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CBSE Class 7 Science Question 10 of 10

Life Processes in Animals — Question 12

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12
Question
Rakshita designed an experiment taking two clean test tubes, A and B and filled them with lime water as shown in the figure. In test tube A, the surrounding air that we inhale was passed on by sucking air from the pipe, and in test tube B, the exhaled air was blown through the pipe (Fig. 9.16). What do you think she is trying to investigate? How can she confirm her findings? Fig. Experimental set-up
Answer

Rakshita is trying to inve stigate the gas we inhale and exhale while breathing. The lime water in test tube B turned milky (or cloudy), but the lime water in test tube A did not. Lime water turns milky when it reacts with carbon dioxide. Therefore, this indicates that the exhaled air contains more carbon dioxide than the air we inhaled.
Class 7 Life Processes in Animals Question Answer (Activities)
Activity 9.1: Let Us Investigate (Page 123)
Table 9.1: Action of saliva on starch
Test tube
Initial colour before adding iodine
Final colour after adding iodine
Possible reason for the change in colour
A: Boiled rice
White
Blue-black
Boiled rice contains starch, which reacts with iodine to give a blue-black colour.
B: Chewed boiled rice
White or slightly off-white
No change/ Faint blue black
Saliva contains a digestive juice that breaks down starch into sugars, reducing the starch content. Hence, little or no blue-black colour appears.
Activity 9.2: Let Us Make a Model (Page 130)
Fig. (a) Inhalation (b) Exhalation
Observation and conclusion:
• This experiment mimics the inhalation and exhalation processes of breathing. When the rubber sheet at the base of the bottle is pulled downward, the space inside the bottle increases. As a result, air is drawn into the balloon, and it inflates, just like the lungs do during inhalation. This shows how the diaphragm moves down and creates an area in the chest, allowing air to flow into the lungs.
• When the rubber sheet is pushed back upward, the space inside the bottle decreases and pressure increases, forcing air out of the balloon. This shows exhalation, where the diaphragm relaxes and moves up, reducing space and pushing air out of the lungs.
Activity 9.3: Let Us Explore (Page 131)
Fig. (a) Air is passed into lime water with a pichkari/syringe
(b) Air is exhaled into lime water
Observation: The lime water in test tube B turns milky as it receives exhaled air but the lime water in test tube A does not.
Conclusion: This indicates that exhaled air contains carbon dioxide. Lime water reacts with carbon dioxide to form calcium carbonate, which causes the milky appearance. The change only in test tube B confirms that more carbon dioxide is present in the air we breathe out than in the air we breathe in.