The experimental set-up given below demonstrates anaerobic respiration in germinating seeds. Read the information below the figure and answer the following questions :

Seeds can respire anaerobically for some time but later the radicles dry up and seedlings could not be produced. Soaked seeds are peeled and placed over mercury for germination.

(a) Why do we fill mercury in the test tube ? Can we do the same experiment in water or air ?

(b) Name the gas released by the germinating seeds, shown (A) in the figure.

(c) Can we do the above experiment with the seeds without peeling them ?

(d) How can we test the gas released in the above set-up ? Explain in short.

(e) How can we set the 'control set-up' for the above experiment ?

(a) Mercury is used because it excludes air and prevents oxygen from entering the test tube, thus creating anaerobic conditions. It also does not dissolve gases easily, so the gas released can collect at the top.
We cannot use air because it contains oxygen and would make respiration aerobic. Water is also not suitable because it contains dissolved gases and can dissolve carbon dioxide, preventing proper collection of the gas.

(b) The gas released by the germinating seeds is carbon dioxide.

(c) Yes, the experiment can be done without peeling the seeds, but peeling the seed coat hastens the outward diffusion of carbon dioxide.

(d) The gas released can be tested by introducing potassium hydroxide (KOH) into the test tube. KOH absorbs carbon dioxide, causing the mercury level to rise again. Alternatively, carbon dioxide can be confirmed by passing the gas through limewater, which turns milky due to the formation of calcium carbonate.

(e) A control set-up can be prepared in the same way, but with boiled and sterilised seeds instead of germinating seeds. Since boiled seeds are dead, they do not respire and no gas is produced.