Water and the Fitness of the Environment (for life) Chapter 3

Why is water important to life? Most cells are surrounded by water Most cells are surrounded by water Cells are 70 to 95% water Cells are 70 to 95% water Water is only substance that exists in all 3 states (solid, liquid and gas) naturally on earth Water is only substance that exists in all 3 states (solid, liquid and gas) naturally on earth

The Polarity of Water and Hydrogen bonding Polar molecules: elements in the molecule have different electronegativities (a difference greater than.4) and one atom pulls harder in the tug of war for electrons. The electrons spend more time around the more electronegative atom. This results in a polar molecule. One side is negatively charged and one side is positively charged. Polar molecules: elements in the molecule have different electronegativities (a difference greater than.4) and one atom pulls harder in the tug of war for electrons. The electrons spend more time around the more electronegative atom. This results in a polar molecule. One side is negatively charged and one side is positively charged. The polarity allows the water molecules to form hydrogen bonds: week molecular attractions between H δ+ and a negatively charged atom. The polarity allows the water molecules to form hydrogen bonds: week molecular attractions between H δ+ and a negatively charged atom. Each H 2 O can form H bonds with up to 4 neighboring molecules. Each H 2 O can form H bonds with up to 4 neighboring molecules. 03_02WaterStructure_A.swf 03_02WaterStructure_A.swf 03_02WaterStructure_A.swf

4 Emergent Properties of Water 1. Cohesion: water molecules held together by the H bonds. 1. Cohesion: water molecules held together by the H bonds. Allows transport of water in plants against gravity Allows transport of water in plants against gravity : clinging of one substance to another: water to cell wall in plants Adhesion: clinging of one substance to another: water to cell wall in plants 03_03WaterTransport_A.swf 03_03WaterTransport_A.swf 03_03WaterTransport_A.swf Surface Tension: water has high surface tension due to H bonds between molecules on the surface. Surface Tension: water has high surface tension due to H bonds between molecules on the surface.

Moderation in Temperature Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air. Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air. Water has a high specific heat (amount of heat change for 1 g of substance to change by 1 °C), so it can absorb or release large amounts of heat with small temperature changes. Water prevents large temperature fluctuations in coastal biomes. Due to H bonding! Water has a high specific heat (amount of heat change for 1 g of substance to change by 1 °C), so it can absorb or release large amounts of heat with small temperature changes. Water prevents large temperature fluctuations in coastal biomes. Due to H bonding! Atoms and molecules have kinetic energy, the energy of motion, because they are always moving. Atoms and molecules have kinetic energy, the energy of motion, because they are always moving. Heat is a measure of the total quantity of kinetic energy due to molecular motion in a body of matter. Heat is a measure of the total quantity of kinetic energy due to molecular motion in a body of matter. Temperature measures the intensity of heat in a body of matter due to the average kinetic energy of molecules. Temperature measures the intensity of heat in a body of matter due to the average kinetic energy of molecules.

Fig. 3-5 San Diego 72° 40 miles Pacific Ocean 70s (°F ) 80s 90s 100s Santa Barbara 73° Los Angeles (Airport) 75° Burbank 90° San Bernardino 100° Riverside 96° Santa Ana 84° Palm Springs 106°

Vaporizaiton/Evaporation The amount of heat required for 1 g of a substance to change from liquid to a gas. Very high for water b/c the H bonds must be broken. The amount of heat required for 1 g of a substance to change from liquid to a gas. Very high for water b/c the H bonds must be broken. As the water turns to gas and evaporates, the heat is taken with it and the solution (person) cools = evaporative cooling! As the water turns to gas and evaporates, the heat is taken with it and the solution (person) cools = evaporative cooling! Sweating and release of water from plants cools terrestrial organisms. Sweating and release of water from plants cools terrestrial organisms. About 580 cal of heat are required to evaporate 1 g of water at room temperature; this is fairly high (break H bonds) About 580 cal of heat are required to evaporate 1 g of water at room temperature; this is fairly high (break H bonds) content/uploads/2009/07/sweating.jpg _cI/AAAAAAAAAhc/Ukd0GHhnYxM/s320/trans piration.gif

Water expands when it freezes Ice Hydrogen bonds are stable Liquid water Hydrogen bonds break and re-form Hydrogen bond

