BIOLOGY 101 CHAPTER 3: Water and Life: The Molecule that supports all Live Water and Life: The Molecule that Supports all Life CONCEPTS: • 3.1 Polar covalent bonds in water molecules result in hydrogen bonding • 3.2 Four emergent properties of water contribute to Earth's suitability for life • 3.3 Acidic and basic conditions affect living organisms Water and Life: The Molecule that Supports all Life OVERVIEW: • The physical properties of water are dictated by the laws of thermodynamics The First Law of Thermodynamics Energy cannot be created or destroyed, it can only be transformed The Second Law of Thermodynamics The total entropy of an isolated system always increases over time or… High energy systems spontaneously change to lower energy systems Water and Life: The Molecule that Supports all Life 3.1 Polar covalent bonds in water molecules result in hydrogen bonding: • A water molecule is shaped like a wide V, with two hydrogen atoms joined to an oxygen atom by single polar covalent bonds. • Because oxygen is more electronegative than hydrogen, a water molecule is a polar molecule in which opposite ends of the molecule have opposite charges. ✓ Polar molecules have a separation of charges, having both positively and negatively charged regions Water and Life: The Molecule that Supports all Life 3.1 Polar covalent bonds in water molecules result in hydrogen bonding: • A water molecule is shaped like a wide V, with two hydrogen atoms joined to an oxygen atom by single polar covalent bonds. • Because oxygen is more electronegative than hydrogen, a water molecule is a polar molecule in which opposite ends of the molecule have opposite charges. ✓ The oxygen region of the molecule has a partial negative charge (-), and the hydrogen regions have a partial positive charge (+). Water and Life: Organisms depend on the cohesion of water molecules 3.2 Four emergent properties of water contribute to Earth's suitability for life: 1. Cohesion of Water Molecules (Surface Tension and Transpiration) • Many organisms depend on surface tension and the cohesion of water 2. Moderation of Temperature (Specific Heat & Heat of Vaporization) • Properties of water reduce large temperature changes in the environment 3. Ice Floats and Insulates (Density of Ice) • Because ice floats, lakes and oceans do not freeze 4. Effective Solvent (polar substance) • The polar nature of water allows biological molecules to be transported and stored in living organisms Water and Life: The Molecule that Supports all Life 3.2 Four emergent properties of water contribute to Earth's suitability for life: • Water has a variety of unusual properties because of the attraction between polar water molecules. ✓ The slightly negative regions of one water molecule are attracted to the slightly positive regions of nearby water molecules, forming hydrogen bonds. • When water is in its liquid form, its hydrogen bonds are very fragile, about one-twentieth as strong as covalent bonds. • Hydrogen bonds form, break, and re-form with great frequency • Each hydrogen bond lasts only a few trillionths of a second, but the molecules continuously form new hydrogen bonds with a succession of partners. • At any given instant, a substantial percentage of all water molecules are hydrogen-bonded to their neighbors Water and Life: The Molecule that Supports all Life 1 3.2 Four emergent properties of water contribute to Earth's suitability for life: • Collectively, hydrogen bonds hold water together, a phenomenon called cohesion. • Cohesion among water molecules plays a key role in transporting water and dissolved nutrients against gravity in plants. Water and Life: Organisms depend on the cohesion of water molecules 3.2 Four emergent properties of water contribute to Earth's suitability for life: 1. Cohesion: Surface tension, a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion. ✓ Water has a greater surface tension than most other liquids because hydrogen bonds among surface water molecules resist stretching or breaking the surface. ✓ Water behaves as if covered by an invisible film. ✓ Some animals can stand, walk, or run on water without breaking the surface ➢ Plants use cohesion to transport water (transpiration / capillary action) Water and Life: The Molecule that Supports all Life 1 3.1 Polar covalent bonds in water molecules result in hydrogen bonding: • Cohesion among water molecules plays a key role in transporting water and dissolved nutrients against gravity in plants. (This type of cohesion is called transpiration) • Water molecules move up from the roots to the leaves of a plant through water-conducting vessels. • As water molecules evaporate from a leaf, other water molecules from vessels in the leaf are pulled up and replace them. • This upward pull is transmitted down to the roots. Water and Life: The Molecule that Supports all Life 1 3.1 Polar covalent bonds in water molecules result