What affects the rate of cellular respiration in a plant?

Background

Plants may generate their food differently than animals do (please let us know if you have any friends with photosynthetic abilities), but they use energy within their cells using the same process animals do: cellular respiration. The processes of photosynthesis and cellular respiration are chemical reaction opposites. Photosynthesis uses light energy to build energy rich sugars, while cellular respiration unlocks the energy within sugars so it can fuel the life processes of a cell. When cellular respiration occurs, the mitochondria in a cell are breaking down sugars and releasing energy and carbon dioxide in the process.

For plants, the amount of energy they generate through cellular respiration is dependent on the amount of sugar they make through photosynthesis. However, other factors such as temperature can also affect the rate of life processes and we would expect that temperature would have some effect on the rate of photosynthesis.

This dataset can be used as evidence to answer questions about the relationship between photosynthesis and the rate of cellular respiration as well as the effect of temperature on cellular respiration.

Dataset

The data in this activity come from the work of two scientists in the Department of Environmental Biology at Australian National University. In order to study the effects of photosynthesis and temperature on cellular respiration, they placed leaves of wheat plants in an experimental chamber with grow lights. After 6.25 hours of photosynthesis, they were placed in darkness and measured the rate of respiration for 120 minutes using an infrared CO2 analyzer. They repeated this process at five different temperatures.

Variables

Temperature (Celsius): This numeric variable recorded the temperature in the test chamber during periods of light and dark. The units are degrees Celsius.

Time in the dark (min): This numeric variable is the amount of time (in minutes) since light was removed from the chamber.

CO2 release (micromol/m2/sec): This numeric variable is the rate of CO2  released. It is measured in micromols per square meter per second. Because CO2 is a product of cellular respiration, increases or decreases of this variable can show us changes in the rate of cellular respiration

Activity

1. Make a graph showing Rate of CO2 release on the Y-axis and Time in the dark (min) on the X-axis. Show Temperature (Celsius) as your Z variable to color code you data point by the temperature in the five test chambers. Check the box at the right to Connect dots.

2. What is the general trend in the Rate of CO2 release that occurs in the two hours after the plant is placed in the dark?

3. Is this trend in the Rate of CO2 release the same in the trials for all temperatures? Explain.

4. What is the the effect of temperature on cellular respiration? Use the graph as evidence to support your answer.

5. Photosynthesis requires light energy to occur, but cellular respiration does not. Why do you think the Rate of CO2 release decreases over the two hours of darkness? 

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