Respiration in plants can be investigated by transport out experiments to show the production of carbon dioxide (CO2) and heat and consumption of oxygen. Some amount of energy is generated from the oxidation of food materials is released as heat. This can be proved by germinating seeds.
Requirements: One Thermo flask, some germinating Gram seeds, and a thermometer.
Procedure: Some germinating gram seeds are taken in the Thermo flask and closed its mouth tightly with a cork. A thermometer is introduced through the cork so that its bulb rests among the gram seeds. Note the mercury reading of the thermometer.
Fig: Experiment to Heat is Evolved during Respiration
Experiment to show Oxygen is used during respiration
Put some germinating seeds in a conical flask. With the help of a thread suspend a small tube containing KOH in the flask. Through the hole of the cork, pass a glass tube bent twice at right angles. One end of the tube is in the flask while the other end is in the beaker filled with water. Make the apparatus airtight. Note the level of water in the tube. Keep the apparatus for some time and note the position of water.
It is observed that water rises in the tube. The rise in the level of water is due to a partial vacuum created in the flask because the gas produced during respiration is absorbed by KOH.
This shows that germinating seeds produce CO2 during aerobic respiration as KOH can absorb CO2. This is aerobic respiration as KOH can absorb CO2 produced by seeds using air available.
The germinating seeds undergo aerobic respiration as they use the oxygen accessible within the conical flask. As entire of the oxygen is used up by the germinating seeds, the pressure in the flask is decreased. Hence, accordingly, the mercury level rises in the far end of the bent glass tube.
- Experiment to prove carbon dioxide is released during germination
Gas produced in flask A turns lime water milky showing carbon dioxide has been produced. Flask B does not turn lime water milky, showing the absence of carbon dioxide, because of boiled seeds.
- Experiment to show heat is evolved during respiration
The live seeds show an increase in the temperature; boiled seeds do not show any increase. Living seeds respire and evolve heat while the boiled seeds do not respire and do not evolve heat.
Observation: After some time an increase in the reading of mercury in the thermometer will be observed. The temperature in the flask with germinating seeds is higher than the temperature of the flask with dry deeds.
Conclusion: Rise of mercury indicates the rise of temperature. And this temperature is produced by the respiration of the germinating seeds. In dry seeds, enzymes are dormant so respiration did not take place and no increase in temperature whereas in germinating seeds enzymes are active and respiration has taken place with the increase in temperature.