CP 16 - Rate of Respiration and RQ (germinating seeds and invertibrates)

Independent Variable

Species of organism being used. (Only if using multiple species)

Dependent Variable

Distance moved by colored fluid in the manometer.

Equipment

• Sample seeds.

• Sample animals - such as woodlice.

• Potassium hydroxide solution

• Funnel (if using potassium hydroxide solution)

• Pipette

• Ruler

• Pen

• Stopwatch

• ● Respirometer - consisting of: ○ Syringe with connecting tap ○ Bung ○ Test tube ○ Capillary tubing ○ Manometer ○ Coloured liquid ○ Scale ○ Gauze

Method

1. Use the funnel to add 5 cm³ of potassium hydroxide solution to the test tube.

2. Secure the gauze in place above powder in the test tube.

3. Select the species of organism and place a known mass of them on to the gauze.

4. Set up the remainder of the respirometer.

5. Use the syringe to move the colored fluid to the end of the manometer furthest from the test tube and mark its position with a pen or record its distance from the end of the manometer by measuring with a ruler.

6. Close the 3-way tap to allow no more gas exchange to occur between the apparatus set up and the outside atmosphere and start the stopwatch immediately.

7. Measure the position of the colored fluid from its starting point every minute for 5 minutes, recording the distance moved in a suitable table. As the organisms respire, they take in oxygen, causing the pressure in the test tube to decrease which draws in air from the manometer tube; so, the volume of oxygen taken in can be calculated if the diameter of the tubing is known. Once calculated, the rate of oxygen uptake can be calculated per gram of organism and then compared between organisms.

8. Open the 3-way tap connection to the outside air and use the syringe to reset the capillary fluid.

9. Repeat steps 3-8 with any other organisms being investigated.

Apparatus