Figure 3. Effect of citric acid on the rate of the reaction catalyzed by PFK. All reactions were carried out in the presence of 1 mM F6P and 0.5 mM ATP. (a) Describe the transfer of energy that occurs in the reaction shown in Figure 1. (b) Identify a dependent variable in the experiment shown in Figure 2. Based on the data shown in Figure 2, justify the use of the substrate F6P at a concentration of 1 mM when the scientists performed the experiments shown in Figure 3. Based on data shown in Figure 2 for reactions performed in the absence of AMP, describe the relative difference between the reaction rate at 15°C and at 25°C when the concentration of F6P is 0.3 mM AND when the concentration of F6P is 0.8 mM. Based on Figure 3, calculate the fold change in the reaction rate (how many times higher or lower the reaction rate is) at 25°C when the concentration of citric acid is increased from 0 mM to 4 mM. (c) State a null hypothesis for the experiments shown in Figure 3. The scientists claim that the concentration of citric acid in cells regulates the rate of glycolysis by the cells. Support the scientists' claim using biological principles and the data provided. Predict the effect on the active site of PFK if PFK is maintained at 75°C for 20 minutes prior to starting the reaction. (d) Some aquatic organisms that live in cold environments similar to that of the crabs have multiple forms of certain enzymes that catalyze reactions at various temperatures. Explain how having multiple forms of the enzymes would contribute to the fitness of these organisms. Both adult and juvenile red king crabs can be found in ocean water of a different salinity and osmolarity than their body tissues are. Explain why it is important to the crabs that they can regulate the osmolarity of their tissues.