All of the following statements are correct, expect

Options

A. RCBs of human are not capable of metabolising glucose to carbon dioxide aerobically
B. No mixing of blood occurs in heart of a fish
C. With increase in heart rate, duration of a single cardiac cycle decreases
D. Pacemaker of human heart is a specialised neural tissue which maintains rhythmic activity of heart

Answer

To solve the question "All of the following statements are correct, except," we need to evaluate each statement provided in the options and identify which one is incorrect.

### Step-by-Step Solution:

1. **Evaluate the first statement**:
- "Red blood cells of humans are not capable of metabolizing glucose to carbon dioxide aerobically."
- **Analysis**: This statement is correct. Human red blood cells lack mitochondria, which means they cannot perform aerobic respiration to metabolize glucose into carbon dioxide. Instead, they primarily rely on anaerobic glycolysis.

2. **Evaluate the second statement**:
- "No mixing of blood occurs in the heart of a fish."
- **Analysis**: This statement is incorrect. Fish have a single circulatory system where deoxygenated blood and oxygenated blood can mix in the heart. Therefore, this statement does not hold true.

3. **Evaluate the third statement**:
- "Increase in the heart rate, duration of the single cardiac cycle decreases."
- **Analysis**: This statement is correct. When the heart rate increases, the duration of each cardiac cycle (which includes both systole and diastole) decreases.

4. **Evaluate the fourth statement**:
- "The pacemaker of the human heart, which is the SA node, is a specialized neural tissue that maintains rhythmic activity of the heart."
- **Analysis**: This statement is correct. The SA node is indeed a specialized group of cells that generates electrical impulses to regulate heart rhythm.

### Conclusion:
After evaluating all the statements, we find that the second statement is the incorrect one. Therefore, the answer to the question is the second statement.

### Final Answer:
The incorrect statement is: "No mixing of blood occurs in the heart of a fish."

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