in hydrogen bonding: • Cohesion among water molecules plays a key role in transporting water and dissolved nutrients against gravity in plants. (This type of cohesion is called transpiration) • Water molecules move up from the roots to the leaves of a plant through water-conducting vessels. • As water molecules evaporate from a leaf, other water molecules from vessels in the leaf are pulled up and replace them. • This upward pull is transmitted down to the roots. o Transpiration is aided by capillary action (wicking). This is when water flows into narrow spaces through the forces of cohesion and surface tension Water and Life: Water moderates temperatures on Earth 2 3.2 Four emergent properties of water contribute to Earth's suitability for life: 2. Water moderates air temperatures by absorbing heat from warmer air that it contacts • This is how evaporative cooling works: ✓ Strictly speaking, water does not ‘cool’ the air. The warm air transfers heat to the water. 2nd Law of Thermodynamics Water and Life: Water moderates temperatures on Earth 2 3.2 Four emergent properties of water contribute to Earth's suitability for life: 2. Water moderates air temperatures by absorbing heat from warmer air and releasing the stored heat to cooler air. • Water can absorb or release relatively large amounts of heat with only a slight change in its own temperature. • Atoms and molecules have kinetic energy, the energy of motion, because they are always moving. • The faster a molecule moves, the more kinetic energy it has. ▪ Heat is a measure of the total quantity of kinetic energy due to molecular motion in a body of matter. Water and Life: Water moderates temperatures on Earth 2 3.2 Four emergent properties of water contribute to Earth's suitability for life: • Temperature measures the intensity of heat in a body of matter due to the average kinetic energy of molecules. ✓ As the average speed of molecules increases, a thermometer records an increase in temperature. • Heat and temperature are related but not identical. ✓ Heat depends in part on the matter’s volume, while temperature is the average kinetic energy of molecules, regardless of volume. ❖ Heat is a measure of the total quantity of kinetic energy due to molecular motion in a body of matter. Water and Life: Water moderates temperatures on Earth 2 3.2 Four emergent properties of water contribute to Earth's suitability for life: • Evaporative cooling works because the water absorbs kinetic energy (Heat), but most of that energy does not remain kinetic! • The kinetic energy (heat from the air) is instead used to break hydrogen bonds in water (these bonds will immediately reform!) • This way, water can absorb heat energy and not increase its own temperature (kinetic energy) The heat energy is used to break H-bonds, So the energy transferred to water isn’t kinetic energy The resulting water does not warm up Water and Life: Water moderates temperatures on Earth 2 3.2 Four emergent properties of water contribute to Earth's suitability for life: • In most biological settings, temperature is measured on the Celsius scale (°C). ✓ At sea level, water freezes at 0°C and boils at 100°C. ✓ Human body temperature is typically 37°C. • One convenient way to measure heat energy is the calorie (cal). ✓ One calorie is the amount of heat energy necessary to raise the temperature of 1 gram of water by 1°C. ✓ A calorie is released when 1 g of water cools by 1°C. Water and Life: Water moderates temperatures on Earth 2 3.2 Four emergent properties of water contribute to Earth's suitability for life: • Water stabilizes temperature because it has a high specific heat. ✓ The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1°C. • Water has an unusually high specific heat (1 cal) compared to other substances. ✓ Water resists changes in temperature because of its high specific heat. ✓ In other words, water absorbs or releases a relatively large quantity of heat for each degree of temperature change. Water and Life: Water moderates temperatures on Earth 2 3.2 Four emergent properties of water contribute to Earth's suitability for life: • Water’s high specific heat is due to hydrogen bonding. ✓ Heat (Kinetic Energy) is absorbed by water, but it does not remain as kinetic energy (heat). Water and Life: Water moderates temperatures on Earth 2 3.2 Four emergent properties of water contribute to Earth's suitability for life: • Water’s high specific heat is due to hydrogen bonding. ✓ Heat (Kinetic Energy) is absorbed by water, but it does not remain as kinetic energy (heat). The energy is used to break hydrogen bonds instead. This means the average kinetic energy of the water does not increase very much Water and Life: Water moderates temperatures on Earth 2 3.2 Four emergent properties of water contribute to Earth's suitability for life: • Water’s high specific heat affects Earth as a whole as well as individual organisms.