Which of the following is correct for the common cockroach ?

Options

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

Explanation

To determine which statement is correct regarding the common cockroach, let's analyze each option step by step.

### Step 1: Analyze the first statement
**Statement 1:** Malpighian tubules are excretory organs projecting out from the colon.

- **Explanation:** The Malpighian tubules are indeed excretory organs in cockroaches, but they do not project out from the colon. Instead, they are located in the hemocoel and are responsible for excreting waste products, primarily uric acid. Therefore, this statement is **incorrect**.

### Step 2: Analyze the second statement
**Statement 2:** Oxygen is transported by hemoglobin in blood.

- **Explanation:** Cockroaches have an open circulatory system, meaning their blood (hemolymph) is not contained within blood vessels like in vertebrates. Instead, oxygen is transported directly in the hemolymph and not by hemoglobin as in vertebrates. Therefore, this statement is also **incorrect**.

### Step 3: Analyze the third statement
**Statement 3:** Nitrogenous excretory product is urea.

- **Explanation:** Cockroaches are uricotelic, which means they excrete nitrogenous waste primarily in the form of uric acid, not urea. Therefore, this statement is **incorrect**.

### Step 4: Analyze the fourth statement
**Statement 4:** The food is grinded by mandibles and gizzard.

- **Explanation:** In cockroaches, the mandibles are part of the mouthparts that help in grinding food, and the gizzard is a muscular structure that further grinds the food. This statement accurately describes the process of digestion in cockroaches. Therefore, this statement is **correct**.

### Conclusion
The correct statement regarding the common cockroach is **Statement 4: The food is grinded by mandibles and gizzard**.

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