The diagram shows the human breathing system.
Which labels show structures that produce changes in volume and pressure during ventilation of the lungs?
A) 1 and 3
B) 1 only
C) 2 and 3
D) 2 and 4
▶️ Answer/Explanation
Ans: A
During ventilation, the diaphragm (1) contracts and flattens, increasing thoracic volume, while the intercostal muscles (3) lift the ribs, further expanding the chest cavity. These actions reduce lung pressure, allowing air to flow in.
Structures labeled 2 (trachea) and 4 (alveoli) are involved in air passage and gas exchange but do not actively change volume or pressure. Thus, the correct answer is A (1 and 3).
These changes occur in the human body during exercise.
- breathing rate increases
- the rate of respiration increases
- nerve impulses sent from the brain to the intercostal muscles and diaphragm
- receptors in the brain detect increased concentration of carbon dioxide in the blood
What is the correct order for these changes?
A) 1 → 2 → 4 → 3
B) 1 → 3 → 4 → 2
C) 2 → 1 → 4 → 3
D) 2 → 4 → 3 → 1
▶️ Answer/Explanation
Ans: D
The correct sequence begins with increased respiration (2) due to higher energy demand during exercise. This produces more CO₂, which is detected by brain receptors (4). The brain then sends nerve impulses (3) to respiratory muscles, leading to an increased breathing rate (1) to remove excess CO₂. Thus, the logical order is 2 → 4 → 3 → 1 (Option D).