In mature RBC, nucleus is present in

Options

A. (a) Frog
B. (b) Rabbit
C. (c) Both (a) and (b)
D. (d) Neither in frog nor in rabbit

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the presence of a nucleus in mature red blood cells (RBCs) and which organism exhibits this characteristic.

2. **Identifying Organism Categories**: Recognize that organisms can be categorized into different classes, particularly vertebrates, which include mammals and non-mammals (like fish, amphibians, reptiles, and birds).

3. **Nucleus in RBCs**: In non-mammalian vertebrates (like fish, amphibians, reptiles, and birds), mature RBCs contain a nucleus. In contrast, mammals have evolved to have non-nucleated RBCs at maturity.

4. **Evolutionary Context**: Understand the evolutionary timeline:
- Fish (Pisces) → Amphibians → Reptiles → Birds → Mammals
- As evolution progressed, mammals adapted to have non-nucleated RBCs to maximize space for hemoglobin, enhancing oxygen transport.

5. **Analyzing Options**:
- Option A: Frog (Amphibian) - Frogs have nucleated RBCs.
- Option B: Rabbit (Mammal) - Rabbits have non-nucleated RBCs.
- Option C: Both A and B - Incorrect because only A is correct.
- Option D: Neither A nor B - Incorrect since A is correct.

6. **Conclusion**: The correct answer is option A, as mature RBCs in frogs (an amphibian) contain a nucleus.

**Final Answer**: In mature RBCs, the nucleus is present in frogs.

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