Chapter 9 Solutions — Life Processes in Animals

The correct option is (iii) To help in inhalation and exhalation.

The diaphragm is a dome-shaped muscle located below the lungs. During inhalation, the diaphragm moves downwards. This increases the space inside the chest, allowing air to enter the lungs. During exhalation, the diaphragm moves upwards, reducing space inside the chest and pushing air out of the lungs.

Why the other options are wrong:

Option (i) — Filtering air is done by the tiny hair and mucus in the nostrils and nasal passages, not the diaphragm.

Option (ii) — The diaphragm does not produce sound; it is a breathing muscle.

Option (iv) — Absorption of oxygen occurs at the alveoli in the lungs, not at the diaphragm.

Tanu's statement — 'We inhale air rich in oxygen' — is the most correct.

Explanation:

Anu says 'We inhale air.' This is partially correct because we do inhale air, but it does not specify the composition. Air is a mixture of gases including oxygen, nitrogen, carbon dioxide, and others.

Shanu says 'We inhale oxygen.' This is incorrect. We do not inhale pure oxygen; we inhale air, which contains approximately 21% oxygen along with nitrogen and other gases.

Tanu says 'We inhale air rich in oxygen.' This is the most accurate statement. The inhaled air contains nearly 21% oxygen, which is higher compared to the exhaled air (which contains only about 16–17% oxygen). So we inhale air that is relatively rich in oxygen.

Therefore, Tanu's statement correctly describes what we inhale — air (a mixture of gases) that is rich in oxygen.

The text tells us that the nostrils and nasal passages contain tiny hair and mucus that help trap dust and dirt from the air we breathe. When we inhale a lot of dust-laden air, the dust particles enter the nostrils and nasal passages.

Possible explanations for sneezing:

1. The dust particles irritate the lining of the nasal passages. Sneezing is a reflex action that forcefully expels air through the nose and mouth to clear the irritating dust particles from the nasal passages.

2. When a large amount of dust enters, the filtering mechanism (tiny hair and mucus) may become overwhelmed. Sneezing helps remove the excess dust that cannot be trapped by the hair and mucus alone.

3. Sneezing is a protective response — it helps prevent dust and other harmful particles from travelling further into the respiratory system (windpipe and lungs), thereby protecting the delicate tissues of the lungs.