Overview of Lab 5: Respiration

Purpose: To measure the rate of cellular respiration in germinating peas by observing the volume of gas surrounding the peas at various intervals.

Materials:

• A total of 6 respirometers
• glass beads
• germinating seeds
• non-germinating seeds
• water bath with 10 degrees water
• water bath with 25 degrees water (room temperature)
• KOH solution
• absorbent cotton
• non-absorbent cotton
  

Instructions:

1. Soak the absorbent cotton with KOH in each of the three vials.
2. Cover with non-absorbent cotton.
3. Add 25 germinating peas to vial 1
4. Add 25 non-germinating peas to vial 2 and cover them with enough glass beads to that it is at the same volume as vial 1.
5. Add enough glass beads to vial 3 to have the same volume of vials 1 and 2. Vial 3 is the control.
6. Cap each vial with a stopper, seal the respirometor, and add weights to each vial (so they don't float in the water).
7. Place the three vials in the container with water of 10 degrees, with the tips of the vials resting on a sling. Allow the vials to equilibrate for a few minutes.
8. Lower the tips into the water, and take an initial reading.
9. Take readings from each respirometer for 15 minutes with 5 minute intervals. This is done by reading the water graduations on the pipettes. The reading is a measurement of oxygen consumption and therefore an indirect measurement of repiratory rate.
   
10. Repeat steps 7,8,9 with a second set of vials in a water bath of 25 degrees.

Results:

• Water will enter the pipettes and travel a short distance. As respiration occurs, O2 is consumed in the vials, and pressure in the vials and pipettes drops. When the pressure drops, additional water from the water bath will enter the pipettes.
  

• The experiment should yield results which follow the generalizations,

1. As temperature decreases/increases respiration decreases/increases.
2. Germinating seeds respire more.

Cellular respiration is the breakdown of glucose with oxygen to produce carbon dioxide, water, and energy

The volume of gas can be affected by both the use of oxygen gas and the product of carbon dioxide, carbon dioxide is removed by using potassium hydroxide. KOH reacts with O2 to produce solid K2CO3.

Because CO2 gas is removed from the reaction, the gas volume change can only be effected by consumption of oxygen (as a result of respiration), change in temperature, and change in atmospheric pressure.

Questions

1. What was the purpose of the beads?

Glass beads are added to maintain equal volumes so that oxygen gas can be measured accurately.

2. What happens to the temperature of gas when the pressure increases (assuming volume remains constant)?

The temperature of gas increases when the pressure increases.

3. What happens to the volume of gas when the temperature decreases (assuming pressure remains constant?

The volume of gas decreases when the temperature of gas decreases.