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Lab Session : Cellular Respiration 

(The Krebs Cycle and Electron Transport Chain)

    The EP-M 5/2 class of Mr. Derrick Thompson did a lab about the Cellular Respiration- (The Krebs Cycle and Electron Transport Chain). In this activity, the students grouped themselves and in each group, one volunteer executed the experiment. Each group had 2 beakers with 4 drops of bromothymol blue diluted with 10 ml of water.


    To start the experiment, the volunteers placed the straw into the beaker, touching the bottom. When the timer said go, the volunteers slowly blew into the Bromothymol blue solution until it changed color. Students recorded this time in their table, under the ‘resting’ column.


    Next, the volunteers performed a physically demanding exercise for 2 – 3 minutes, after which they blew into a straw, like before but into a new Bromothymol blue solution of the same concentration. Students recorded the amount of time that the solution took to change color, like before.


    Exercise of the sort done by students’ causes an increase in aerobic cellular respiration, or cellular respiration that requires oxygen and produces carbon dioxide (CO2) as a waste product.


    The carbon dioxide (CO2) produced reacts with water to form carbonic acid (H2CO3). 


    The carbonic acid reacts with the bromothymol blue solution, changing its color from blue to yellow.


   What does it mean?


    This demonstration proves to us that our bodies are giving off carbon dioxide as waste products when we perform aerobic exercises. This carbon dioxide is produced in the Krebs cycle part of aerobic cellular respiration, in the mitochondria of our cells.


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