Ap Biology Frq #3
FRQ #3 a.) The first property of water is its polarity. A water molecule is formed by one oxygen atom covalently bonded to two hydrogen atoms. The electronegativity of the oxygen atom creates an unequal sharing of electrons between the O and H atoms of the molecule. This also gives water the ability to form hydrogen bonds between the slightly negative oxygen atom and the slightly positive hydrogen atom. Water has a high specific heat due to the hydrogen bonds. Because of this, water requires a large amount of energy to raise its temperature by just one degree. The polar nature of water allows the water molecules to attach to one another this is called cohesion. Cohesion gives water its surface tension where the water molecules bind to each other making it difficult for the surface to be broken. b.) Water is known as the universal solvent. Its polarity allows it to ionize materials by breaking down ionic bonds as well as polar covalent bonds. Water is able to equalize solute concentrations in a cell by the process of osmosis. Osmosis is the movement of water and solute molecules across a semipermeable membrane down a concentration gradient to equal out the concentration levels on both sides. The high specific heat of large bodies of water can moderate the temperatures of the environment by absorbing heat from the atmosphere during the day to keep the weather cooler and releasing it back into the air at night to keep the air from getting too cold, therefore keeping the temperatures on land relatively moderate. Ice is less dense than liquid water because as a liquid the molecules have a lot energy and are moving past each other and running into each other, but as water cools down the molecules have less energy and the hydrogen bonds become more stable and form a crystalized structure which spaces out the molecules from one another making the ice less dense than liquid water. Because ice is less dense it floats on the top of lakes and ponds and acts as an