For Problems 2.12.35, do the following: Draw a picture of the system. Name an extensive property that can be counted. Label the system, surroundings, and system boundary. State the time period of interest. Justify. Identify the system as open, closed, or isolated and state why. Identify the system as steady-state or dynamic and state why. Identify whether the system has a reaction and/or energy interconversion and state why. Should an algebraic, differential, or integral equation be used to describe the system? State why. Is the selected extensive property conserved in this system? State why. (Note: There can be more than one correct answer; it depends on how you set up the system.) Problems are identified as pertaining to the areas of mass (M), energy (E), charge (C), or momentum (P).

2.34 (M) Runners rely on muscles to propel them as they run. Muscles require a continuous supply of oxygen and glucose for contraction. Metabolism of these reactants generates carbon dioxide and lactate. Consider as the system the thigh muscle of a person during a 1000-m race. You wish to model glucose during the race.

2.35 (M) The small intestine is an important organ in the digestive system. With the help of various enzymatic secretions from the pancreas and liver, pro- teins, fats, and other nutritional components are broken down in the small intestine and are then absorbed through the walls of the small intestine into the blood. For example, proteins are enzymatically broken down into peptides. Consider as the system the small intestine of a person for the four hours following the start of dinner and track protein as the extensive prop- erty of interest.