Tracheids are found in all tracheophytes viz – Pteridophytes, gymnosperms and angiosperms.

Tracheids are specialized cells found in the xylem tissue of vascular plants. They play a crucial role in conducting water and providing mechanical support to the plant body. Among the given options, option B is the correct choice.

Explanation:
Importance of Tracheids:
Tracheids are responsible for the transportation of water and minerals from the roots to different parts of the plant. They form a continuous network of vessels that facilitate the movement of water through capillary action. Tracheids also provide structural support to the plant body, contributing to its overall strength.

Presence in Gymnosperms and Pteridophytes:
Tracheids are present in both gymnosperms and pteridophytes. Gymnosperms are a group of seed-bearing plants that include conifers, cycads, and ginkgo. Pteridophytes, on the other hand, are a group of seedless vascular plants that include ferns, horsetails, and clubmosses. Tracheids are one of the key features that distinguish vascular plants from non-vascular plants.

Characteristics of Tracheids:
Tracheids are elongated cells with tapered ends. They have thick, lignified secondary cell walls that provide strength and rigidity. The lignin present in their cell walls makes them impermeable to water, allowing them to withstand high pressures during water transport. The primary function of tracheids is to transport water, but they also play a role in providing mechanical support to the plant.

Differences from vessel elements:
Tracheids have certain distinct characteristics that differentiate them from vessel elements, another type of xylem cells found in angiosperms. Unlike vessel elements, tracheids are elongated cells with tapered ends and have pits in their cell walls. These pits allow lateral movement of water between adjacent cells. In contrast, vessel elements are shorter and wider, forming continuous tubes without tapered ends.

In conclusion, tracheids are specialized cells found in the xylem tissue of vascular plants. They are present in both gymnosperms and pteridophytes and provide mechanical support to the plant body. Tracheids have thick, lignified cell walls and play a crucial role in the transportation of water and minerals throughout the plant.