Temperature Impacts on Metabolism

Engage:

Ask students what they know about global warming and answer questions as appropriate.  Brainstorm ways in which global warming might affect different species, including people.  Ask students to think about the impacts of increased temperature on an aquatic species. 

Decide how you would prefer to allocate student responsibilities for setting up the demonstration and recording measurements. As a class, you will demonstrate that yeast produce more CO2 (i.e. respire more) at higher temperatures.

• Fill each plastic water bottle about a third of the way with warm tap water. 
• Place each water bottle in an appropriate water bath: two replicates at each of three temperatures: room temperature, ice water, and hot water (not boiling).
• Take each of the six filled balloons and secure them over the top of the bottle.
• For each, invert the balloon and swirl the water inside so that the yeast and sugar mix well. 
• Allow the bottles to stand in their water baths for the rest of the period, examining them every 5-10 minutes and observing the change in size of the balloons.  The balloons will fill with carbon dioxide from the respiration of the yeast. 

Explore:

Give students the materials, as listed above. Instruct them to design an experiment to determine the effects of temperature on the heart rate of an aquatic organism (here, daphnia magna).  They should run their test at at least two different temperatures and include an appropriate control.  Students should ask you for approval of their experimental procedure before conducting the experiment.  You may want to guide your students to measure their response variable at least three times per daphnia to get an average.  For example, their hearts beat very quickly, and it is easy to miscount. Also, some students may increase the temperature above that which the daphniacan survive (about 40 C); decide ahead of time with your students if they are comfortable with this possibility. 

Have each of the students come to the board to create a scatterplot(s) of the class data, with temperature on the x-axis and the most commonly studied variable on the y-axis (often this is heart rate). Add an additional y-axis or create a second or third scatterplot to show additional variables as needed.  Discuss the results as a class:  What does the curve look like? Is it skewed or linear?  If some students killed the daphnia at too high of a temperature, was there a long decline in the response to temperatures before the daphnia actually died or was it a steep drop-off?  Ask them whether or not we should trust these data? Explain that since each of them had a slightly different procedure, we cannot accurately compare all of these data.  However, their experiments [should be] similar enough that we can make some observations and form hypotheses for future studies.  

Explain:

Temperature affects the metabolism of daphnia, because they are cold-blooded animals; consequently their body temperature will be the same as the temperature of the water they are floating in.  The chemical reactions that occur in the cells of daphnia are dependent on certain enzymes, or proteins, to help the reactions proceed. As you increase the temperature of the water, the metabolism of the daphnia increases as well, since chemical reactions occur faster at higher temperatures. As the metabolism increases, the heart rate will speed up in order to provide enough oxygen to the cells. However, at 40 degrees Celsius, the enzymes break down, and the chemical reactions can no longer occur, so metabolism stops and the daphnia dies. Daphnia magna would very rarely if ever experience temperatures of 40 degrees in its natural environment, so this is unlikely to occur. However, they do experience temperature changes and their metabolism does increase or decrease with these changes.

            Temperature affects other organisms as well, and although you can measure stress on a larger animal, it would be unethical to test extreme temperatures.  Discuss with students what might happen to other animals in a warmer ecosystem, beyond the effects on heart rate.  What might happen to phytoplankton or zooplankton populations?  Ask students to think about how growth rate increases with temperature and whether there is an upper limit to what both plants and animals can tolerate.  What about the animals that depend on these species for food or habitat creation and maintenance (including us!)? 

This lesson leads well into the Climate Change lesson: “Climate Change and the Hudson River.” 

Extend:

            Students can read the following article to learn more about how temperature affects cold-water fish species and the ecosystems in which they live. https://downloads.globalchange.gov/toolkit/ColdWaterFish_6_9_09.pdf

Evaluate:

Students should create a graph of their results and discuss it with the class.