respirometre

• how do you calculate the volume of oxygen taken up in a respirometre?

  • by using the diameter of the capillary tube r (cm)
  • and the distance moved by the manometer fluid h (cm) in a minute using the formula: πr2h
• what is included in the components of a respirometre?

  • experimental tube (with glass beads) and control tube (with respiring seeds/other organism)
  • the glass beads have the same volume/mass as the seeds in the experimental tube
  • temperature controlled water bath
  • stop watch
  • test tubes
  • soda lime pellets (to absorb the carbon dioxide produced)
  • manometre fluid (distance travelled of the fluid can be used to calculate the rate of oxygen consumption)

  
• state the general aims of using a respirometer

  • Respirometers are used to measure and investigate the rate of oxygen consumption during aerobic respiration in organisms
  • The experiments usually involve organisms such as seeds or invertebrates
  • By adding the apparatus to a thermostatically controlled water bath the effect of temperature on the rate of respiration can be investigated
• what is a limitation of using a respirometer?

  it's for measuring the rate of aerobic respiration. It cannot be used to measure the rate of anaerobic respiration as no oxygen is consumed during anaerobic respiration,
• why does the rate of respiration decrease at very high and very low temperatures?

  • at extremely high temperatures, proteins become denatured and are unable to carry out their function.
  • At low temperatures, molecules and enzymes don’t collide very frequently as they don’t have a lot of energy. 
  • the rate of respiration relies on the action of enzymes
• how can the results of a respirometer be analysed?

  • The rate of oxygen consumption (cm3 min-1) is often taken as the rate of respiration for organisms
  • The different volumes of oxygen consumed obtained for the different temperatures can be presented in table or graph form to show the effects of temperature

  
• what information is needed to compare the data from the oxygen uptake for one batch of seeds to data from another type of bean?

  the mass of the seed batch
• how would you use a respirometer to calculate the oxygen consumption of an invertabrae? (PPQ)

  • mass of invertebrate and mass of beans the same
  • safe and ethical use of invertebrates e.g. add screen so that animal(s) cannot touch the muslin bag
  • big syringe needed (5–10 cm3)
  • keep temperature constant
  • keep light constant
  • set mass of soda lime (especially if using control tube)
  • measuring distance moved by coloured, red liquid at regular time intervals
  • repeat experiments.