151 disc-22fa HW1

151-3 Introductory Biology - Discussion Homework 1 Week of September 12, 2022 Name: Katie Scheer Reminder: Submit your homework on Canvas by the start of your scheduled discussion section! Please use a different font color so that your answers stand out. 1. The summary formula for photosynthesis is 6CO 2 + 6H 2 O―›C 6 H 12 O 6 + 6O 2 a. How many molecules of carbon dioxide and water would a plant have to use to produce 3 molecules of glucose (C 6 H 12 O 6 )? 18 CO2 and 18 H2O b. How many moles of carbon dioxide and water would a plant have to use to produce 2 moles of glucose? 12 CO2 and 12 H2O 2. O 2 and NH 3 are both small covalent molecules found in cells. NH 3 is extremely soluble in the aqueous environment of the cell, while O 2 is relatively insoluble. What is the basis for this difference in solubility between the two molecules? In reaching your answer, draw the structures of the molecules as valence shell diagrams (as in Chapter 2 of the text – see figure 2.6 for an example). What types of interactions might each molecule have with water? Ammonia is a polar molecule like water, and polar substances are more soluble in water. O2 is not polar. 3. Life as we know it could not exist without water. All the chemical reactions of life occur in aqueous solution. Water molecules are polar and are capable of forming hydrogen bonds with other polar or charged molecules. As a result, water has the following properties: ● H 2 O molecules are cohesive; they form hydrogen bonds with each other. ● H 2 O molecules are adhesive; they form hydrogen bonds with polar surfaces. ● Water is a liquid at normal physiological (or body) temperatures. ● Water’s greatest density occurs at 4°C. ● Ions and polar molecules dissolve in water due to hydrogen bonding. Explain how these properties of water are related to the five phenomena described below. More than one property may be used to explain a given phenomenon. Phenomena How are the properties of water related? During the winter, air temperatures in the northern United States can remain below 0°C for months; however, the fish and other animals living in the lakes survive. Density - ice floats. Unlike most other solids, ice expands and becomes less dense than the water. The fish are able to survive in the water below the ice. Many substances—for example, salt (NaCl) and sucrose—dissolve quickly in water. Adhesive - the partial positive charges of the substances react with the partial negative charges of the water molecules, and vice versa. Ions and polar molecules dissolve in water due to h-bonding