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CIE iGCSE Co-Ordinated Science B12. Respiration Exam Style Questions Paper 1

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Question

What are the products of aerobic respiration?

A. carbon dioxide and water
B. carbon dioxide and glucose
C. oxygen and glucose
D. oxygen and water

▶️ Answer/Explanation

Aerobic respiration is the chemical reactions in cells that use oxygen to break down nutrient molecules to release energy. The word equation for aerobic respiration is:

glucose + oxygen \(\rightarrow\) carbon dioxide + water

Therefore, the products of aerobic respiration are carbon dioxide and water. Glucose and oxygen are the reactants (substances that are used up in the reaction).

Option B incorrectly lists glucose as a product, Option C incorrectly lists oxygen and glucose as products, and Option D incorrectly lists oxygen as a product.

✅ 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

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)

Question

The list shows some processes that occur in the body.

  1. cell division
  2. oxygen diffusion
  3. protein synthesis
  4. temperature regulation

Which processes use energy released by respiration?

A. 1, 3 and 4
B. 1 and 2
C. 2, 3 and 4
D. 3 and 4 only

▶️ Answer/Explanation
Cell division (1), protein synthesis (3), and temperature regulation (4) all require ATP energy from respiration — cell division needs energy to replicate DNA and separate chromosomes, protein synthesis uses ribosomes requiring energy, and maintaining body temperature requires metabolic heat production.
Oxygen diffusion (2) is a passive process driven solely by the concentration gradient and requires no energy input from respiration.
✅ Answer: (A)

Question

Which row shows the changes that occur during exercise?

▶️ Answer/Explanation
During exercise, muscles respire faster and need more oxygen delivered and more carbon dioxide removed.
This means breathing rate increases and heart rate increases at the same time.
The correct row is the one in which both breathing rate and heart rate increase together.
✅ Answer: (A)
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