Water is insulated by floating ice Water is unusual because it is less dense as a solid than as a cold liquid. Water is unusual because it is less dense as a solid than as a cold liquid. All other substances contract as they freeze, but water expands. All other substances contract as they freeze, but water expands. At temperatures above 4°C, water behaves like other liquids, expanding as it warms and contracting as it cools. At temperatures above 4°C, water behaves like other liquids, expanding as it warms and contracting as it cools. When water reaches 0°C, water becomes locked into a crystalline lattice, with each water molecule bonded to a maximum of four partners. As the water warms to 0°C, the H bonds are disrupted. When water reaches 0°C, water becomes locked into a crystalline lattice, with each water molecule bonded to a maximum of four partners. As the water warms to 0°C, the H bonds are disrupted. If ice sank, eventually all ponds, lakes, and even the ocean would freeze solid and marine life would die off. If ice sank, eventually all ponds, lakes, and even the ocean would freeze solid and marine life would die off. Instead, the surface layer of ice insulates liquid water below, preventing it from freezing and allowing life to exist under the frozen surface

The Solvent of Life

Water is the solvent of life – dissolves other substances to form aqueous solutions Water is the solvent of life – dissolves other substances to form aqueous solutions Effective at dissolving ionic and polar substances Effective at dissolving ionic and polar substances EX: salt water EX: salt water Water – solvent – does the dissolving Water – solvent – does the dissolving NaCl – solute – gets dissolved NaCl – solute – gets dissolved Hydrophilic – water loving Ionic bonds or polar molecules Hydrophobic – water fearing Covalent bonds and non-polar molecules

Biology and the Mole. Remember that the amount of a substance in chemical reaction is measured in moles. Remember that the amount of a substance in chemical reaction is measured in moles. One mole is 6.02 x of any substance. One mole is 6.02 x of any substance. The mass of the substance off the periodic table in grams is equal to one mole. The mass of the substance off the periodic table in grams is equal to one mole. We measure concentration with Molarity We measure concentration with Molarity M= Moles of solute/Liters of solution M= Moles of solute/Liters of solution To make a 1 molar (1M) solution of sucrose (C 12 H 22 O 11 ), we would slowly add water to 342 g (molar mass) of sucrose until the total volume was 1 liter and all the sugar was dissolved. Sometimes it is necessary to heat a solution to dissolve all of the solute. To make a 1 molar (1M) solution of sucrose (C 12 H 22 O 11 ), we would slowly add water to 342 g (molar mass) of sucrose until the total volume was 1 liter and all the sugar was dissolved. Sometimes it is necessary to heat a solution to dissolve all of the solute.

Acids and Bases & their affect on life A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other: 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 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 (H 3 O + ), though it is often represented as H + The molecule with the extra proton is now a hydronium ion (H 3 O + ), though it is often represented as H + The molecule that lost the proton is now a hydroxide ion (OH – ) The molecule that lost the proton is now a hydroxide ion (OH – ) H H H H H H H H O O OO 2H 2 OHydronium ion (H 3 O + ) Hydroxide ion (OH – )

Acid Vs. Base An acid increases the H + conc. of a solution An acid increases the H + conc. of a solution Acids have a pH between 0 and Acids have a pH between 0 and A base reduces the H + conc. of a solution Some bases accept H + ions, others release OH - in solution. Bases have a pH between and In any solution, the product of the H + and OH − concentrations is constant at 10 −14. In a neutral solution, [H + ] = 10 −7 M and [OH − ] = 10 −7 M pH = − log [H + ] or [H + ] = 10 −pH In a neutral solution, [H+] = 10−7 M, and the pH = 7. Values for pH decline as [H + ] increase

Buffers and biological systems Buffers minimize changes in pH by accepting H + ions when needed or donating H + ions Buffers minimize changes in pH by accepting H + ions when needed or donating H + ions Organisms use buffers to maintain homeostasis. Organisms use buffers to maintain homeostasis. Blood pH is 7.4, carbonic acid helps to maintain this pH Blood pH is 7.4, carbonic acid helps to maintain this pH Figure 5 This diagram shows the diffusion directions for H +, CO 2, and O 2 between the blood and the muscle cells during exercise. The resulting concentration changes affect the buffer equilibria, shown in the upper right-hand corner of the diagram (yellow)