Q10 is a measure of temperature sensitivity

Even between 0°C and 40°C, changes in body temperature create problems for animals. Most *biochemical reactions and the physiological processes they are involved in are temperature-sensitive, going faster at higher temperatures. The temperature sensitivity of a reaction or process can be described in terms of Q10, a factor calculated by dividing the rate of a process or reaction at a certain temperature, RT, by the rate of that same process or reaction at a temperature 10°C lower, RT–10:

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*connect the concepts As discussed in Key Concept 8.5, increases in temperature increase reaction rates because reactant molecules have more kinetic energy. Enzymes that control rates of biochemical reactions in metabolic pathways are influenced by temperature as well.

Q10 can be measured for a simple biochemical reaction or for a complex physiological process, such as rate of oxygen consumption. If a reaction or process is not temperature-sensitive, it has a Q10 of 1. Most biological Q10 values are between 2 and 3. A Q10 of 2 means that the reaction rate doubles as temperature increases by 10°C, and a Q10 of 3 indicates a tripling of the rate over a 10°C temperature range (Figure 39.7).

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Figure 39.7 Q10 and Reaction Rate The larger the Q10 of a reaction or process, the faster its rate rises in response to an increase in temperature.

Notice that the Q10 values (except for Q10 = 1) plotted in Figure 39.7 produce curves rather than straight lines. This is because temperature increases in additive intervals (10, 20, 30, etc.) but reaction rates increase in a multiplicative fashion (2, 4, 8, 16, 32, etc.). Such curvilinear plots are common in biological data.

Changes in body temperature can disrupt an animal’s physiology because not all of the biochemical reactions that constitute the metabolism of an animal have the same Q10. These biochemical reactions are linked together in complex networks: the products of one reaction are the reactants for other reactions. Because different reactions have different Q10’s, changes in tissue temperature will shift the rates of some reactions more than others, disrupting the overall network. Therefore, to maintain homeostasis, organisms compensate for or prevent changes in body temperature.