In the experimental set-up to show that "the germinating seeds give out carbon dioxide", answer the following questions: (i) Why do we keep the conical flask airtight? (ii) Name the substance kept in the small test tube inside the conical flask. Write its role. (iii) Why does water rise in the delivery tube?
(i) We keep the conical flask airtight so that the carbon dioxide produced by the germinating seeds does not escape out. If this carbon dioxide escapes out of the conical flask, there will be no rise in the level of water in the glass tube.
(ii) The substance kept in the small tube is KOH (potassium hydroxide). Its role is to absorb the CO2 produced by the germinating cells which create a partial vacuum in the flask.
(iii) The rise in the water level in the tube indicates the production of CO2 by the germinating seeds. The KOH absorbs the CO2 produced by the germinating seeds and thus creates a partial vacuum in the flask. The air present in the glass bent tube moves into the conical flask, as a result of which the water is pulled further up in the bent tube.