Answers to Review Questions

1. I will not agree to patent the invention. The first law of thermodynamics states that one form of energy can be converted to other forms of energy, but it also states that energy can be neither created nor destroyed. An invention that did not require fuel would not have source energy and it would be unable, according to the first law, to create anew the energy it required. Mechanical devices cannot create energy from nothing. Therefore, such an invention would be impossible and unworthy of a patent.

3. Entropy is the name for the amount of disorder in the universe. Equilibrium is the condition of maximum entropy. When a system has attained maximum entropy- when it is as random as it can be- it has reached equilibrium. When equilibrium has been reached, no more changes can occur unless energy is obtained from the outside.

5. Vitalism suggested that living organisms did not have to obey the laws of the universe like the First Law. After experimentation with living organisms, it quickly became apparent that living organisms are no more able to create energy from nothing than are mechanical devices. It was found that the energy for life comes directly or indirectly from the radiant heat and light of the sun. The realization that living organisms obeyed the First Law (the Law of the Conservation of Energy) was the beginning of the end of vitalism. It meant that life was no longer exempt from the laws of the universe. Living organisms also obey the Second Law of Thermodynamics by increasing the randomness of the part of the universe outside the system of the living organism. Thus, while order within the living organism increases (entropy decreasing), the remainder of the universe outside the living organism exhibits a larger increase in entropy. Thus, the sum of entropy both inside and outside the living organism is positive, satisfying the requirements of the Second Law. The increased entropy of the surroundings is largely due to the conversion of useful energy into useless energy (heat) which then contributes to the disorder in the rest of the universe.

7. A fire, once started, will generally burn anything that it touches. It speeds up the oxidation of paper raising the overall energy of all of the paper molecules. Metabolic oxidation, on the other hand, is selective about what is being oxidized. The cell generally burns fuel molecules like glucose and not cellular machinery like proteins and DNA. Enzymes, which are responsible for catalyzing all reactions in the cell, including oxidative reactions are extremely specific with respect to the substrates on which they can act. For each step in metabolic oxidation, only the appropriate substrate reacts. Oxidation of glucose by fire releases the energy stored in glucose all at once resulting in the emission of significant amounts of heat and light. This would not be good for a living organism since the heat and light given off would be likely to damage a living organism severely. Living organisms are much more efficient in extracting energy from glucose. Living organisms enhance their specificity either by capturing as much energy as possible from oxidative reactions or by spending as little energy as possible to catalyze reactions that consume energy. When glucose is oxidized in the cell, energy is released from it in a stepwise fashion, a little bit at a time. At particular points in that sequence, some of the energy that is released is captured and stored in ATP or other similar molecules. While some energy is given off as heat during such a process, the process harnesses energy much more efficiently than does a fire.

9. Reactions that are thermodynamically favorable may occur very slowly or seemingly not at all. The reason for this is that most reactions have an energy barrier, the activation energy, that must be surmounted before the reaction can be completed. This is the energy required to break bonds, which is usually the first step in such chemical reactions. Very few substrate molecules, at any given time, have an energy content sufficient to surmount the activation energy. Thus, such reactions occur at very low rates.

11. Glycolysis is widely considered to be the first metabolic pathway to evolve for a few different reasons. First, it is a universal energy-harvesting process of life and has been shown to be the most widespread metabolic pathway in the living world. It is common to every living thing and is similar or identical in every type of living cell and thus appears to be very primitive. It is thought that it may have been present in the first living cell and then may have been passed on to all successful progeny of that first cell.

13. Glucose goes into glycolysis and it carries all of the chemical energy entering the pathway. At the end of glycolysis, there are two pyruvate molecules for every glucose that entered glycolysis. Furthermore, there is a net gain of two ATPs for every glucose molecule metabolized. Finally, two reduced NADH molecules are produced for every glucose molecule. They will be used in the electron transport system to make ATPs if oxygen is available. At the end of glycolysis, portions of the energy originally stored in glucose can be found in the ATPs, reduced NADH molecules, and pyruvate molecules produced by glycolysis.

15. The inner mitochondrial membrane is analogous to the dam. The H+ ions (protons) concentrated between the two mitochondrial membranes is analogous to the water behind the dam. The turbine in a hydroelectric dam is analogous to the mitochondrial ATP synthase.

17. The light-dependent reactions cannot occur in a test tube using only the plant cells' juices. The reason for this is that the pigments that absorb the light and the electron transport system are located in the thylakoid membranes. Furthermore, intact thylakoid membranes are required in order to set up the proton gradient between the thylakoid lumen and the stroma of the chloroplast that is used to produce ATP. Finally, the chloroplast ATP synthase enzyme that synthesizes the ATP is embedded in the thylakoid membranes as well and extracts the energy from the proton gradient as the protons move back into the stroma from the thylakoid lumen.

19. Rubisco (ribulose biphosphate carboxylase) fixes gaseous CO2 out of the atmosphere and attaches it to a sold 5-carbon skeleton (ribulose biphosphate). Without it, plants could not manufacture the food they need to sustain their lives and the lives of all of the organisms that depend on plants directly or indirectly for their nourishment.