Which one of the following is not true of organisms included in the kingdom Monera ?
(a) They reproduce by mitosis
(b) They originated at least 3.5 billion years ago
(c) They have prokaryotic cellular organisation
(d) Most have cell wall

Options

A. They reproduce by mitosis
B. They originated at least 3.5 billion years ago
C. They have prokaryotic cellular organisation
D. Most have cell wall

Explanation

To solve the question, we need to analyze each option provided regarding organisms in the kingdom Monera:

1. **Understanding Kingdom Monera**:
- Kingdom Monera includes prokaryotic organisms, primarily bacteria. These organisms are characterized by their simple cellular structure, lacking a well-defined nucleus and membrane-bound organelles.

2. **Evaluating Each Option**:
- **(a) They reproduce by mitosis**: This statement is **not true**. Organisms in Monera reproduce primarily through binary fission, not mitosis. Mitosis is a process of cell division that occurs in eukaryotic cells.
- **(b) They originated at least 3.5 billion years ago**: This statement is **true**. Monerans are among the earliest forms of life on Earth, dating back to at least 3.5 billion years.
- **(c) They have prokaryotic cellular organization**: This statement is **true**. Organisms in Monera are indeed prokaryotic, meaning they do not have a true nucleus or membrane-bound organelles.
- **(d) Most have cell walls**: This statement is **true**. Most bacteria, which are included in Monera, have a rigid cell wall.

3. **Conclusion**:
- The only statement that is not true for organisms in the kingdom Monera is option (a) "They reproduce by mitosis." Therefore, the correct answer is **(a)**.

### Summary of Steps:
1. Identify the characteristics of organisms in Kingdom Monera.
2. Analyze each option to determine its truthfulness.
3. Conclude which statement is not true.