Chapter 2 - Section 2.2 - Study Guide - Assess Your Learning Outcomes - Page 74: 1

The biologically important properties of water arise primarily from its unique molecular structure, which includes its polarity and bond angle. Water molecules are composed of two hydrogen atoms covalently bonded to one oxygen atom. Here's how these properties contribute to water's significance in biology: 1. Polarity: - Water molecules are polar, which means they have an uneven distribution of electrons, resulting in a partial negative charge (δ-) on the oxygen atom and partial positive charges (δ+) on the hydrogen atoms. - This polarity leads to the formation of hydrogen bonds between neighboring water molecules. Hydrogen bonds are relatively weak, but they are responsible for many of water's crucial properties in biology. 2. Solvent Properties: - Water's polarity allows it to be an excellent solvent for polar and ionic compounds. It can dissolve a wide range of molecules, including salts, sugars, and acids, which is vital for biological processes like cell metabolism, nutrient transport, and waste removal. 3. Cohesion and Adhesion: - Water molecules are attracted to each other due to hydrogen bonding. This cohesion results in high surface tension, allowing small organisms like insects to walk on water. - Adhesion is the attraction between water molecules and other polar molecules, such as those found in the walls of plant cells. This property enables water to move against gravity in plants, facilitating nutrient transport. 4. High Specific Heat Capacity: - Water has a high specific heat capacity, meaning it can absorb and store a significant amount of heat energy without a substantial temperature change. - This property helps maintain stable temperatures in organisms and their environments, preventing rapid temperature fluctuations that could be detrimental to life. 5. High Heat of Vaporization: - Water requires a substantial amount of energy to change from a liquid to a gas due to hydrogen bonding. This property is essential for organisms that use evaporative cooling to regulate body temperature. 6. Expansion Upon Freezing: - Water expands when it freezes because of the formation of a crystalline lattice held together by hydrogen bonds. - This expansion property is critical because it prevents bodies of water from freezing solid, which would be detrimental to aquatic life. 7. Excellent Heat Conductor: - Water's ability to conduct heat is vital in many biological processes, helping to distribute thermal energy within organisms. In summary, the polarity of water molecules and the bond angle between hydrogen and oxygen contribute to a range of biologically important properties, including its role as a solvent, its ability to maintain temperature stability, its capacity to support life through cohesive and adhesive forces, and its role in various metabolic processes. These properties make water a fundamental molecule for life as we know it.

The biologically important properties of water arise primarily from its unique molecular structure, which includes its polarity and bond angle. Water molecules are composed of two hydrogen atoms covalently bonded to one oxygen atom. Here's how these properties contribute to water's significance in biology: 1. Polarity: - Water molecules are polar, which means they have an uneven distribution of electrons, resulting in a partial negative charge (δ-) on the oxygen atom and partial positive charges (δ+) on the hydrogen atoms. - This polarity leads to the formation of hydrogen bonds between neighboring water molecules. Hydrogen bonds are relatively weak, but they are responsible for many of water's crucial properties in biology. 2. Solvent Properties: - Water's polarity allows it to be an excellent solvent for polar and ionic compounds. It can dissolve a wide range of molecules, including salts, sugars, and acids, which is vital for biological processes like cell metabolism, nutrient transport, and waste removal. 3. Cohesion and Adhesion: - Water molecules are attracted to each other due to hydrogen bonding. This cohesion results in high surface tension, allowing small organisms like insects to walk on water. - Adhesion is the attraction between water molecules and other polar molecules, such as those found in the walls of plant cells. This property enables water to move against gravity in plants, facilitating nutrient transport. 4. High Specific Heat Capacity: - Water has a high specific heat capacity, meaning it can absorb and store a significant amount of heat energy without a substantial temperature change. - This property helps maintain stable temperatures in organisms and their environments, preventing rapid temperature fluctuations that could be detrimental to life. 5. High Heat of Vaporization: - Water requires a substantial amount of energy to change from a liquid to a gas due to hydrogen bonding. This property is essential for organisms that use evaporative cooling to regulate body temperature. 6. Expansion Upon Freezing: - Water expands when it freezes because of the formation of a crystalline lattice held together by hydrogen bonds. - This expansion property is critical because it prevents bodies of water from freezing solid, which would be detrimental to aquatic life. 7. Excellent Heat Conductor: - Water's ability to conduct heat is vital in many biological processes, helping to distribute thermal energy within organisms. In summary, the polarity of water molecules and the bond angle between hydrogen and oxygen contribute to a range of biologically important properties, including its role as a solvent, its ability to maintain temperature stability, its capacity to support life through cohesive and adhesive forces, and its role in various metabolic processes. These properties make water a fundamental molecule for life as we know it.