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CIE iGCSE Co-Ordinated Science B11 Gas exchange in humans Exam Style Questions Paper 1

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Question

Which gas in expired air has a greater percentage composition than in inspired air?

A. carbon dioxide
B. methane
C. nitrogen
D. oxygen

▶️ Answer/Explanation
During gas exchange, oxygen is taken up by the blood and carbon dioxide is released from the blood into the alveoli. Therefore, expired air contains more carbon dioxide and less oxygen than inspired air. Nitrogen is not exchanged, and methane is not a normal component of air.
✅ Answer: (A)

Question

Which row shows the effect of physical activity on breathing?

▶️ Answer/Explanation

During physical activity, muscles contract more vigorously and require more energy (ATP) for contraction. This leads to an increased rate of respiration, which requires more oxygen and produces more carbon dioxide as a waste product.

The increased concentration of carbon dioxide in the blood is detected by the brain (respiratory centre). This triggers an increase in both the rate of breathing (breaths per minute) and the depth of breathing (tidal volume, or the amount of air taken in with each breath). This combination ensures that more oxygen enters the lungs and more carbon dioxide is removed from the blood to meet the demands of the active muscles.

Therefore, physical activity causes breathing to become faster and deeper, which corresponds to row A.

✅ Answer: (A)

Question

Which row shows the percentages for inspired air and expired air?

▶️ Answer/Explanation
Inspired air contains approximately 21% oxygen and 0.04% carbon dioxide. In expired air, some oxygen is used for respiration, so its percentage decreases to about 17%, while carbon dioxide increases to about 4%. Row A correctly shows inspired air with 21% oxygen and 0.04% carbon dioxide, and expired air with 17% oxygen and 4% carbon dioxide.
✅ Answer: (A)

Question

The diagram shows the human gas exchange system.

Which label shows the diaphragm?

▶️ Answer/Explanation
The diaphragm is a dome-shaped sheet of muscle located at the base of the chest cavity, separating the thorax from the abdomen.
It plays a key role in breathing by contracting and flattening to increase the volume of the chest cavity.
In diagrams, it is shown as the lowermost structure of the breathing system.
✅ Answer: (C)

Question

A student runs 5 km.

Which statement describes the change in the student’s breathing 5 minutes after the run ends?

A. Depth decreases and rate decreases.
B. Depth decreases and rate increases.
C. Depth increases and rate decreases.
D. Depth increases and rate increases.

▶️ Answer/Explanation
During exercise, breathing depth and rate increase to supply more oxygen and remove carbon dioxide. Five minutes after the run ends, the body is recovering and oxygen demand decreases. Therefore, both the depth and rate of breathing decrease as the body returns to its resting state.
✅ Answer: (A)
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