by H+) and OH-.
• The concentration of H+ is expressed as pH; pH=-log[H+]. Buffers in
biological fluids resist changes in pH. A buffer consists of an acid-base pair
that combines reversibly with hydrogen ions.
• The burning of fossil fuels increases the amount of C02 in the atmosphere.
Some C02 dissolved in the oceans, causing ocean acidification, which has
potentially grave consequences for coral reefs. The burning of fossil fuels also
releases oxides of sulfur and nitrogen, leading to acid precipitation.
Document Summary
Polar covalent bonds in water molecules result in hydrogen bonding. 3: hydrogen bonding keeps water molecules close to each other, and this cohesion helps pull water upward in the microscopic water-conducting cells, water has a high specific heat. Heat is absorbed when hydrogen bonds: a hydrogen bond forms when the slightly negatively charged oxygen of one water molecule is attracted to the slightly positively charged hydrogen of a nearby water molecule. Four emergent properties of water contribute to earth"s suitability for life. basis for water"s properties. of plants. Hydrogen bonding is also responsible for water"s surface tension. cooling is based on water"s high heat of vaporization. The evaporative loss break and is released when hydrogen bonds form. This helps keep temperatures relatively steady, within limits that permit life. Evaporative of the most energetic water molecules cools a surface. Ice floats because it is less dense than liquid water.
