What is the principle behind using a respirometer?
-organism that are respiring aerobically absorb oxygen and give out carbon dioxide
-if carbon dioxide produced is absorbed by sodium hydroxide solution, then the only volume change within the respirometer is due to the volume of oxygen absorbed by the organism
-if oxygen is absorbed from tube with organisms in then it has a reduced volume of air in it, decreasing pressure exerted, causing the manometer liquid to move toward the organisms due to pressure gradient
What does the distance moved by the manometer liquid show
It is proportional to respiration rate
What is the method for using this apparatus?
- After placing the coloured liquid, e.g methylene blue with detergent, into the manometer tube, the apparatus is connected with the taps open, enabling air in the apparatus to connect with the atmosphere
- The mass of living respiring organisms (e.g maggots) should be found
- With the taps still open the whole set up, with the living organisms in place, it is placed in a water bath for at least 10 minutes until it reaches the temperature of the water bath
- The syringe plunger should be near the top of the scale on the syringe barrel and it’s level noted
- The levels of coloured liquid should be marked with a pen
- Taps are closed and the apparatus left in water bath for a specific period e.g 10 minutes
- The change in level of manometer liquid can be measured and the syringe barrel depressed
- Then calculate the volume of oxygen absorbed per minute per gram of living organisms
How do you calculate the volume of oxygen absorbed per minute per gram of the living organism?
1) volume of oxygen = distance moved by liquid (mm) X cross sectional area of tube (Pi R squared)
2) rate of oxygen = calculated volume / time (sec/min/hour)
3) gram = calculated rate / weight (g)
-calculating her gram allows comparison between other respiring organisms e.g peas or germinating seeds
