Assertion : The role of oxygen in the regulation of respiratory rhythm is quite insignificant.
Reason : Increased `PCO_(2)` and `H^(+)` concentration inputs from chemoreceptors can activate respirotory rhytm centre to make necessary adjustments.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. If both assertion and reason are true and reason is not the correct explanation of assertion
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Answer

### Step-by-Step Solution

1. **Understanding the Assertion**: The assertion states that the role of oxygen in regulating the respiratory rhythm is quite insignificant. This implies that oxygen levels do not play a major role in controlling how we breathe.

2. **Understanding the Reason**: The reason provided states that increased partial pressure of carbon dioxide (PCO₂) and hydrogen ion concentration (H⁺) inputs from chemoreceptors can activate the respiratory rhythm center to make necessary adjustments. This suggests that the body primarily responds to changes in carbon dioxide and pH levels rather than oxygen levels.

3. **Role of the Respiratory Centers**: The respiratory rhythm is primarily controlled by centers located in the brain, particularly the pneumotaxic center in the pons region. This center moderates the function of the respiratory rhythm center and helps control the duration of inspiration.

4. **Chemoreceptors and Their Function**: Chemoreceptors located in the carotid and aortic bodies detect changes in the blood's carbon dioxide and hydrogen ion concentrations. When carbon dioxide levels rise, the pH of the blood decreases (becomes more acidic), which is sensed by these chemoreceptors.

5. **Impact on Respiratory Rate**: When the chemoreceptors detect increased PCO₂ and H⁺ concentrations, they send signals to the respiratory centers to adjust the breathing rate accordingly. This means that the respiratory rate is more significantly influenced by carbon dioxide levels than by oxygen levels.

6. **Conclusion**: Since the assertion claims that oxygen's role is insignificant and the reason correctly explains how carbon dioxide and hydrogen ions regulate breathing, both the assertion and reason are true. The reason is a correct explanation of the assertion.

### Final Answer
Both assertion and reason are true, and the reason is the correct explanation of the assertion.

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