Which of these will be seen in our respiratory system ?
I. The absence of cartilage in small bronchioles allows them to expand .
II. The walls of the alveoli are made of cuboidal epithelium .
III. The recoil of the elastic fibres surrounding the alveoli helps to move air out during expiration.
IV. The trachea and bronchi are supported by circles of cartilage.

Options

A. I and II
B. I and III
C. II and IV
D. III and IV

Answer

To solve the question regarding which statements are true about the respiratory system, let's analyze each statement step by step.

### Step 1: Analyze Statement I
**Statement I:** The absence of cartilage in small bronchioles allows them to expand.

- **Explanation:** This statement is true. Small bronchioles do not have cartilage in their walls, which allows them to be more flexible and expand during the process of breathing.

### Step 2: Analyze Statement II
**Statement II:** The walls of the alveoli are made of cuboidal epithelium.

- **Explanation:** This statement is false. The walls of the alveoli are made up of simple squamous epithelium, which is thin and allows for efficient gas exchange. Cuboidal epithelium is not found in the alveoli.

### Step 3: Analyze Statement III
**Statement III:** The recoil of the elastic fibers surrounding the alveoli helps to move air out during expiration.

- **Explanation:** This statement is true. The elastic fibers in the lungs allow the alveoli to stretch during inhalation and recoil during exhalation, helping to push air out of the lungs.

### Step 4: Analyze Statement IV
**Statement IV:** The trachea and bronchi are supported by circles of cartilage.

- **Explanation:** This statement is partially true but misleading. The trachea is supported by C-shaped rings of hyaline cartilage, while the bronchi have irregular plates of cartilage rather than complete circles. Therefore, this statement is not entirely correct as it implies that both structures are supported by circles of cartilage.

### Conclusion
Based on the analysis:
- **True Statements:** I and III
- **False Statements:** II and IV

### Final Answer
The correct statements regarding the respiratory system are I and III.