Which of the following is correct for the common cockroach ?

Options

A. Malpighian tubules are excretory organs projecting out from the colon
B. Oxygen in transported by haemoglobin in blood
C. Nitrogenous excretory product is urea
D. The food is grinded by mandibles and gizzard

Answer

To determine the correct statement about the common cockroach, we will analyze each option provided in the question step by step.

### Step-by-Step Solution:

1. **Analyze Option 1**:
- The statement claims that Malpighian tubules are the excretory organs projecting out from the colon.
- **Evaluation**: Malpighian tubules are indeed the excretory organs in cockroaches, but they project out from the midgut, not the colon (which is part of the hindgut).
- **Conclusion**: This statement is incorrect.

2. **Analyze Option 2**:
- The statement claims that oxygen is transported by hemoglobin in the blood.
- **Evaluation**: In cockroaches, the respiratory pigment is not hemoglobin; it is haemocyanin. Hemoglobin is not present in their blood for oxygen transport.
- **Conclusion**: This statement is also incorrect.

3. **Analyze Option 3**:
- The statement claims that the nitrogenous excretory product is urea.
- **Evaluation**: Cockroaches excrete nitrogenous waste primarily in the form of ammonia, not urea.
- **Conclusion**: This statement is incorrect.

4. **Analyze Option 4**:
- The statement claims that food is ground by the mandibles and gizzard.
- **Evaluation**: This is true; in cockroaches, food is indeed grinded by the mandibles (jaws) and the gizzard (a muscular part of the digestive system).
- **Conclusion**: This statement is correct.

### Final Answer:
The correct statement about the common cockroach is: **The food is grinded by the mandible and gizzard.**