Theory of the experimentLike any other organism, all parts of higher plant organisms respire aerobically. In this aerobic respiration, the glucose molecules present in the cells of all plant parts get oxidized by consuming oxygen from the atmosphere. Through this oxidization chemical step, the reserved glucose molecules of plant cells are broken down to release six carbon dioxide molecules, six water molecules, 38 ATP molecules energy and little heat energy. This chemical reaction can be represented in the form of chemical formula as follow:-
C6H12O6 + 6 O2 ---------------> 6 CO2 + 6 H2O + 38 ATP + heat energy
But certain cells of plant parts under abnormal conditions respire anaerobically temporarily for certain time for their survival. In anaerobic respiration, the cells of plant parts in the absence of oxygen where glucose molecules are partially broken down to release two ethyl alcohol or ethanol molecules, two carbon dioxide molecules, two ATP molecules, and little heat energy. This chemical reaction can be represented in the form of chemical formula as follow:-
C6H12O6 (absence of oxygen)--------------> 2 C2H5OH + 2 CO2 + 2 ATP + Heat energy
So in anaerobic respiration only little energy is derived as glucose molecules are incompletely oxidized because of lack of oxygen.
Aim of the experimentTo demonstrate germinating seeds can undergo anaerobic respiration i.e. they can respire even in the absence of oxygen and evolve carbon dioxide.
Requirements for the experimentTwo beakers, peeled off germinating seeds, boiled dead germinating seeds, mercury liquid, and test tubes.
Carbon dioxide is evolved during anaerobic respiration of germinating seeds (Courtesy:- ICSE Board's question paper)
Procedure for the experimentTake 8-10 healthy bean seeds or pea seeds and soak them in water for one day before using them in the experiment. Take two beakers and fill 3/4 of them with mercury liquid. Take two test tubes and fill them with mercury. Then make them stand in an inverted position in the mercury of beakers. Take few germinating bean seeds and peel off their seed coats. These seeds should be carefully introduced into the inverted test tube of the first setup by using forceps. In the second setup, boiled germinating seeds (dead) bean seeds are introduced into the inverted test tube containing mercury. As mercury is heavy in density than seeds, the seeds rise to the top of the test tubes in both cases. As the seeds were completely immersed in mercury liquid, the seeds are subjected to anaerobic conditions. The second setup acts as a control setup. The control setup is an experimental setup where one of the conditions for the experiment is missing. In the second setup, the dead boiled seeds were taken and they were not expected to respire. The two setups were left undisturbed for about two days.
Observation and result After two days we can observe there is some gas collected at the top of the test-tube of the first setup while the test tube of the control setup remains the same. To find out the gas collected in the test-tube of the first setup, a pellet of Potassium hydroxide (KOH) introduced with the help of forceps. Immediately mercury rises to the top as the gas collected in the test-tube is absorbed by the KOH pellet. KOH is an excellent absorber of carbon dioxide gas. This observation clearly proves that the germinating seeds in the absence of oxygen evolve carbon dioxide.
In the second setup, there is no evolution of carbon dioxide as the seeds used in the experiment are dead. Dead seeds cannot germinate and so they cannot evolve carbon dioxide. Hence there is no accumulation of gas at the top of the test-tube of the second setup.
So the conclusion for the above experiment is germinating seeds only can respire anaerobically and evolve carbon dioxide while dry seeds cannot evolve carbon dioxide as they are inactive.
Precautions to be taken for the above experiment
Here is another experiment on Respiration in Plants
This is a good experiment and can be attempted by the students to showcase the anaerobic respiration. Anaerobic respiration is the first reaction of seeds to the surroundings and underneath the soil, they exhibit similar characteristics and produce the basic environment in which a new plant can emerge. The plant will grow as per the heredity code in the seed and later become a great environment protector.