The following processes are involved during expiration in man except

Analyze the question: We need the option that does NOT happen during expiration (breathing out).

Concept: Breathing out (expiration) is the reverse of breathing in (inspiration).

| Inspiration | Expiration | |---|---| | External intercostal muscles contract | External intercostal muscles relax | | Ribs move upwards and outwards | Ribs move downwards and inwards | | Sternum moves outwards and upwards | Sternum moves inwards and downwards | | Diaphragm contracts and flattens | Diaphragm relaxes and becomes dome-shaped | | Thoracic cavity volume increases | Thoracic cavity volume decreases | | Lung pressure falls, so air rushes in | Lung pressure rises, so air is forced out |

Step-by-step check of each option:

• A. The intercostal muscles relax: True. Relaxation of the intercostal muscles allows the ribcage to fall back. This is part of expiration.
• B. The thoracic cavity first increases in volume: False. During expiration the thoracic cavity decreases in volume. Volume increases during inspiration. This is the exception.
• C. The sternum moves inward: True. The sternum returns inward and downward as the chest shrinks.
• D. The ribs are moved downwards and inwards: True. This reduces the size of the chest cavity.

Answer: The question asks for the exception, which is B. The thoracic cavity decreases in volume during expiration, so this statement is wrong.

Exam tip: When you see "except" in a question, three options will be true and one false. For breathing, remember that expiration reverses everything in inspiration: muscles relax, ribs go down and in, the diaphragm domes up, volume goes down, and pressure goes up. Any option that says volume increases in expiration is the odd one out.