Which one of the following statements in incorrect ?

Options

A. The residual air in lungs slightly decrease the efficiency of respiration in mammals
B. The presence of non - respiratory air sacs increase the efficiency of respiration in birds
C. In insects , cirulating body fluids serve to distribute oxygen to tissue .
D. The principle of counter - current flow facilitates cells is transported to the lungs.

Explanation

To determine which statement is incorrect, we will analyze each option one by one.

### Step-by-Step Solution:

1. **Analyze Option 1**:
- Statement: "The residual air in lungs slightly decreases the efficiency of respiration in mammals."
- Explanation: Residual air (the air that remains in the lungs after a forceful exhalation) does indeed reduce the efficiency of respiration because it prevents complete exchange of gases. However, this statement is phrased in a way that suggests it is a negative impact, which is true. Therefore, this statement is **correct**.

2. **Analyze Option 2**:
- Statement: "The presence of non-respiratory air sacs increases the efficiency of respiration in birds."
- Explanation: Birds have air sacs that help in the continuous flow of air through their lungs, allowing for more efficient gas exchange. This statement is also **correct**.

3. **Analyze Option 3**:
- Statement: "Insects circulating body fluid serves to distribute oxygen to tissues."
- Explanation: Insects have a unique respiratory system where oxygen is delivered directly to tissues through a network of tracheae. They do not rely on hemolymph (their body fluid) to transport oxygen because hemolymph lacks oxygen-carrying pigments. Therefore, this statement is **incorrect**.

4. **Analyze Option 4**:
- Statement: "The principle of counter current flow facilitates cells' transport to the lungs."
- Explanation: The counter current flow principle is related to the exchange of gases in fish gills, where water flows in the opposite direction to blood flow, maximizing oxygen uptake. This statement is misleading as it suggests that it facilitates the transport of cells to the lungs, which is not accurate. Hence, this statement is also **incorrect**.

### Conclusion:
Both Option 3 and Option 4 contain inaccuracies, but since the question asks for one incorrect statement, we can conclude that **Option 3** is the primary incorrect statement regarding insect respiration.