Question

(a) Using the data for 35°C and 25°C, calculate Q₁₀ for water uptake by radish seeds. Repeat the calculation using the data for 25°C and 15°C and the data for 15°C and 5°C. (b) What is the average Q₁₀? (c) Do your results imply that the uptake of water by radish seeds is mainly a physical process or a chemical (metabolic) process? (d) Given that the Q₁₀ for the change in the viscosity of water is 1.2–1.3, could the slight temperature dependence of water uptake by seeds be a reflection of the slight temperature dependence of the viscosity of water?

Short answer

(a)The Q₁₀values for the three temperature ranges are 1.16, 1.19, and 1.40.

(b) The average Q₁₀value is 1.25.

(c) Water uptake by radish seeds is a physical process.

(d) Yes, the slight temperature dependence of water uptake reflects slight temperature dependence of water viscosity.

Step-by-step solution

Explanation for (a)

The temperature coefficient is calculated using the following formula:

$Q_{10}={\left(\frac{k_2}{k_1}\right)}^{\frac{10}{t_2-t_1}}$

Where t₂ and t₁ are higher and lower temperatures, respectively, and k₂ and k₁ are reaction rates at t₂ and t₁, respectively. Here, k₂ and k₁ refer to the percent increase in mass due to water uptake at t₂ and t₁, respectively.

Substituting the values of k₂ and k₁ for 35°C and 25°Cfrom the table in the equation,

$\begin{array}{l}{Q}_{10}={\left(\frac{36.2}{31.2}\right)}^{\frac{10}{35-25}}\\ ={\left(\frac{36.2}{31.2}\right)}^{\frac{10}{10}}\\ =1.16\end{array}$

Similarly, Q₁₀ for 25°C and 15°C is calculated as:

$\begin{array}{l}{Q}_{10}={\left(\frac{31.0}{26.0}\right)}^{\frac{10}{25-15}}\\ ={\left(\frac{31.0}{26.0}\right)}^{\frac{10}{10}}\\ =1.19\end{array}$

Q₁₀for 15°C and 5°C is calculated as:

$\begin{array}{l}{Q}_{10}={\left(\frac{26.0}{18.5}\right)}^{\frac{10}{15-5}}\\ ={\left(\frac{26.0}{18.5}\right)}^{\frac{10}{10}}\\ =1.40\end{array}$

Explanation for (b)

The average Q₁₀ is calculated by taking the mean of the three Q₁₀values of the three temperature ranges.

$\begin{array}{l}\mathrm{Average} Q_{10}=\frac{1.16+1.19+1.40}{3} \\ =1.25\end{array}$

Explanation for (c)

Chemical processes such as protein shapes have higher Q10 values such as 2 or 3 because they are dependent on temperature. However, many physical processes are temperature independent and have lower Q10 values that are close to 1.

The uptake of water by radish seeds is a physical process because Q10 values range from 1.16 to 1.40, close to 1.

Explanation for (d)

The slight temperature dependence of water uptake reflects the slight temperature dependence of the water viscosity because both these water-related processes have almost the same Q10.