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, R_T, by the rate of that same process or reaction at a temperature 10°C lower, R_T–10:

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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).

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.