Chapter 3: Water and Life PDF

Chapter 3: Water and Life Chemistry life Campbell Biology, 12th Edition and / 3.1. Polar covalent bonds in water molecules result in hydrogen The water molecule is a polar molecule: The bonding opposite...

Chapter 3: Water and Life Chemistry life Campbell Biology, 12th Edition and / 3.1. Polar covalent bonds in water molecules result in hydrogen The water molecule is a polar molecule: The bonding opposite ends have opposite charges Polarity allows water molecules to form hydrogen bonds with each other What is the cause of polarity in water ?  Loading… Water has high specific heat  Concept 3.2: Four emergent properties of water contribute to Earth’s fitness for life Surface high tension Four of water’s properties that facilitate an environment for life: Cohesive behavior.. Ability to moderate temperature. Expansion upon freezing.. Versatility as a solvent.  Cohesion Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion. Loading… Cohesion helps the transport of water against gravity in plants. Adhesion of water to plant cell walls also helps to counter gravity.- Surface tension is a measure of how hard it is to break the surface of a liquid Surface tension is related to cohesion  Moderation of Temperature Water absorbs heat from warmer air and releases stored heat to cooler air. Water can absorb or release a large amount of heat with only a slight change in its own temperature.  Water’s High Specific Heat The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºC. Water’s high specific heat minimizes temperature fluctuations to within limits that permit life Heat is absorbed when hydrogen bonds break Heat is released when hydrogen bonds form  Evaporative Cooling Evaporation is transformation of a substance from liquid to gas. Heat of vaporization is the heat a liquid must absorb for 1 gram to be converted to gas. As a liquid evaporates, its remaining surface cools, a process called evaporative cooling. Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water.  Insulation of Bodies of Water by Floating Ice Ice floats in liquid water because hydrogen bonds in ice are more “ordered,” Loading… making ice less dense. If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth.  The Solvent of Life A solution is a liquid that is a homogeneous mixture of substances A solvent is the dissolving agent of a solution The solute is the substance that is dissolved Water is a versatile solvent due to its polarity An aqueous solution is one in which water is the solvent  Water is an effective solvent because it readily forms hydrogen bonds. When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules, a hydration shell  Hydrophilic and Hydrophobic Substances A hydrophilic substance is one that has an affinity for water. A hydrophobic substance is one that does not have an affinity for water.  Solute Concentration in Aqueous Solutions Most biochemical reactions occur in water. Chemical reactions depend on collisions of molecules and therefore on the concentration of solutes in an aqueous solution.  Molecular mass is the sum of all masses of all atoms in a molecule. Numbers of molecules are usually measured in moles, with one mole being 6.02 x 1023 molecules. Molarity is the number of moles of solute per liter of solution  I/ Concept 3.3: Dissociation of water molecules leads to acidic and basic conditions that affect living organisms A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other: The hydrogen atom leaves its electron behind and is transferred as a proton, or hydrogen ion (H+). The molecule with the extra proton is now a hydronium ion (H3O+). The molecule that lost the proton is now a hydroxide ion (OH-). The process can be described in a simplified way as the separation of a water molecule into a hydrogen ion (H+) and a hydroxide ion (OH-). Though statistically rare, the dissociation of water molecules has a great effect on organisms. Changes in concentrations of H+ and OH- can drastically affect the chemistry of a cell.  Effects of changes in pH Concentrations of H+ and OH- are equal in pure water. Adding certain solutes, called acids and bases, modifies the concentrations of H+ and OH- Biologists use something called the pH scale to describe how acidic or basic (the opposite of acidic).  Acids and Bases An acid is any substance that increases the H+ concentration of a solution. A base is any substance that reduces the H+ concentration of a solution.  The pH Scale The pH of a solution is determined by the relative concentration of hydrogen ions. Acidic solutions have pH values less than 7. Basic solutions have pH values greater than 7 Most biological fluids have pH values in the range of 6 to 8.  Buffers The internal pH of most living cells must remain close to pH 7. Buffers are substances that minimize changes in concentrations of H+ and OH- in a solution. Most buffers consist of an acid-base pair that reversibly combines with H+.  The Threat of Acid Precipitation Acid precipitation refers to rain, snow, or fog with a pH lower than 5.6. Acid precipitation is caused mainly by the mixing of different pollutants with water in the air. Acid precipitation can damage life in lakes and streams. Effects of acid precipitation on soil chemistry are contributing to the decline of some forests.