Read the following statements about respiratory system of humans :
I. Type II alveoli help in secretion of a chemical surfactant called lecithin , which decreases the surface tension around alveoli.
II. The diffusion membrane for exchange of gases is made up of three major cellular layers.
III. Binding of oxygen with hemoglobin is primarily related to the partial pressure of `O_2`.
IV. Every 100 ml of oxygenated blood can deliver around 5 ml `CO_2` to the tissues under normal physiological conditions.
How many statement is /are correct from the above ?

Options

A. Two
B. Three
C. Four
D. One

Answer

To solve the question, we will analyze each statement regarding the respiratory system of humans and determine how many of them are correct.

### Step-by-Step Solution:

1. **Statement I**: "Type II alveoli help in secretion of a chemical surfactant called lecithin, which decreases the surface tension around alveoli."
- **Analysis**: This statement is correct. Type II alveolar cells (pneumocytes) secrete surfactant, which contains phospholipids like lecithin. This surfactant reduces surface tension in the alveoli, preventing their collapse and aiding in lung function.

2. **Statement II**: "The diffusion membrane for exchange of gases is made up of three major cellular layers."
- **Analysis**: This statement is also correct. The diffusion membrane consists of:
- The squamous epithelium of the alveoli.
- The endothelium of the capillaries.
- The basement membrane that lies between these two layers.
Therefore, there are indeed three layers involved in gas exchange.

3. **Statement III**: "Binding of oxygen with hemoglobin is primarily related to the partial pressure of O₂."
- **Analysis**: This statement is correct. The binding of oxygen to hemoglobin is indeed influenced primarily by the partial pressure of oxygen (pO₂). However, it is also affected by other factors like pCO₂, pH, and temperature, but the statement does not specify that these factors are primary, so it is still considered correct.

4. **Statement IV**: "Every 100 ml of oxygenated blood can deliver around 5 ml CO₂ to the tissues under normal physiological conditions."
- **Analysis**: This statement is incorrect. Under normal physiological conditions, every 100 ml of oxygenated blood can deliver approximately 15 ml of CO₂ to the tissues, not 5 ml. Therefore, this statement is false.

### Conclusion:
- **Correct Statements**: I, II, and III are correct.
- **Incorrect Statement**: IV is incorrect.

### Final Answer:
**Total Correct Statements**: 3