On Fig. 8.1, use the letter A together with a label line to indicate where the Krebs cycle takes place.
Name the structure labelled B on Fig. 8.1 that is part of the inner mitochondrial membrane.
The inner mitochondrial membrane is the location of oxidative phosphorylation. Explain how the structure of the inner mitochondrial membrane is related to its function.
The activity of succinate dehydrogenase, an enzyme in the Krebs cycle, is used to estimate the rate of respiration in the mitochondria. The redox reaction catalysed by succinate dehydrogenase is shown in Fig. 8.2 as $\text{succinate} \xrightarrow{\text{succinate dehydrogenase}} \text{fumarate}$ with electrons $e^{-}$ released. A redox indicator can be used to measure succinate dehydrogenase activity. Name a redox indicator and explain why it can be used for this purpose.
Fig. 8.3 shows a ground squirrel, Ictidomys tridecemlineatus. In winter, the ground squirrel curls into a spherical shape underground and remains asleep for long periods. At this time, it alternates between two states: torpor, in which body temperature is kept at $10\,^{\circ}\text{C}$, and euthermia, in which body temperature is kept at $37\,^{\circ}\text{C}$. Scientists used succinate dehydrogenase activity to examine the rate of mitochondrial respiration in ground squirrels. Mitochondria were isolated from liver and muscle samples of ground squirrels. Respiration rate was measured at different succinate concentrations and at temperatures corresponding to torpor ($10\,^{\circ}\text{C}$) and euthermia ($37\,^{\circ}\text{C}$). The findings are shown in Fig. 8.4.
Describe the trends visible in Fig. 8.4.
Explain the difference in respiration rates between liver at $37\,^{\circ}\text{C}$ and muscle at $37\,^{\circ}\text{C}$.
During torpor in ground squirrels, muscle tissue uses more energy than liver tissue. Suggest one reason for this.