Chapter 3 Water and the Fitness of the Environment PDF

# Chapter 3 Water and the Fitness of the Environment ## Overview: The Molecule That Supports All of Life - Water is the biological medium on Earth. - All living organisms require water more than any other substance. - Most cells are surrounded by water, and cells themselves are about 70%-95% water...

# Chapter 3 Water and the Fitness of the Environment ## Overview: The Molecule That Supports All of Life - Water is the biological medium on Earth. - All living organisms require water more than any other substance. - Most cells are surrounded by water, and cells themselves are about 70%-95% water. - The abundance of water is the main reason the Earth is habitable. ## Why does the abundance of water allow life to exist on the planet Earth? - The polarity of water molecules results in **hydrogen bonding** - opposite ends have opposite charges. - **Four of water's properties that facilitate an environment for life are:** - **Cohesive behavior** - Ability to moderate temperature: Stable. - Expansion upon freezing: Less dense ice floats. - Versatility as a solvent. ## Hydrogen bonds between water molecules - The oxygen atom is more electronegative, which means it attracts electrons more strongly than the hydrogen atoms. - This creates a slightly negative charge near the oxygen atom and a slightly positive charge near the hydrogen atoms. - The opposite charges on different water molecules create hydrogen bonds between them. ## Water Properties: - **Cohesion:** hydrogen bonds hold water molecules together. - Plants: transport of water against gravity. - **Adhesion:** attraction between different substances, ie water and plant cell walls. - **Surface tension:** hard it is to break the surface of a liquid; related to cohesion. ## Moderation of Temperature - Water absorbs heat from warmer air and releases stored heat to cooler air. Stable. - Water can absorb or release a large amount of heat with only a slight change in its own temperature = **high specific heat**. - **Kinetic energy:** energy of motion. - **Heat:** total amount of kinetic energy due to molecular motion. - **Temperature:** heat intensity from average kinetic energy. ## Heat Units - **Calorie:** heat required to raise the temperature of 1 g of water by 1°C. - **“Calories” on food packages** - **kilocalories (kcal), 1 kcal = 1,000 cal.** - **Joule (J) energy unit; 1 cal = 4.184 J** ## Specific Heat - **Specific heat:** amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1°C. - Water = 1 cal/g/°C; high specific heat = **STABLE** - **High specific heat** → hydrogen bonds - Heat is absorbed → hydrogen bonds break. - Heat is released → hydrogen bonds form. - The high specific heat of water minimizes temperature fluctuations within limits that permit life. ## The effect of a large body of water on climate - Stable - Shown is a diagram of various cities and their temperatures, illustrating the moderating effects of the Pacific Ocean on coastal temperatures. <start_of_image> Diagrams were omitted from the response. ## Evaporative Cooling - **Evaporation:** liquid to gas. - **Heat of vaporization:** heat a liquid must absorb for 1 g to be converted to gas. - **Evaporative cooling:** as a liquid evaporates, its remaining surface cools. - Helps stabilize temperatures in organisms and bodies of water. ## Insulation of Bodies of Water by Floating Ice - **Ice floats:** hydrogen bonds in ice are more “ordered,” less dense. - Greatest density at 4°C. - If ice sank, all bodies of water would eventually freeze solid → life impossible. ## The Solvent of Life - Solution: homogeneous mixture of substances. - **Solvent:** dissolving agent & **Solute:** dissolved substance. - **Aqueous solution**: water is the solvent; polarity & hydrogen bonds. - **Hydration shell:** ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules. - Water can also dissolve nonionic polar molecules and large ionic, polar molecules, proteins. - **Colloid:** stable suspension of fine particles in a liquid. ## Solute Concentration in Aqueous Solutions - Biochemical reactions occur in water. - Collisions of molecules. - Concentration of solutes in aqueous solution. - **Molecular mass:** sum of all masses of all atoms in a molecule. - **Avogadro's number:** 6.02 x 1023 daltons = 1 g. - **1 mole (mol) = 6.02 x 1023**. - **Molarity (M): moles of solute / L of solution.** ## Acids and Bases and pH - **pH = -log [H+]** - **Acidic** < 7, **basic** (alkaline) < 7, or **neutral** = 7. - H2O + H2O → H3O+ + OH- - **Acid:** increases H+; **Base:** reduces H+. - Adding certain solutes, called acids and bases, modifies the concentrations of H+ and OH-, and changes pH. - Drastically affect the chemistry of a cell. - Biological fluids have pH values: 6 to 8. - **Buffer:** mixture of a weak acid and a weak base that minimize pH changes when an acid or base is added to a solution. ## The pH scale - A diagram was omitted from the response - There is a table of different substances with their pH values. ## Threats to Water Quality on Earth - **Acid precipitation:** to rain, snow, or fog with a pH lower than 5.6; **Acid rain:** pH < 5.6. - Caused by mixing of different pollutants with water in the air. - Fall at some distance from the source of pollutants. - Damage life in lakes and streams. - Acid precipitation on soil chemistry are contributing to forest decline. ## Acid precipitation and its effects on a forest - This diagram shows a graphic representation of the effect of acid rain on trees. It shows a natural forest in green, with trees in a red-colored range showing damage over time, and some barren trees in brown. The acid rain pH goes from normal rain, pH 5.6 to more acidic rain. ## Human activities - Human activities, burning fossil fuels, threaten water quality. - Fossil fuel combustion releases CO2. - Greenhouse effect. - **Acidification of the oceans:** decrease in the ability of corals to form calcified reefs ## What is the effect of carbonate ion concentration on coral reef calcification? - Shown is a diagram of a coral reef with an experiment. The graph illustrates a decreasing calcification rate as the carbonate ion concentration increases. ## Evidence of Water - Two images of a rocky surface are shown, one labeled "Surface of Earth", the other "Surface of Mars". - The image of Earth's surface shows water in a lake with the texture of the rocky earth visible under the water. - The image of Mars' surface shows a red colored surface with many cracks (and some blue). ## You should now be able to: 1. List and explain the four properties of water that emerge as a result of its ability to form hydrogen bonds. 2. Distinguish between the following sets of terms: hydrophobic and hydrophilic substances; a solute, a solvent, and a solution. 3. Define acid, base, and pH. 4. Explain how buffers work.