A Planaria worm is cut horizontally in he middle into two halves P and Q such that the part P contains the whole head of the worm. Another Planaria worm is cut vertically into two halves R and S in such a way that both the cut pieces R and S contain half head each. Which of the cut pieces of the two Planaria worms could regenerate to from the complete respective worms ?

Options

A. only
B. only R and S
C. P,R and S
D. P,Q,R and S

Answer

To solve the question regarding the regeneration capabilities of the Planaria worms cut in different ways, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Cuts**:
- The first Planaria worm is cut horizontally into two parts: P (which contains the whole head) and Q (which contains the tail).
- The second Planaria worm is cut vertically into two parts: R and S (both parts contain half of the head).

2. **Regeneration Ability of Planaria**:
- Planaria is known for its remarkable ability to regenerate lost parts. This ability is due to the presence of specialized cells called neoblasts, which can differentiate into various cell types to replace lost tissues.

3. **Analyzing Part P**:
- Part P contains the entire head of the worm. Since it has the head, it has the necessary structures and cells to regenerate the rest of the body. Therefore, Part P can regenerate into a complete Planaria worm.

4. **Analyzing Part Q**:
- Part Q, which is the tail section, does not have the head. While Planaria can regenerate from tail sections, it is less efficient than from head sections. However, it can still regenerate to form a new worm, but it will not be complete without the head.

5. **Analyzing Parts R and S**:
- Both parts R and S contain half of the head. Planaria has the ability to regenerate from any part that contains part of the head. Therefore, both R and S can regenerate into complete Planaria worms.

6. **Conclusion**:
- The parts that can regenerate into complete Planaria worms are:
- Part P (from the horizontal cut)
- Part R (from the vertical cut)
- Part S (from the vertical cut)
- Part Q can regenerate but will not be a complete worm.

### Final Answer:
Parts P, R, and S can regenerate into complete Planaria worms, while Part Q can regenerate but will not be complete.

---