Lab 5   Cell Respiration

 Introduction
Cellular respiration is a series of enzyme-mediated reactions that release the energy from carbohydrates.  It begins in the cytosol with glycolysis and is completed within the mitochondria.  Cellular Respiration can be summarized with the following equation: 

C6H12O6 + 6O2 → 6CO2 + 6H2O + 686 kilocalories of energy/mole of glucose oxidized

Cellular respiration could be measured in several different ways, but in this experiment oxygen consumption is used.  To do this, it uses a number of the physical laws of gases including the equation, PV = nRT, where P stands for pressure, V for volume, n for the number of molecules, R for the gas constant, and T for temperature.  This law shows the many relationships between these factors and how they affect each other.

This experiment compares respiration rates in germinating and non-germinating peas.  Germination is the growth processes of a seed.  It requires a lot of energy to break the seed coat and as it continues to grow this energy need increases.  Respiration is required to access this energy so as the seed germinates its respiration rates increase.  Non-germinating seeds, however, are dormant and use very little respiration.  Some respiration must occur in order for the seed to live. 

Hypothesis
The rate of cellular respiration will be greater in germinating peas than in dry peas, and temperature will have a direct effect on this rate.

Materials
This lab required a room temperature bath and a 10C bath, ice, a 100-mL graduated cylinder, 50 germinating peas, paper towels, 150 mL of water, dry peas, beads, six vials with attached stoppers and pipettes, absorbent cotton, 5-mL pipette, 15% KOH, non-absorbent cotton, masking tape, and a timer. 

Methods
A room temperature bath and a 10C bath were prepared.  A 100-mL graduated cylinder was filled with 50 mL of water.  Then, 25 germinating peas were added and the amount of displaced water was determined and recorded.  The peas were then removed and placed on a paper towel until needed for Respirometer 1. The graduated cylinder was then refilled with 50 mL of water.  25 dry peas were added and beads were added until the volume equaled that of the germinating peas.  The peas and beads were removed and placed on a paper towel for use in Respirometer 2.           After refilling the graduated cylinder with 50 mL of water, beads were added until the volume again equaled that of the germinating peas.  They were removed and placed in a paper towel for use in Respirometer 3.
The above procedures were repeated to prepare a second set of germinating peas, dry peas and beads, and beads for use in Respirometers 4, 5, and 6.  The respirometers were prepared next by first placing a small wad of absorbent cotton in the bottom of each respirometer and saturating it with 15% KOH, being careful not to get any on the sides of the vial.  Next, a piece of non-absorbent cotton was placed on top of the KOH-soaked cotton.  The first set of germinating peas, peas and beads, and beads were added to Respirometers 1, 2, and 3.  Then the second set was added to Respirometers 4, 5, and 6.
A masking tape sling was created for each of the water baths to hold the respirometers out of the water during equilibration.  Respirometers 1, 2, and 3 were placed in the room-temperature bath, and Respirometers 4,5,and 6 were placed in the 10C water bath.  The respirometers were allowed to equilibrate for 10 minutes and then were immersed entirely in the water bath. They were checked for leaks and an initial reading was taken.  Then additional readings were taken every 5 minutes for 20 minutes. 

Results

Temp

(C)

Time

(min)

Beads Alone

Germinating Peas

Dry Peas and Beads

Reading at time X

Diff.

Reading at time X

Diff.

Corrected Diff.

Reading at time X

Diff.

Corrected Diff.

10

Initial - 0