What is the difference between-

i.Tracheids and vessels

ii.Sieve plates and sieve tubes

(i) Differences between tracheids and vessels

They are unicellular elements of xylem and are small in size.Vessels are multicellular and large in size.
They are narrow in lumen due to more lignified walls.They are broad in lumen due to less lignified walls.
The ends are tapering or oblique and closed.The ends are rounded and open.
They are found in pteridophytes, gymnosperms and a few angiosperms. They are found only in angiosperms.


For the second (ii) part of your question you may refer to the answer provided by your friends.

@Others...Good work..Keep posting!

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  • Tracheids:
  • Long, tubular dead cells with lignified walls and tapering ends
  • Possess various types of thickening for mechanical strength
  • Unthickened areas help in movement of water from one tracheid to another
  • Vessels:
    • Long tubules
    • Walls are lignified
    • Occur in flowering plants
    • More efficient than tracheids
    • Formed by end to end union of large number of dead cells
    • Vessels and tracheids are conducting elements of xylem. They conduct water and minerals vertically
  • Sieve Tubes:
    • Elongated, living, tubular conducting channels
    • Transverse end walls between adjacent sieve tubes cells are perforated – sieve plates
    • Have vacuolated cytoplasm
    • Nucleus degenerates
    • Cytoplasmic strands are continuous between adjacent sieve tubes
    • sieve cells:
      • Thin walled, small and elongated
      • Has dense cytoplasm and nucleus
      • Nucleus controls the sieve tubes and keeps them living
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Xylem vessels: Xylem vessels comprise a vertical chain of lengthened, dead cells known as vessel elements. The cells are arranged end to end and the cross-walls dissolve completely or have simple or complex perforation plates between successive cells. The secondary walls of vessels are impregnated with lignin and are thickened unevenly. The walls of the vessels may be thickened in different ways, e.g. annular, spiral and pitted thickening may be observed.

Xylem tracheids: A tracheids is an elongated cell, the contents of which are non-living. The cell walls are thickened, impregnated with lignin and the lumen is smaller. As in the case of vessels, there is a differentiation between annular, spiral and pitted tracheids again caused by the type of thickening of the secondary walls. Tracheids have no perforation plates.

Sieve Cells

1. Found in gymnosperms and pteridophytes.

2. Not associated with companion cells.

3. Sieve areas without sieve plates.

4. Long, elongated cells with tapering end walls.

Sieve Tubes

1. Found in angiosperms.

2. Associated with companion cells.

3. Sieve areas with sieve plates.

4. Shorter but wider cells placed one above the other and connected at the end walls by sieve pores.

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