To show experimentally that carbon dioxide is given out during respiration (Method-II) - Lab Work

To show experimentally that carbon dioxide is given out during respiration - Science Practicals

Method -II : There are two methods to do this experiment. We are giving both of them. Students are advised to perform any one based on the availability of the materials in their lab.

To show experimentally that carbon dioxide is given out during respiration.

Respiration is a catabolic process wherein food is oxidized to release energy for various life processes. It is of two types:
(i) aerobic respiration that takes place in the presence of oxygen
(ii) anaerobic respiration that takes place in the absence of oxygen.
In aerobic respiration the breakdown of food (glucose) leads to the release of carbon dioxide gas, water and energy in the form of adenosine triphosphate (ATP). Most organisms that we see around us undergo aerobic respiration. Yeast and certain microorganisms and cells of skeletal muscles in our body undergo anaerobic respiration.
The overall reaction mechanism of aerobic respiration involves the oxidation of carbohydrate and the subsequent production of CO2, H2O and energy.
C6H12O6+6O2 → 6CO2 + 6H2O + Energy

Materials Required
Germinating gram seeds, phenol red indicator, petroleum jelly, a thistle funnel, a delivery tube, rubber tubing, boiling tube, a test tube, a two-bore rubber cork, a pinch cock and a stand with clamp,

Step 1: About twenty germinating seeds are placed in a boiling tube containing some water in it.
Step 2. A two-bore rubber cork is fitted to the mouth of the boiling tube. The set up is made by air-tight by applying a thin smear of petroleum jelly so that the gas evolved during the process of respiration by the germinating seeds does not leak out.
Step 3: A thistle funnel is fixed through one of the bores in the cork. The lower end of thistle funnel is dipped in water.
Step 4: A delivery tubeis passed  through the second bore of the cork and a rubber tubing is attached to the delivery tube. It is folded backwards and a pinch cock is fixed. Using a clamp, the boiling tube is fixed to a stand.
Step 5: The set-up is placed in bright sunlight for about one hour.
Step 6: About 1 mL of water is taken in a test tube (1 drop of water has a volume of nearly 0.1 mL). Two drops of phenol red indicator is added to it and shaked. Colour is noted.
Step 7: The free end of rubber tubing is dipped into the test tube containing phenol red indicator solution and the pinch cock is released.
Step 8: A few mL of water through the thistle funnel is poured into the boiling tube containing germinating gram seeds.
Step 9: Bubbles of a gas emerging from the rubber tube dipped in the phenol red indicator solution is observed. The test tube is shaken vigorously and the change in the colour of indicator is noted. Observations are recorded.

Colour of dilute phenol red indicator in the beginning of experiment isred. After keeping the boiling tube in bright sunlight for about an hour and on passing the evolved gas from the boiling tube through
the indicator, the colour of phenol red indicator changes to yellow/orange.

Results and Discussion

The pH indicator phenol red is used to estimate the amount of CO2 present. Therefor, the change in colour of phenol red solution from red to yellow/orange indicates that CO2 has been evolved in the tube and carbonic acid is formed with the reaction to water.

1.Take sufficient number of germinating seeds.
2. Keep the set up in bright sunlight.
3. Apparatus must be air-tight. Check all joints and apply petroleum jelly so that the evolved gas does not escape from the boiling tube.

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