Bryophytes don't attain much height because

Options

A. they do not have vascular supply
B. they do not have roots and mechanical tissue
C. they require water for transport of sperms
D. all of the above.

Answer

### Step-by-Step Solution:

1. **Understanding Bryophytes**: Bryophytes are non-vascular plants that include mosses, liverworts, and hornworts. They are characterized by their simple structure, lacking complex tissues.

2. **Absence of Vascular Tissue**: One of the primary reasons bryophytes do not attain much height is that they lack vascular tissue (xylem and phloem). Vascular tissue is essential for the transport of water and nutrients throughout the plant. Without it, bryophytes cannot effectively transport water from the soil to their upper parts, limiting their height.

3. **Lack of Roots**: Bryophytes do not have true roots. Instead, they have structures called rhizoids that anchor them to the substrate but do not absorb water and nutrients in the same way roots do. This further restricts their ability to grow tall.

4. **Need for Water for Reproduction**: Bryophytes require water for the transport of sperm to the egg during reproduction. The sperm in bryophytes is flagellated and needs a film of water to swim to the non-motile egg for fertilization. This dependence on water for reproduction also limits their habitat and growth.

5. **Conclusion**: Given these factors, bryophytes do not attain much height because they lack vascular supply, do not have true roots and mechanical tissues, and require water for the transport of sperm during reproduction. Therefore, the correct answer is "all of the above."