Which one of the following statements is incorrect

Options

A. The residual air in lungs slightly decreases the efficiency of respiration in mammals
B. The presence of non-respiratory air sacs, increases the efficiency of respiration in birds
C. In insects, circulation body fluids serve to distribute oxygen to tissues
D. The principle of counter current flow facilitates efficient respiration in gills of fishes

Answer

To determine which statement is incorrect, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Residual Air in Lungs**:
- The first statement claims that residual air in lungs slightly decreases the efficiency of respiration in mammals.
- Residual volume is the air that remains in the lungs after a person has exhaled completely. This air cannot be expelled and helps to keep the lungs inflated, which is essential for continuous gas exchange.
- Therefore, this statement is **correct** because residual air does not decrease efficiency; rather, it plays a crucial role in maintaining lung function.

2. **Analyzing Non-Respiratory Air Sacs in Birds**:
- The second statement suggests that the presence of non-respiratory air sacs increases the efficiency of respiration in birds.
- Birds have a unique respiratory system that includes air sacs, which allow for a continuous flow of air through the lungs, enhancing gas exchange efficiency.
- This statement is also **correct**.

3. **Examining Circulation in Insects**:
- The third statement states that in insects, circulation serves to distribute oxygen to tissues.
- Insects have a tracheal system that directly delivers oxygen to tissues, and while circulation does play a role, it is not the primary means of oxygen transport.
- This statement is somewhat misleading but can be considered **correct** in the context of the question.

4. **Counter Current Flow in Fish Gills**:
- The fourth statement mentions that the principle of counter current flow facilitates efficient respiration in the gills of fishes.
- The counter current exchange mechanism allows for a more efficient transfer of oxygen from water to blood in fish gills, maximizing oxygen uptake.
- This statement is **correct**.

### Conclusion:
After analyzing all the statements, the first statement regarding residual air in lungs is the only one that could be considered misleading. However, it is technically correct in the context of how it is phrased.

Thus, the answer to the question is that none of the statements provided are incorrect based on the context given. However, if we strictly follow the question's requirement to identify an incorrect statement, the first statement could be seen as the least accurate.

### Final Answer:
The first statement about residual air in lungs is the least accurate in terms of its phrasing, but all statements are fundamentally correct.

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