|Experiment 2. The gas produced in respiration | | | |[pic] | |(a) Label two boiling tubes A and B and place a known weight or number of living organisms in A. | | |Place an equal quantity of dead or non-living material in B. | | |Cover the mouth of each tube with a piece of aluminium foil.
Press firmly into place round the rim| | |of the tube. | | |Leave the tubes for at least ten minutes.|(b) Use a graduated pipette or syringe to place 2 cm3 lime water in each of two clean test-tubes | | |and label these A and B. | | | | | |(c) You are provided with a syringe attached to a glass delivery tube drawn out to a fine point. | | |Check that the syringe plunger is pushed fully down in the barrel. | | | | | |(d) After the experiment has been running for ten minutes or more, push the delivery tube, still | | |attached to the syringe, through the foil cap of tube B.
Keeping the point of the delivery tube | | |close to the side of the boiling tube to avoid damaging the organisms, insert the delivery tube | | |into the midst of the organisms (see Figure 1). Withdraw the syringe plunger to fill the syringe | | |with air from the boiling tube. | | | | | |(e) Place the syringe and delivery tube in test-tube B containing lime water so that the delivery | | |tube is below the level of the liquid and gradually depress the plunger so that the air from the | | |syringe bubbles slowly through the lime water (see Figure 2 p.2. 02).
When all the air has been | | |expelled from the syringe, remove the delivery tube, close the mouth of the test-tube with your | | |thumb (or a cork) and shake the tube thoroughly for a few seconds. | | | | | |(f) Repeat the operation from (d) for boiling tube A, using test-tube A of clear lime water. | | | | | |(g) Compare the appearance of lime water in the two tubes. | |