Water and the Fitness of the Environment PDF

Water and the Fitness of the Environment https://www.thestatesman.com northeast-india-sees-heavy-ex Lecture Outcomes Appreciate the role of covalent polar bonds in water molecules and formation of hydrogen bonds as the basis o...

Water and the Fitness of the Environment https://www.thestatesman.com northeast-india-sees-heavy-ex Lecture Outcomes Appreciate the role of covalent polar bonds in water molecules and formation of hydrogen bonds as the basis of water’s properties Understand how four properties of water contribute to Earth’s suitability for life How acidic and basic pH conditions affect living organisms  Three-quarters of Earth’s surface is covered by water. Although most of this water is in liquid form, water is also present on Earth as a solid (ice) and a gas (water vapor). All living beings familiar to us are mostly made out of water and usually live in environments dominated by water. Most cells contain about 70% to 95% water. Why is water so important to life? What makes it so special? Polar covalent bonds in water molecules result in hydrogen bonding Water is shaped like a wide “V” with its two hydrogen atoms joined to the oxygen atom by single covalent bonds. Oxygen is more electronegative than hydrogen, so the electrons of the covalent bonds spend more time closer to oxygen than to hydrogen; these are polar covalent bonds. This unequal sharing of electrons and water’s V- like shape make it a polar molecule, meaning that its overall charge is unevenly distributed: The oxygen region of the molecule has a partial negative charge (δ-), and each hydrogen has a partial positive charge (δ+). https://socratic.org/questions/5a7c5ca8b72cff 1fc646  The properties of water arise from attractions between oppositely charged atoms of different water molecules: The slightly positive hydrogen of one water molecule is attracted to the slightly negative oxygen of a nearby water molecule. These attractions are called hydrogen bonds and are not as strong as covalent bonds When water is in its liquid form, the hydrogen bonds are weak and last for a short time before they break New hydrogen bonds between new water molecules are always being forming, breaking, and forming again Therefore, at any moment, a large percentage of all the water molecules are hydrogen-bonded to their neighbors Four Properties of Water Make it Crucial to Support Life 1. Cohesion Cohesion = sticking together Hydrogen bonds between water molecules make them cohesive (stay close together) This helps trees draw water from the roots to the leaves Water molecules in leaves at the top pull on the water molecules below them which pull on the water molecules below them all the way down to the roots, as shown next slide Surface Tension Surface tension is the ability of water molecules to stay together, and resist external forces trying to break them apart For example, some insects can walk on a water surface because the water molecules hold onto each other through hydrogen bond and resist the force exerted by the legs https://youtu.be/kx02qT2p5uk?si=JwyE1UFdIPjOE- 1D&t=37 Water has a higher surface tension than most other liquids 2. Moderation of Temperature Water moderates air temperature by absorbing heat from air that is warmer and releasing the stored heat to air that is cooler Water is effective as a heat bank because it can absorb or release a relatively large amount of heat with only a slight change in its own temperature Why is water able to do that? Why is that important for living beings? To understand this capability of water, we must first look briefly at heat and temperature Heat and Temperature Anything that moves has kinetic energy, the energy of motion. Atoms and molecules have kinetic energy because they are always moving The faster a molecule moves, the greater its kinetic energy Heat = measurement of the total kinetic energy for the whole amount of matter Temperature is the average kinetic energy of the molecules in matter https://www.physics.utoronto.ca /~jharlow/teaching/everyday06/ reading10.htm  The cup of tea has a higher temperature than the swimming pool, because the molecules in tea have more kinetic energy on average. However, the swimming pool has more heat because it has more molecules, and the total kinetic energy of all the molecules in the swimming pool is more than the total kinetic energy of all the molecules in the small cup of tea  When two objects of different temperature are brought together, heat passes from the warmer to the cooler object until the two are the same temperature. An ice cube cools a drink not by adding coldness to the liquid, but by absorbing heat from the liquid as the ice itself melts.