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What is a Temperature Coefficient?
Does the uptake of water by seeds depend on temperature? One way to check this is to soak
seeds in water at different temperatures. The collected data then can be used to calculate the
temperature coefficient, Q10, the factor by which a physiological process or reaction rate
increases when the temperature is raised by 10°C.
Where:
Q10 = (K2 ÷ K1)10/t2 - t1
K = reaction rate at higher temperature
2
K = reaction rate at lower temperature
1
t = lower temperature
2
t = higher temperature
1
Q10 values may be used to make inferences about the physical process under investigation.
Chemical (metabolic) processes involving large protein molecules that change shape are highly
dependent on temperature and therefor have higher Q10 values, usually closer to 2 or 3. On
the other side of the Q10 values are reactions that are relatively independent of temperature.
These reactions have values closer to 1.
In an experiment done by J.D. Murphy and D.L. Noland, radish seeds (Raphanus sativum) were
weight and then placed in water at four different temperatures. After 30 minutes the seeds
were removed and reweighed after being dried off. The percent change was determined and
added to the chart below:
Temperature
5°C
15°C
25°C
35°C
% Increase in mass after 30 minutes of water uptake
18.5%
26.0%
31.0%
36.2%
Data taken from: Temperature effects on seed imbibition and leakage mediated by viscosity and membranes, Plant
Physiology 69:428-431 (1982)
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AP Biology-Krabath
Interpreting the data
1. Based on the data does the initial uptake of water by the radish seeds vary with
temperature?
2. What is the relationship between temperature and water uptake?
3. Find the Q10 values for the data at 35°C and 25°C. Repeat the calculations for the data
at 25°C and 15°C and 15°C and 5 °C. Show your calculations, undocumented answers
will not be allowed!
4. Calculate the average Q10 value
5. Do the results imply that the uptake of water by radish seeds is mainly a physical
process or a metabolic process? Back up your decision with relevant evidence.
6. Besides temperature what other independent variable could you test to see if seed
swelling is essentially a physical or a metabolic (chemical) process?
7. What about plant growth, an example being stem elongation in bean plants; would you
expect the Q10 values closer to 1 or 3? Why?
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AP Biology-Krabath