Life Processes in Animals — NCERT Solutions

Correct Statement: Tanu — "We inhale air rich in oxygen."

Reason:

• Anu's statement — "We inhale air" — is partially correct but incomplete. We do inhale air, but this statement does not specify the composition of inhaled air.

• Shanu's statement — "We inhale oxygen" — is incorrect. We do not inhale pure oxygen. The air we breathe is a mixture of gases including nitrogen (~78%), oxygen (~21%), carbon dioxide (~0.04%), and other gases.

• Tanu's statement — "We inhale air rich in oxygen" — is the most accurate. The air we inhale is a mixture of gases, and it is rich in oxygen (about 21%) compared to the exhaled air, which has a higher proportion of carbon dioxide and less oxygen.

Conclusion: Tanu's statement is correct because inhaled air is not pure oxygen but a mixture of gases that is rich in oxygen.

Given: Sneezing occurs when we inhale dust-laden air.

Possible Explanations:

1. Irritation of the nasal lining: When dust particles enter the nasal passages, they irritate the sensitive lining (mucous membrane) of the nose. The body responds by sneezing to forcefully expel the irritants.

2. Defence mechanism of the body: Sneezing is a reflex action — a protective mechanism of the body. When foreign particles like dust, pollen, or dirt enter the nasal passage, the body tries to remove them by a sudden, forceful expulsion of air through the nose and mouth (sneezing).

3. Overloading of the filtering system: The tiny hairs (cilia) and mucus in the nasal passages normally trap dust and dirt. When the amount of dust is too large for the hairs and mucus to handle, the body triggers a sneeze to clear the nasal passage.

Conclusion: Sneezing is a natural reflex action that helps protect the respiratory system by expelling dust, dirt, and other foreign particles from the nasal passages before they can reach the lungs.

Given: Both Paridhi and Anusha ran for their morning workout. After running, Anusha was breathing faster than Paridhi.

Possible Explanations:

1. Anusha ran faster or for a longer distance: If Anusha ran at a higher speed or covered a greater distance than Paridhi, her muscles would have worked harder and used more oxygen. To meet the increased demand for oxygen and to expel the extra carbon dioxide produced, her body would require faster breathing.

2. Anusha has lower physical fitness/stamina: If Anusha is less physically fit than Paridhi, her body is less efficient at using oxygen. Her heart and lungs have to work harder to supply the same amount of oxygen, resulting in faster breathing after exercise.

3. Anusha may have a smaller lung capacity: If Anusha's lungs can hold less air per breath compared to Paridhi's, she would need to breathe more frequently to take in the same amount of oxygen.

4. Anusha may have a health condition: Anusha might have a respiratory condition (such as mild asthma) that makes her breathing less efficient, causing her to breathe faster after physical exertion.

Conclusion: The rate of breathing after exercise depends on factors such as the intensity of exercise, physical fitness, lung capacity, and overall health of the individual.

Given:

• Test tube A: Rice flour + water (no saliva)
• Test tube B: Rice flour + water + saliva
• Both left for 35–45 minutes, then iodine solution added.
• From Fig. 9.15: Test tube A turns blue-black; Test tube B does not turn blue-black (remains orange-brown).

What Yadu wants to test:
Yadu wants to test whether saliva can break down starch (present in rice flour) into simpler substances (sugar). In other words, he is investigating the action of saliva on starch — specifically, whether the enzyme present in saliva (salivary amylase) digests starch.

Explanation of Results:

• Test tube A (no saliva): Starch is still present → iodine turns blue-black.
• Test tube B (with saliva): Saliva breaks down starch into sugar → no starch remains → iodine does NOT turn blue-black (stays orange-brown).

Conclusion: Yadu's experiment demonstrates that saliva contains a digestive enzyme that breaks down starch into sugar. This confirms that saliva plays an important role in the chemical digestion of starchy foods in the mouth.

Given:

• Test tube A: Lime water + inhaled (atmospheric) air passed through it.
• Test tube B: Lime water + exhaled air blown through it.

What Rakshita is trying to investigate:
Rakshita is trying to investigate whether exhaled air contains more carbon dioxide ($CO_2$) than the air we inhale (atmospheric air). She wants to compare the composition of inhaled air and exhaled air, specifically with respect to carbon dioxide content.

Expected Observations:

• Test tube A: Lime water remains clear (no change), because atmospheric air contains very little $CO_2$ (about 0.04%).
• Test tube B: Lime water turns milky (cloudy), because exhaled air contains a higher concentration of $CO_2$ produced during respiration.

Chemical Reaction:
$$Ca(OH)_2 + CO_2 \rightarrow CaCO_3 \downarrow + H_2O$$
Calcium hydroxide (lime water) reacts with carbon dioxide to form calcium carbonate (white precipitate), which makes the lime water appear milky.

How she can confirm her findings:

1. She can repeat the experiment multiple times to ensure consistent results.
2. She can use a $CO_2$ indicator or a gas analyser to measure the actual amount of $CO_2$ in inhaled and exhaled air.
3. She can show that the milky colour in test tube B is due to $CaCO_3$ by filtering the precipitate and testing it.

Conclusion: Rakshita's experiment confirms that exhaled air is richer in carbon dioxide than inhaled air, which is a product of the process of respiration occurring in the body's cells.