Describe and carry out investigations, using simple respirometers, to determine the RQ of germinating seeds or small invertebrates (e.g. blowfly larvae)

SouravOctober 31, 2024

Answered step-by-step

Investigation: Determining the Respiratory Quotient (RQ) of Germinating Seeds using a Simple Respirometer

Option A: Germinating Seeds
Option B: Small Invertebrates (e.g., Blowfly Larvae)

Investigation Overview:

• Aim: To determine the Respiratory Quotient (RQ) of germinating seeds or small invertebrates (e.g., blowfly larvae) using a simple respirometer.
• Principle: Measure the volume of CO2 produced and O2 consumed over a set period, calculating RQ as CO2/O2.
• Equipment (Simple Respirometer Setup):
  • Eudiometer tube or a large test tube
  • Rubber bung
  • Delivery tube
  • Absorbent for CO2 (e.g., soda lime)
  • Absorbent for water vapor (e.g., calcium chloride)
  • Thermometer
  • Germinating seeds or blowfly larvae in a small container
  • Measuring cylinder
  • Stopwatch

Procedure for Both Options:

Setup:

1. Prepare the Respirometer:
   • Fill the bottom of the eudiometer/test tube with a layer of water.
   • Add a small amount of soda lime (CO2 absorbent) above the water, separated by a small piece of paper or a coffee filter.
   • Place a layer of calcium chloride (water vapor absorbent) on top.
2. Prepare the Organism Container:
   • For Germinating Seeds: Place a measured amount of germinating seeds in a small, breathable container (e.g., a mesh-covered mini container).
   • For Blowfly Larvae: Gently place a measured number of blowfly larvae in a similar small, ventilated container.

Experiment:

1. Initial Reading:
   • Attach the organism container to the rubber bung, ensuring an airtight seal.
   • Quickly attach the bung to the eudiometer/test tube, noting the initial water level.
2. Incubation:
   • Place the setup in a water bath or a thermally stable environment to maintain a constant temperature (recorded with a thermometer).
   • Allow the system to equilibrate for a short period (e.g., 10 minutes).
3. Measurement:
   • Start the stopwatch and record the water level at regular intervals (e.g., every 10 minutes) over a set period (e.g., 1 hour).
   • The movement of the water level indicates the net gas exchange (CO2 produced – O2 consumed).
4. Final Reading:
   • After the set period, record the final water level.

Calculations:

1. Volume of Gas Exchanged:
   • Calculate the total volume of gas exchanged based on the change in water level, considering the eudiometer’s dimensions.
2. CO2 Produced (VCO2):
   • Since CO2 is absorbed, the initial decrease in water level (before it stabilizes or increases slightly due to O2 consumption) represents the net CO2 production. However, for simplicity and given the setup, we’ll consider the total gas exchanged as a proxy for VCO2 – VO2.
3. O2 Consumed (VO2):
   • Assuming the RQ for germinating seeds is approximately 1 (carbohydrate metabolism) or using the blowfly larvae’s expected RQ value (if known), estimate VO2 from VCO2 (or the proxy VCO2 – VO2).
   • For a more accurate VO2, use a separate O2 measurement method if available.
4. Respiratory Quotient (RQ) Calculation:
   • RQ = VCO2 / VO2

Example Calculations (Hypothetical Data):

• Germinating Seeds:
  • VCO2 – VO2 (Net Gas Exchange): 10 mL (Positive indicates more CO2 produced than O2 consumed, but for simplicity, we use this as a proxy)
  • Assumed VO2 (for calculation purposes): Given RQ ≈ 1 for carbohydrates, let’s assume VO2 ≈ VCO2
  • Estimated VCO2: 10 mL (Simplified assumption for demonstration)
  • RQ ≈ 10 mL (VCO2) / 10 mL (VO2) ≈ 1.00
• Blowfly Larvae:
  • VCO2 – VO2: 8 mL
  • Assumed VO2 (based on metabolic pathways, e.g., mixed substrate usage): Let’s assume an RQ ≈ 0.85 for estimation, VO2 ≈ 9.41 mL (if VCO2 = 8 mL, calculated from assumed RQ)
  • Estimated VCO2: 8 mL (Used directly as it represents net CO2 production in this simplified model)
  • RQ ≈ 8 mL (VCO2) / 9.41 mL (VO2) ≈ 0.85

Note: These calculations are highly simplified and based on hypothetical data. Actual experiments would require more precise measurements, potentially separate measurements for O2 consumption, and consideration of the experimental environment’s impact on gas exchange.

Safety and Ethical Considerations:

• Handle organisms gently and humanely.
• Ensure adequate ventilation in the experimental area.
• Follow proper disposal procedures for biological materials.
• Obtain necessary ethical approvals for working with living organisms.