Laboratory #7 - RESPIRATION

Cellular respiration is the general term which describes all metabolic reactions involved in the formation of usable energy from the breakdown of nutrients. In living organisms, the "universal" source of energy is adenosine triphosphate (ATP). The first step of cellular respiration is Glycolysis, the breakdown of glucose (a six-carbon sugar) to form two molecules of pyruvate. Glycolysis takes place in the cytoplasm of the cell. The resulting pyruvate may pass through one of several pathways, depending on the organism in question. In some organisms, such as yeast, fermentation occurs. In other organisms, aerobic respiration occurs. After completing the lab, you should be familiar with the general reactions and products of aerobic respiration and fermentation.


Six fermentation tubes were prepared as outlined below.

Tube 1- glucose, water, yeast.
Tube 2- magnesium sulfate (an enzyme activator), glucose, water, yeast.
Tube 3- sodium fluoride (a poison), glucose, water, yeast.
Tube 4- sodium fluoride (but much more than in tube 3), glucose, water, yeast.
Tube 5- pyruvate (a product of glycolysis), sodium fluoride, glucose, water, yeast.
Tube 6- sodium pyruvate, glucose, water.

After the tubes were allowed to ferment for about 40 minutes, the following results were obtained.

Based on the above results, can you explain the relative amount of fermentation (as evidenced by the height of the air/CO2 space within each tube?


Two test tubes were setup to measure the consumption of oxygen during respiration. Tube #1 (shown below on the left) contained live peas that were respiring. Tube #2 (shown below on the right) contained peas that were boiled and thus not respiring. Both tubes contained potassium hydroxide which absorbs and CO2 given off. The glass capillary tube exiting the top of each test tube contained a drop of dye that either moved toward the test tube if gas was consumed or didn't move at all if no gas was consumed. Initially, the dye was positioned at the outermost edge of the capillary tube. Look closely at Tube #1 and you'll see that the dye has moved toward the tube while in Tube #2 it hasn't moved.

Tube #1 (live peas)
Tube #2 (boiled peas)


A snail was added to a beaker of water and allowed to respire for 15 minutes. An elodea plant was added to a separate beaker and also allowed to respire for 15 minutes. After the 15 minute period, the organisms were removed from the beakers and a drop of phenolphthalein was added to each beaker. Phenolphthalein remains colorless in acidic solutions, but turns pink in alkaline solutions. After the phenolphthalein was added to each beaker, sodium hydroxide (NaOH) was added drop by drop to each beaker until the contents turned pink. Since CO2 forms a weak acid when in water, the more an organism respires, the more CO2 is produced, the more acidic is the surrounding solution, and the more drops of NaOH are required to turn the solution pink. The following results were obtained for this portion of the experiment.

Control Beaker
10 drops NaOH
15 drops NaOH
12 drops NaOH

Based on the above results, which organism respired more- the snails or Elodea (assume that they were both of equal weight)?
This concludes the review for Lab 7 - Respiration.

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