The rate of respiration can be determined by monitoring the rate of oxygen consumption or...

The rate of respiration can be determined by monitoring the rate of oxygen consumption or carbon dioxide production:

In an experiment, the change in gas volume using a respirometer containing 25 nongerminating pea seeds was measured at two temperatures (10 and 20°C). The experiment was conducted in the dark so that photosynthesis did not occur. The CO2 produced during cellular respiration was removed by the reaction of CO2with potassium hydroxide (KOH) to form solid potassium carbonate (K2CO3). In this way, only the oxygen consumed was measured. The results are as follows:

(a) Determine the number of moles of oxygen consumed after 20 minutes. Assume the atmospheric pressure is 1 atm.

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(b) Determine the rate constant for each of the data assuming first order kinetics. Compare your results to those obtained for germinating seeds (see Example 3–2).

Example 3?2

The rate of respiration can be determined by monitoring the rate of oxygen consumption or carbon dioxide production:

 (3–8)

In an experiment, the change in gas volume using a respirometer containing 25 germinating pea seeds was measured at two temperatures (10 and 20°C). The experiment was conducted in the dark so that photosynthesis did not occur. The CO2 produced during cellular respiration was removed by the reaction of CO2 with potassium hydroxide (KOH) to form solid potassium carbonate (K2CO3). In this way, only the oxygen consumed was measured. The results are as follows:

1. Determine the number of moles of oxygen consumed after 20 minutes. Assume the atmospheric pressure is 1 atm.

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2. Determine the rate constant for each of the data assuming first order kinetics. Explain your results.

Solution

1. The volumes of oxygen consumed after 20 minutes were 0.78 mL at 10°C and 0.93 mL at 20°C. The number of moles of oxygen can be calculate using the ideal gas law:

PV = nRT

Solving for n:

n = PV/RT

at 10°C:

at 10°C:

2. Using the same approach as employed in (1), the number of moles of oxygen can be calculated for the two data sets:

The natural log of the number of moles can then be plotted vs. time to determine the slopes and the rate constant:

Data Source: http://www.scribd.com/doc/7570252/AP-Biology-Lab-Five-Cell-Respiration

http://www.biologyjunction.com/Cell%20Respiration.htm

As shown in the figure the rate constant for the seeds at 10°C was 0.09 min−1 and 0.14 min−1 at 20°C. The increase is to be expected as the metabolic activity of the seeds would increase with increasing temperature.