OLLI Class 1 Summary

Water exists in three states on planet earth: solid, liquid and gas. What allows this is water’s “hydrogen bonds” which are very short-lived attractions between adjacent water molecules. Water is a polar covalent bonded molecule. The Oxygen does not share electrons with the two hydrogens equally, resulting in the oxygen side of the molecule being negative and the two hydrogen sides being positive. So the positive hydrogen sides are attracted briefly to the negative oxygen side of another nearby water molecule. They just keep changing unless the temperature at sea level drops to 0 Celsius in which case the water molecules organize into a highly structured and low-density solid form, ice. Few molecules exist in all three states (solid, liquid and gaseous) at “common” temperatures and pressures of earth’s ecosystems. There was a discussion of methane hydrate (methane’s solid form deep under the ocean’s bottom.

Water’s high heat capacity is due to its hydrogen bonds. Water heats slowly and it also cools slowly. This stability makes it an ideal molecule to comprise 70% of animal tissues. The high heat capacity is why we observe “Lake Effect Snow” in January when cold Arctic air blows over warmer waters of large bodies of water which have not yet reached their coldest temperatures of the year. 

Water’s cohesion property means water like to stick to other water molecules. Water’s adhesive properties means that water likes to adhere to other materials. These two properties are a result of its hydrogen bonds. It is these two properties that allow trees to pull water (and dissolved nutrients) from the ground all the way to the highest leaves as the leaves transpire through their stomata (pores on underside of leaves). 

Hydrogen bonds hold the two strands of DNA in every one of your chromosomes together until the time that the chromosomes need to duplicated. Since life on this planet evolved in a watery medium DNA has acquired a double stranded, tilted, helical structure to protect the DNA from water and water-dissolved chemicals which can damage the DNA. 

We covered photosynthesis’s “light reaction” where pigments in the chloroplast’s internal membranes capture a photon of light, transfer the photon’s energy from one pigment to another. A water molecule is split into H+, an electron and Oxygen. The electron lost from water is used to replace an electron lost from an excited photo-pigment. In the end two energy rich molecules are synthesized by plant during the light reaction: NADPH and ATP. These two energy rich molecules are used to assemble glucose in photosynthesis’s “dark-reaction” where the plants take up CO2. In the end, plants lower CO2, add Oxygen to the environment and build plant tissue from glucose and minerals they uptake with their water. No water, no photosynthesis!