investigating respiration

• what is the first step of the practical?

  some lime soda granules are added to 2 test tubes. Soda lime absorbs the carbon dioxide produced by the respiring woodlice in the experiment.
• what is the second step of the practical?

  a ball of cotton wool is placed above the soda lime in each tube. Woodlice are placed on top of the cotton wool in 1 tube. Glass beads with the same mass as the woodlice are used in the control tube.
• what is the third step of the practical?

  the respirometer is then set up: the test tube contains soda lime, woodlice, and cotton wool. There is a syringe going into the lid of the control tube. The control tube has the same, but glass beads instead of woodlice. There is a manometer containing coloured fluid joining both the tubes. Both are in a water bath.
• what is the fourth step of the practical?

  the syringe is used to set the fluid in the manometer to a known level.
• what is the fifth step of the practical?

  the apparatus is then left for a set period of time in a water bath set to 15 degrees celcius.
• what is the sixth step of the practical?

  during this time, there'll be a decrease in the volume of the air in the test tube containing the woodlice. This is because the woodlice use up oxygen in the tube as they respire (the CO2 they produce is absorbed by the soda lime).
• what is the seventh step of the practical?

  the decrease in volume reduces the pressure in the tube, causing the coloured liquid in the manometer to move towards the test tube containing the woodlice.
• what is the eighth step of the practical?

  the distance moved by the liquid in a given time is measured. This value can then be used to calculate the volume of oxygen taken in by the woodlice per minute. This gives you the rate of respiration.
• what is the nineth step of the practical?

  repeat steps 1-8 with the water bath set at different temperatures, for example 20 and 25 degrees celcius, allowing you to see how changing the temperature affects the rate of respiration.
• what can you use instead of woodlice?

  germinating peas or beans
• what equipment do you need for the practical?

  • woodlice
  • a water bath
  • respirometer
  • soda lime
  • cotton balls
• how should the animals in this experiment be treated ethically?

  don't leave the woodlice in the respirometer for too long, or they may run out of oxygen and die.