Which of the following structures is not involve in respiration?

Step 1: Analyze the question We need the structure that does not take part in respiration (gaseous exchange or the movement of air or gases in the body).

Step 2: Explain the concept Respiration structures help bring oxygen into the body and remove carbon dioxide. Different animals use different organs:

• Humans and mammals: nostrils, mouth, trachea, bronchi, lungs
• Spiders and scorpions: book lungs
• Insects: spiracles and tracheae
• Fish: gills

Step 3: Check each option

• A. Lung books (book lungs): These are respiratory organs in arachnids such as spiders and scorpions. They are involved in respiration.
• B. Mouth: Air can enter through the mouth, so it is part of the respiratory pathway in humans and other vertebrates. It is also used for gaseous exchange in some animals, such as amphibians, through the buccal cavity. It is involved.
• C. Stomach: This is a digestive organ that stores food and begins protein digestion with acid and pepsin. It has no role in gaseous exchange. It is not involved in respiration.
• D. Trachea: This is the windpipe in vertebrates, and the tracheal tubes in insects. It carries air, so it is involved.

Step 4: Answer The stomach is a digestive structure, not a respiratory one, so the answer is C.

Tip: When a "which is NOT" question mixes organs from different systems, sort them into groups (digestive, respiratory, excretory) and pick the odd one out. Here, three options are for breathing and only the stomach is for digestion.