Presence of motile stage in life cycle & requirement of water as a medium to complete life cycle is diagnostic characters of

Options

A. Thallophyta
B. Bryophyta
C. Pteridophyta
D. Cryptogams

Answer

To solve the question regarding the presence of a motile stage in the life cycle and the requirement of water as a medium to complete the life cycle, we can follow these steps:

### Step-by-Step Solution

1. **Understanding the Question**: The question asks for a group of organisms that have a motile stage in their life cycle and require water to complete their life cycle.

2. **Identifying Groups in Plant Kingdom**:
- **Thalophyta**: This group includes algae, fungi, and lichens. These organisms are primarily non-motile, which means they do not have a motile stage in their life cycle. Therefore, this option can be eliminated.
- **Bryophyta**: This group includes mosses and liverworts. In bryophytes, the male gametes (sperm) are motile and swim through water to reach the female gametes (eggs). However, the female gametes are not motile. Thus, while there is a motile stage, it does not fully meet the requirement since the females are non-motile.
- **Pteridophyta**: This group includes ferns and horsetails. In pteridophytes, both male and female gametes are involved in the life cycle. The male gametes are motile and swim through water to fertilize the female gametes. This group also has a free-living sporophyte stage and exhibits an alternation of generations.

3. **Conclusion**: Based on the analysis, the group that meets both criteria (presence of a motile stage and requirement of water) is **Pteridophyta**.

### Final Answer
The presence of a motile stage in the life cycle and the requirement of water as a medium to complete the life cycle is a diagnostic character of **Pteridophyta**.

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