Reproduction is characteristic of living organisms . Which of these orgenisms do not reproduce by fragmentation ?

Options

A. Unicellular algae
B. filamentous algae
C. portonema of mosses
D. flatworms

Answer

To solve the question "Which of these organisms do not reproduce by fragmentation?", we will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding Fragmentation**:
- Fragmentation is a form of asexual reproduction where an organism breaks into fragments, and each fragment can develop into a new organism. This method is common in certain multicellular organisms.

2. **Evaluating the Options**:
- **Option 1: Unicellular Algae**:
- Unicellular algae, such as diatoms, primarily reproduce through binary fission, not fragmentation. In binary fission, a single cell divides into two identical cells. Therefore, unicellular algae do not reproduce by fragmentation.

- **Option 2: Filamentous Algae**:
- Filamentous algae, like Spirogyra, reproduce by fragmentation. They can break into pieces, and each piece can grow into a new filamentous algae. Thus, this option does reproduce by fragmentation.

- **Option 3: Protonema of Moss**:
- Protonema is a stage in the life cycle of mosses (bryophytes) that can also reproduce by fragmentation. The filamentous structures can break apart and grow into new moss plants. Therefore, this option does reproduce by fragmentation.

- **Option 4: Flatworm**:
- Flatworms are known to reproduce by fragmentation as well. They can regenerate and form new individuals from fragments of their bodies. Thus, this option also reproduces by fragmentation.

3. **Conclusion**:
- After analyzing all the options, we find that the only organism that does not reproduce by fragmentation is **Option 1: Unicellular Algae**.

### Final Answer:
**Unicellular Algae** do not reproduce by fragmentation.