AP Biology Exam Review Unit 1 Questions with Verified Answers

AP Biology Exam Review Unit 1 Questions with Verified Answers How does hydrogen bonding allow for cohesive behavior in water? At any given moment, many of the molecules in liquid water are linked by multiple hydrogen bonds, which collectively hold the substance together and make water more structured than other liquids. This allows for adhesion (the clinging of one substance to another) and a relatively high surface tension (a measure of how difficult it is to stretch or break the surface of a liquid). Using the properties of water, describe how water can move up a capillary tube to move from the roots to the leaves in a plant. Cohesion due to hydrogen bonding contributed to the transport of water and dissolved nutrients against gravity in plants. Water from the roots reached the leaves through a network of water-conducting cells; as water evaporates from a leaf, hydrogen bonds cause water molecules leaving the veins to tug on molecules farther down, and the upward pull is transmitted through the water-conducting cells all the way to the roots. Using the properties of water, describe how a water strider can walk on water. The hydrogen bonds in water give it an unusually high surface tension, making it behave as though it were coated with an invisible film. A water strider can take advantage of water's resistance to surface breakage in order to walk across it. How does hydrogen bonding allow for the ability to moderate temperature in water? The ability of water to stabilize temperature steams from its relatively high specific heat (the amount of heat that must be absorbed or released for 1g of that substance to change its temperature by 1°C). This is because heat must be absorbed in order to break hydrogen bonds and released in order to form them; so much heat is needed to disrupt these molecules before water molecules can speed up. How does hydrogen bonding allow for expansion upon cooling in water? Water is one of the few substances that are less dense as a solid than as a liquid, meaning that ice floats on water. Instead of contracting and becoming denser as it solidifies, water expands; as water begins to freeze (as the temperature falls from 4°C to 0°C), more and more if it's molecules are moving too slowly to break hydrogen bonds and become locked into a crystalline lattice (each water no like is hydrogen-bonded to four partners). Why is water considered a polar molecule? The unequal sharing of electrons and water's V-like shape make it a polar molecule, since it's overall charge is unevenly distributed: the oxygen region of the molecule has a partial negative charge and each hydrogen has a partial positive charge). What is an aqueous solution? Why is water considered the universal solvent? An aqueous solution is one in which the solute is dissolved in water; water is the solvent. Water is a very versatile solvent due to the polarity of the molecule. Water is capable of dissolving ionic compounds such as salt (by surrounding individual ions with molecules of opposing charges to separate and shield them from one another) and polar molecules like sugars (by surrounding each of the solute molecules and form hydrogen bonds with them). Such (biological) molecules include blood, plant sap, and cellular liquid. Basically, it considered a universal solvent because almost anything dissolves in it, and because it dissolves more substances than any other solvent. What is a hydrogen bond? One of the weak chemical bonds that are central to the chemistry of life; a hydrogen bond is characterized by the non-covalent attraction between a hydrogen and an electronegative atom. When a hydrogen atom is covalently bonded to an electronegative atom, the hydrogen atom has a partial positive charge that allows it to be attracted to a different electronegative atom nearby. Typically, it is attracted to nitrogen or oxygen. Where are hydrogen bonds found in water? Hydrogen bonds are located in between different water molecules, connecting the partial positive charge of one of the hydrogen atoms from one water molecule to the partial negative charge of the oxygen molecule of another water molecule. Where are hydrogen bounds found in DNA? How many hydrogen bonds are found between each complementary base pairing? In DNA, hydrogen bonds exist between the opposing bases of complementary base pairs. This means that adenine (A) in one strand opposes thymine (T) in the other strand, and guanine (G) opposes cytosine (C). The A-T pair forms