Rate of breathing is maximally affected by

Options

A. oxygen in trachea
B. concentration of `O_(2)`
C. concentration of `CO_(2)`
D. diaphragm expansion

Answer

To solve the question regarding what maximally affects the rate of breathing, we can follow these steps:

### Step 1: Understand the Factors Affecting Breathing Rate
Breathing rate can be influenced by various factors, including:
- Oxygen levels in the trachea
- Concentration of oxygen in the blood
- Concentration of carbon dioxide (CO2) in the blood
- Diaphragm expansion

### Step 2: Analyze Each Option
- **Option A: Oxygen in trachea** - While oxygen levels are important, they are not the primary factor affecting the rate of breathing.
- **Option B: Concentration of oxygen** - Oxygen concentration does play a role, but it is not the most significant factor.
- **Option C: Concentration of CO2** - High levels of CO2 in the blood are known to stimulate the respiratory center in the brain, leading to an increased rate of breathing. This is a critical factor.
- **Option D: Diaphragm expansion** - While diaphragm movement is essential for breathing, it is a mechanical process rather than a chemical one that affects the rate.

### Step 3: Determine the Most Influential Factor
Based on the analysis, the concentration of CO2 is the most significant factor that affects the rate of breathing. Increased CO2 levels lead to an increase in the rate of respiration to expel the excess CO2.

### Conclusion
The correct answer is **Option C: Concentration of CO2**.

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