Which of the following help the lungs to be such good organs for gaseous exchange?

Options

A. They are close to the heart.
B. They have a small surface area.
C. The air in the alveoli and blood in the capillaries are separated by a very thin layers of cells.
D. The haemoglobin carries lots of oxygen.

Answer

To determine which factors help the lungs to be effective organs for gaseous exchange, we can analyze each of the given options step by step.

### Step-by-Step Solution:

1. **Understanding Gaseous Exchange**: The primary function of the lungs is to facilitate the exchange of gases, specifically oxygen and carbon dioxide, between the air and the bloodstream.

2. **Evaluating Option 1 - Proximity to the Heart**:
- While the lungs are indeed close to the heart, this proximity does not directly enhance their ability to exchange gases. The heart's role is to pump blood, but it does not influence the efficiency of gas exchange in the lungs.

3. **Evaluating Option 2 - Small Surface Area**:
- A small surface area would actually hinder gaseous exchange. The larger the surface area, the more space there is for gas molecules to diffuse between the air in the alveoli and the blood in the capillaries. Therefore, this option is incorrect.

4. **Evaluating Option 3 - Thin Layers of Cells**:
- The air in the alveoli and the blood in the capillaries are separated by very thin layers of cells. This thin barrier allows for efficient diffusion of gases, making it a crucial factor in effective gaseous exchange. Thus, this option is correct.

5. **Evaluating Option 4 - Hemoglobin's Role**:
- Hemoglobin does carry oxygen in the blood, but the question specifically asks about the lungs' structural features that facilitate gas exchange. While hemoglobin's ability to carry oxygen is important, it does not directly relate to the lung's structural efficiency in gas exchange.

6. **Conclusion**:
- Based on the evaluation, the correct answer is **Option 3**: the air in the alveoli and blood in the capillaries are separated by very thin layers of cells, which is essential for efficient gaseous exchange.